Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2018SW002047

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DOI： 10.1051/e3sconf/20186201007

Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1051/e3sconf/20186201012

Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1051/e3sconf/20172001013

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/2017JA024246

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/2016RS006035

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2012JA017953

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2012JA017841

Language：English   Publishing type：Research paper (scientific journal)  

In order to correctly describe the dynamical behavior of the magnetosphere-ionosphere (MI) coupling system and the scale-dependent auroral process, we develop a synthesis formulation that combines the process of (1) the inverse Walen separation of MHD disturbance into parallel- and antiparallel-propagating shear Alfvén wave to the ambient magnetic field, (2) the shear Alfvén wave reflection process including (3) the scale-dependent electrostatic coupling process through the linearized Knight relation, (4) two-layer ionosphere model, and (5) dynamic conductance variations. A novel procedure that applies the inverse Walen relation to the incompressional MHD disturbances at the inner boundary of the MHD region enables to extract the component of the shear Alfvén wave incident to the ionosphere. The extracted incident electric field supplies an electromotive force for the generation of the MI coupling system, and the reflected electric field is generated such that it totally satisfies the synthesis MI-coupling equation. A three-dimensional ionospheric current system is represented by a two-layer model in which the Pedersen and the Hall current are confined in the separated layers, which are connected by field-aligned currents driven by the linear current-voltage relation between two layers. Hence, our scheme possibly reproduces two types of the scale-dependent MI-decoupling process of the perpendicular potential structure: due to the parallel potential drop at the auroral acceleration region and the other due to the parallel potential differences inside the ionosphere. Our newly formulation may be well suited for description of scale-dependent auroral process and mesoscale ionospheric electrodynamics interlocked with the dynamical development of magnetospheric processes.

DOI： 10.1029/2011JA016460

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2011JA016449

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DOI： 10.1029/2010JA015989

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DOI： 10.1029/2011JA016487

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DOI： 10.1029/2010JA015988

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DOI： 10.1029/2009JA014676

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2009JA014924

Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/BF03352828

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2007GL030174

Language：English  

Language：English  

Language：English   Publishing type：Research paper (other academic)  

Language：English  

Language：English  

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.5636/jgg.49.21

Language：English   Publishing type：Research paper (scientific journal)  

Two basic but novel equations directly describing the generation of shear Alfvén and compressional waves in the inner magnetosphere filled with a cold magnetized plasma are derived. The shear Alfvén wave is characterized by the field-aligned current and the compressional wave by the compressional component of the magnetic field. Such a generation arises from the effects of inhomogeneous Alfvén speed and curvilinear field line. Around the magnetic equator, if the Alfvén speed is inversely proportional to a power of the geocentric distance, these effects have magnitudes of the same order and their signs are identical. Considered in the present study is a situation that the earthward propagating compressional wave is launched from a large scale oscillating current wedge centered at midnight and symmetric about the magnetic equator. Then, it is found that the field-aligned current excited around the equator by the compressional wave has opposite senses in direction in the northern and southern hemispheres, in the pro- and post-midnight sectors as well as just inside the plasmapause and in its surrounding regions. As a result of the excitation of shear Alfvén wave, two types of oscillations appear on a field line: One is a forced oscillation and the other is an eigenoscillation. Although a modulation of the compressional wave may be caused locally (or microscopically) around the equator by the eigenoscillation of field line, the modulation can be globally (or macroscopically) neglected. So far as the propagation along the source longitude (source-earth line) around the equator is concerned, the coupling between compressional and shear Alfvén waves can be almost neglected and so one-dimensional response of the inner magnetosphere around the equator plays a significant role in the compressional oscillation.

DOI： 10.5636/jgg.48.1451

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

Publisher：Space Weather  

The ionosphere over Iran is located on the upper edge of equatorial ionization anomaly (EIA). The Equatorial Electrojet (EEJ) as the proxy of temporal evolution of the EIA is explored using the MAGDAS stations near the magnetic equator during quiet and active geomagnetic conditions. The possible impact of EIA on Total Electron Content (TEC) over Iran is investigated. Analyzing data from 140 stations over 7 months, it is found that EEJ influences TEC and its latitudinal penetration. During geomagnetically active days, EEJ's behavior and TEC's latitudinal variations are investigated. Diurnal EEJ patterns and counter electrojets (CEJ) are analyzed, alongside solar wind timing effects on EEJ and TEC using data from stations in Brazil, Peru, the Philippines, and Sri Lanka. Statistical correlations between maximum TEC and parameters extracted from the daily EEJ profile, including EEJ (Formula presented.), integrated EEJ (IEEJ), and IEEJ (Formula presented.) —highlight Iran's position at the EIA's upper edge, indicating high susceptibility to equatorial dynamics. In addition, the Rate of Total Electron Content Index (ROTI) has been analyzed under geomagnetic active conditions. The results demonstrate that ROTI exhibits good agreement with TEC in terms of latitude penetration and the detected gradient in TEC. Employing Artificial Neural Networks (ANN) for local TEC prediction, Iran is segmented into eight regions based on GNSS receiver distribution. Each region's ANN model, trained during the quiet geomagnetic condition, assesses predictability and accuracy. The ANN model demonstrates reliable local TEC forecasting and confirms the direct impact of equatorial dynamics on Iran's ionosphere.

DOI： 10.1029/2024SW004032

Scopus

Publisher：Atmosphere  

Ionospheric scintillation is a pressing issue in space weather studies due to its diverse effects on positioning, navigation, and timing (PNT) systems. Developing an accurate and timely prediction model for this event is crucial. In this work, we developed two machine learning models for the prediction of ionospheric scintillation events at the equatorial anomaly during the maximum and minimum phases of solar cycle 24. The models developed in this study are the Random Forest (RF) algorithm and the eXtreme Gradient Boosting (XGBoost) algorithm. The models take inputs based on the solar wind parameters obtained from the OMNI Web database from the years 2010–2017 and Pc5 wave power obtained from the Bear Island (BJN) magnetometer station. We retrieved data from the Scintillation Network and Decision Aid (SCINDA) receiver in Egypt from which the S4 index was computed to quantify amplitude scintillations that were utilized as the target in the model development. Out-of-sample model testing was performed to evaluate the prediction accuracy of the models on unseen data after training. The similarity between the observed and predicted scintillation events, quantified by the R2 score, was 0.66 and 0.74 for the RF and XGBoost models, respectively. The corresponding Root Mean Square Errors (RMSEs) associated with the models were 0.01 and 0.01 for the RF and XGBoost models, respectively. The similarity in error shows that the XGBoost model is a good and preferred choice for the prediction of ionospheric scintillation events at the equatorial anomaly. With these results, we recommend the use of ensemble learning techniques for the study of the ionospheric scintillation phenomenon.

DOI： 10.3390/atmos15101213

Web of Science

Scopus

Publisher：Earthquake Science  

Among electromagnetic methods of short-term earthquake prediction, an approach is being actively developed based on the phenomenon of magnetic ultra-low-frequency (ULF) power depression occurring a few days before an earthquake. In particular, a nighttime geomagnetic power depression in the band 0.03–0.05 Hz was observed approximately 5 days before the catastrophic Tohoku 2011 earthquake. To verify the reliability of this method, we performed an extended analysis using data from magnetometer arrays JMA, MAGDAS, PWING, and INTERMAGNET. The selected stations included sites close to the epicenter (<300 km) and remote points (∼10000 km). The band-integrated spectral power of nighttime magnetic noise decreased significantly from March 6–9, several days before the earthquake. However, such variations occur simultaneously not only at nearby stations but also at distant stations. During this event, the ULF power depression was caused by low global geomagnetic activity, as evidenced by the planetary index SME. Thus, the depression of geomagnetic ULF noise cannot be considered a reliable short-term precursor.

DOI： 10.1016/j.eqs.2024.06.003

Web of Science

Scopus

Publisher：Research in Astronomy and Astrophysics  

A geomagnetic storm is a global disturbance of Earth's magnetosphere, occurring as a result of the interaction with magnetic plasma ejected from the Sun. Despite considerable research, a comprehensive classification of storms for a complete solar cycle has not yet been fully developed, as most previous studies have been limited to specific storm types. This study, therefore, attempted to present complete statistics for solar cycle 24, detailing the occurrence of geomagnetic storm events and classifying them by type of intensity (moderate, intense, and severe), type of complete interval (normal or complex), duration of the recovery phase (rapid or long), and the number of steps in the storm's development. The analysis was applied to data from ground-based magnetometers, which measured the Dst index as provided by the World Data Center for Geomagnetism, Kyoto, Japan. This study identified 211 storm events, comprising moderate (177 events), intense (33 events), and severe (1 event) types. About 36% of ICMEs and 23% of CIRs are found to be geoeffective, which caused geomagnetic storms. Up to four-step development of geomagnetic storms was exhibited during the main phase for this solar cycle. Analysis showed the geomagnetic storms developed one or more steps in the main phase, which were probably related to the driver that triggered the geomagnetic storms. A case study was additionally conducted to observe the variations of the ionospheric disturbance dynamo (Ddyn) phenomenon that resulted from the geomagnetic storm event of 2015 July 13. The attenuation of the Ddyn in the equatorial region was analyzed using the H component of geomagnetic field data from stations in the Asian sector (Malaysia and India). The variations in the Ddyn signatures were observed at both stations, with the TIR station (India) showing higher intensity than the LKW station (Malaysia).

DOI： 10.1088/1674-4527/ad5b34

Web of Science

Scopus

DOI： 10.35848/1347-4065/ad6659

Web of Science

Language：English  

DOI： 10.4049/jimmunol.2300450

Web of Science

PubMed

Publisher：Journal of Atmospheric and Solar-Terrestrial Physics  

Pc5 geomagnetic pulsations can accelerate electrons in the radiation belts, which can pose adverse threats to both astronauts and satellites in space. The estimation of Pc5 waves in space is crucial to radiation belt dynamics studies and will help mitigate these challenges. Here, we explore the advantages of the Feed-forward Neural Network (FFNN) and Random Forest (RF) algorithm for effective estimation of Pc5 geomagnetic pulsations observed in space at geostationary orbit during solar cycle 23. The dataset used in this study is the vector magnetic field measurements retrieved from the Geostationary Operational Environmental Satellite-10 (GOES-10) and the solar wind parameters: Bz and Vx component of the solar wind in the Geocentric Solar Ecliptic (GSE) coordinate system, proton density, flow pressure, and plasma beta obtained from the OMNI Web database during part of solar cycle 23. Pc5 geomagnetic pulsations were extracted from the toroidal component of the magnetic field time series using a bandpass Butterworth filter. The continuous wavelet transform (CWT) was utilized to study the characteristics of the extracted wave in the time-frequency domain for its validation. The validated Pc5 events were used as the target in the model's development, with the solar wind parameters as the inputs. In addition to the solar wind parameters, we included an attribute of the magnetic field time series as an input variable in the model. The dataset is carefully divided to ensure effective training and testing of the models. Finally, we trained both models using the same inputs and targets and explored their estimation abilities. The model was tested during the maximum, descending, and minimum phases of solar cycle 23. Both the FFNN and RF models have a similar estimation, with average cross-correlation score (R) values of 0.74 and 0.73 and corresponding average root mean squared error (RMSEs) of 0.16 nT and 0.67 nT, respectively. The model was deployed to investigate the response of Pc5 waves during three storm days in each testing year. The machine learning (ML) model outputs showed good coherence with the observed Pc5 waves. To validate the models, we studied the correlation between the estimated Pc5 events with the Kp index, and a good correlation was seen to exist between both events. This validates the good performance of the developed models. This work will aid in the study of radiation belt dynamics and the construction of electron depletion regions in the radiation belt.

DOI： 10.1016/j.jastp.2024.106258

Scopus

Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

Abstract

Starting from 29 January 2022, a series of solar eruptions triggered a moderate geomagnetic storm on 3 February 2022, followed subsequently by another. Despite the typically minimal impact of unintense storms on space technology, 38 out of the 49 Starlink satellites underwent orbital decay, re‐entering Earth's atmosphere. These satellite losses were attributed to enhanced atmospheric drag conditions. This study employs numerical simulations, utilizing our test particle simulation code, to investigate the dynamics of the inner radiation belt during the two magnetic storms. Our analysis reveals an increase in proton density and fluxes during the transition from the recovery phase of the first storm to the initial phase of the second, primarily driven by intense solar wind dynamic pressure. Additionally, we assess Single Event Upset (SEU) rates, which exhibit a 50% increase in comparison to initial quiet conditions.

DOI： 10.1029/2023SW003789

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Language：English  

DOI： 10.1038/s41598-024-65420-7

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PubMed

DOI： 10.1016/j.jcrysgro.2023.127553

Web of Science

Language：Others   Publishing type：Research paper (scientific journal)  

This paper investigates the ionospheric responses to the February and April 2023 geomagnetic storms using Total Electron Content (TEC) derived from the 10 Global Navigation Satellite System (GNSS) stations at the transition of low to mid-latitudes (Approx. 20 ∼ 30°N) across different longitudes in the American and Asian sectors. Significant variations in both sectors were recorded during the recovery phase and were mainly attributed to the Prompt Penetration Electric Field (PPEF), Disturbance Dynamo Electric Field (DDEF) and the thermospheric neutral composition changes as O/N2 depletion. Similarly, the American and Asian sectors showed TEC enhancements, primarily attributed to the PPEF, during the main phase of the April storm. The negative TEC variations during the recovery phase were observed due to the DDEF and changes in O/N2. In the Asian sector, positive and negative variations were recorded over Pakistan and China, respectively, during the main phase of the April storm. These variations resulted in high and low concentrations of the O/N2 ratio due to Magnetosphere-Ionosphere-Thermosphere coupling.

DOI： 10.1016/j.asr.2023.12.039

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Language：English   Publisher：ALife Robotics Corporation Ltd.  

Measuring the altitude distribution of electron density in the upper atmosphere, known as the ionosphere, using HighFrequency radio wave reflections often causes the low signal-to-noise ratio of ionospheric echoes due to radio frequency interference. We propose a model for converting low-signal-to-noise-ratio ionospheric echo video images (Ionogram) into noise-reduced images using image processing techniques, for tracing the ionospheric echoes from Ionogram. The proposed method consists of three processing parts: noise removal optimized for individual Ionogram images, extraction of ionospheric echoes by penalized background subtraction technique, and fine-tuning of ionospheric echo signals using a minimum spanning tree algorithm. The proposed model successfully reproduces fine Ionograms with 98% recall and 99% precision.

DOI： 10.5954/icarob.2024.gs5-3

CiNii Research

DOI： 10.1016/j.jcrysgro.2023.127550

Web of Science

Language：Others   Publishing type：Research paper (scientific journal)  

The physical destruction and fatalities caused by earthquake events has compelled scientists to develop a method for predicting Earthquakes. It is almost impossible to detect earthquake events due to limited seismometer sensitivity; therefore, a non-seismological predictor was established by using the Ultra-Low Frequency (ULF) magnetic field as a potential earthquake precursor. ULF waves respond to magnetic activity that are transferred to Earth by solar winds, and become ultimately linked to earthquake events. The statistical correlation analysis is used between ULF Pc4 and Pc5 pulsation, solar wind parameters; IMF- component (Bz), solar wind speed (Vsw), solar wind pressure (Psw), solar wind input energy (IEsw), and near-equator geomagnetic storm (SYM/H ). Through a multiple regression modelled approach, the relationship between solar wind (SW) parameters (IMF-Bz, Vsw, Psw, IEsw) and near-equator geomagnetic index (SYM/H ) with ULF wave pulsations (Pc4 - Pc5) prior to an earthquake (EQ) event (magnitude, M = 3.0–6.0, depth, d < 100 km, epicentre distance from magnetometer station, r < 100 km) was determined. The solar wind and geomagnetic index parameters were obtained from OMNIWeb, where ULF pulsations (Pc4 - Pc5) were computed from the magnetometer Davao station (Philippines) (7.00oN, 125.40oE) located in a low latitude region. The ULF Pc5 band demonstrated the best fit for the ULF earthquake precursor model in relation to solar wind parameters (Vsw, Psw) and geomagnetic index (SYM/H ) with R2 and R2-adjusted values of (R2 =0.5011, R2-adj = 0.4940). The Vsw, Psw and SYM/H are major factors that contribute to the emission of ULF Pc5 prior to an earthquake, as determined by the stepwise regression method. This ULF earthquake precursor model is intended to address the problem seismologists face when predicting seismic events by assisting non-seismologists in locating the most effective EM-ULF wave bands in solar-terrestrial activities for detecting seismic events.

DOI： 10.1016/j.asr.2023.10.036

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Publishing type：Research paper (international conference proceedings)  

This study elucidates the development of the global three-dimensional current system from polar to equatorial regions during substorms. We extracted 50 cases from 1934 isolated substorms between 2006 and 2013. These 50 cases met two criteria: the electric field was calm for 1 h before the substorm, and clear electric field fluctuations were observed during substorm onset. We compared the 210 MM and mid-latitude magnetic field data to capture each event's distribution and temporal evolution of the substorm current wedge. Additionally, we captured the electric field response using the mid-latitude Paratunka station. The results revealed that the electric field amplitude was proportional to the SuperMAG aurora electrojet index magnitude (correlation coefficient = 0.67). In the central region of the substorm current wedge (SCW), predominantly westward electric fields were observed between the upward and downward field-aligned currents (FACs) (i.e., among 12 cases, wherein the observation points were at the center of the SCW, 10 showed westward electric fields). Moreover, a tendency for larger amplitudes of these westward electric fields was observed at the SCW center. This may reflect the projection of the primary potential formed by the charges injected into the upward and downward FAC regions on the ionosphere. Contrarily, a tendency for eastward electric fields was observed near the upward FAC of the SCW (i.e., among 24 cases, wherein the observation points were near or slightly inside the upward FAC, 14 showed eastward electric fields), which might be due to the twisting of the potential distribution associated with Hall polarization.

DOI： 10.1007/978-981-97-0142-1_7

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Publishing type：Research paper (international conference proceedings)  

It is well known that the geomagnetic field exhibits consistent diurnal, seasonal, and solar cycle fluctuations. In this paper, the seasonal variations of the quiet day (Sq) of the geomagnetic field in the recent solar cycle were obtained to characterise the profiling behaviour of the geomagnetic field using the horizontal component (H-component) at Langkawi. Long-term data analysis was limited to Magnetic Data Acquisition System (MAGDAS) data from 2011, 2012, 2013, 2016, and 2018. It was discovered that the seasonal variations of the geomagnetic field component during Sq demonstrated Langkawi as an equatorial station where the horizontal component of the geomagnetic field, MSq(H), peaked during the equinox for most of the year. The value is comparable to the predicted value by the model of the International Geomagnetic Reference Field (IGRF) at 41,794 nT. This information can be used to improve the accuracy of geomagnetic models and predictions, as well as gain a better understanding of the regular variations of Sq in Langkawi, one of equatorial observatories in Southeast Asia.

DOI： 10.1007/978-981-97-0142-1_12

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Publishing type：Research paper (international conference proceedings)  

During solar storms, conductivities in Earth’s ionospheric regions become more enhanced. This phenomenon produces effects on Earth’s current systems to which emissions of solar radiation largely contribute. Such radiations are analyzed as short timescale variations of the X-ray and EUV fluxes. This was observed for the two X- and three M-class solar flares on 17, 20, and 21 April 2022. All of which are geomagnetically quiet days with nominal Kp, Hp, and Dst indices. Magnetic responses were observed from magnetometers in the Philippines, located in the low-latitude (MUT) and near-equatorial (DAV) stations. These coexisting variations observed with Earth’s magnetic field are referred to as magnetic crochets. Measurements also showed that solar flare effects (Sfe) are more pronounced near the equator, where high conductivity generates more variations in Earth’s magnetic fields. Yet, the largest variations were not consistently observed for the strongest flares. At MUT, manifest variations in Hsfe (horizontal) and Zsfe (downward) were aligned with the X1.1 and M1.89 flares on day 17. Variations are generally homogeneous on days 20 and 21. Meanwhile, the largest variations at DAV were found during the M9.7 flare on day 21. It is inferred that increases in Hsfe remain greater than in Zsfe at both stations. Fluctuations in Hsfe are nonetheless more prolonged and heightened at DAV station.

DOI： 10.1007/978-981-97-0142-1_9

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Publishing type：Research paper (scientific journal)   Publisher：Instituto Nazionale di Geofisica e Vulcanologia, INGV  

Fluctuations in Solar Wind (SW) and Interplanetary Magnetic Field (IMF) significantly affect the Geomagnetic Field (GF) measurements particularly during extreme space weather events. The current study investigates the variations of horizontal (H), vertical (Z) geomagnetic components under quiet and disturbed IMF and solar conditions as well as the effect of underground conductivity on the stationary geomagnetic measurements in Japan. Results of data analysis show that the response of the GF to IMF and solar parameters fluctuations is variable. The H- and Z-components were in good harmony with high visual correlation along a latitudinal profile across Japan during quiet times. On the other hand, during the disturbed times related to a Coronal Mass Ejection (CME) launched on 13 May 2005, the GF components varied with the disturbance of IMF and solar parameters. The H-components showed highly correlated variations with a significant reduction along the examined profile due to intensified ionospheric currents, while the Z-components recorded in the northern part of Japan showed abnormal daily variations pattern (positive daily variations) with an enhanced amplitude which is opposite to the normal behavior of daily variations recorded in the central and southern parts of Japan (negative daily variations). The observed enhanced and abnormal daily variation of Z-components in north Japan, which we consider a remarkable observation here, is possibly linked with underground conductivity anomaly in this region.

DOI： 10.4401/ag-9021

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Publisher：IEEE Symposium on Wireless Technology and Applications, ISWTA  

Geomagnetic storms impact communication technology by disturbing the ionosphere, affecting GPS signal propagation, and causing navigation errors. These storms also induce voltages in long conductors such as communication cables, power lines, and pipelines through geomagnetically induced currents (GICs), leading to potential disruptions. This study addresses the gap in understanding geomagnetic field variations in low-latitudes, where infrastructure is less equipped for GIC disruptions. Furthermore, limitations in the availability of magnetic field components often necessitate the use of dB/dt as a GIC proxy for this region. This study aims to assess the relationship between the rate of change of the total magnetic field (dB/dt) and the horizontal magnetic field component (dH/dt) across different latitudes during the geomagnetic storm of 22-23 June 2015. Utilizing data from high (Narsarsuaq, Greenland), mid (Boulder, USA), and low (Alibag, India) latitude stations through correlation, cross-correlation, and linear regression analyses. The results reveal significant latitude dependent differences with strong correlations at mid and low latitudes. A strong linear correlation between dB/dt and dH/dt was observed, particularly at mid and low-latitudes. Cross-correlation analysis reveals synchronous responses at zero lag, indicating highly predictable relationships at lower latitude regions. Regression analysis demonstrates greater predictability of dB/dt and dH/dt at lower latitudes than at higher latitudes. These findings indicate that dB/dt is an effective proxy for GIC studies in low-latitude regions and enhance our understanding of geomagnetic impacts on infrastructure and highlight the importance of developing strategies tailored to different latitudes. This research contributes to the field by providing new insights into the use of dB/dt as a reliable measure for assessing GIC risks in low-latitude regions.

DOI： 10.1109/ISWTA62130.2024.10651826

Scopus

Publishing type：Research paper (international conference proceedings)  

Measuring the altitude distribution of electron density in the upper atmosphere, known as the ionosphere, using High- Frequency radio wave reflections often causes the low signal-to-noise ratio of ionospheric echoes due to radio frequency interference. We propose a model for converting low-signal-to-noise-ratio ionospheric echo video images (Ionogram) into noise-reduced images using image processing techniques, for tracing the ionospheric echoes from Ionogram. The proposed method consists of three processing parts: noise removal optimized for individual Ionogram images, extraction of ionospheric echoes by penalized background subtraction technique, and fine-tuning of ionospheric echo signals using a minimum spanning tree algorithm. The proposed model successfully reproduces fine Ionograms with 98% recall and 99% precision.

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Publisher：Proceedings of International Conference on Artificial Life and Robotics  

Measuring the altitude distribution of electron density in the upper atmosphere, known as the ionosphere, using High- Frequency radio wave reflections often causes the low signal-to-noise ratio of ionospheric echoes due to radio frequency interference. We propose a model for converting low-signal-to-noise-ratio ionospheric echo video images (Ionogram) into noise-reduced images using image processing techniques, for tracing the ionospheric echoes from Ionogram. The proposed method consists of three processing parts: noise removal optimized for individual Ionogram images, extraction of ionospheric echoes by penalized background subtraction technique, and fine-tuning of ionospheric echo signals using a minimum spanning tree algorithm. The proposed model successfully reproduces fine Ionograms with 98% recall and 99% precision.

Scopus

Publishing type：Research paper (international conference proceedings)  

Coronal mass ejection (CME) occurs in the Sun’s corona that travels and reaches Earth’s magnetosphere, and it can trigger a geomagnetic storm. In this work, we presented a case study of a geomagnetic storm triggered by CME and observed the presence of ionospheric disturbance dynamo (Ddyn) at the equatorial station. Our analysis utilized CME data from the SOHO/LASCO CME Catalog, which contains information such as CME speed, solar source location, digital data, and the CME LASCO/C2 movies. The Disturbance storm time (Dst) index calculated from ground-based magnetometer data describes the geomagnetic storm phases. On the other hand, the variation of the Ddyn at the equatorial region was derived from the H component of Earth’s magnetic field. Four stations at the dip equator cover the longitude sectors of Asia (DAV and TIR) and Africa (AAB and ILR). This study shows that halo CME on 4 August 2011 triggered intense geomagnetic storms (Dst = − 115 nT) on 6 August 2011. During this geomagnetic storm, after a few hours of Dst peak, the signature of Ddyn can be clearly observed in two stations of the African sector (ILR and AAB), while no presence of Ddyn in two other stations (TIR and DAV) in the Asian sector.

DOI： 10.1007/978-981-97-0142-1_23

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Language：Others   Publishing type：Research paper (scientific journal)  

The field of space weather research has witnessed growing interest in the use of machine learning techniques. This could be attributed to the increasing accessibility of data, which has created a high demand for investigating scientific phenomena using data-driven methods. The dataset, which is based on bibliographic records from the Web of Science (WoS) and Scopus, was compiled over the last several decades and discusses multidisciplinary trends in this topic while revealing significant advances in current knowledge. It provides a comprehensive examination of trends in publication characteristics, with a focus on publications, document sources, authors, affiliations, and frequent word analysis as bibliometric indicators, all of which were analysed using the Biblioshiny application on the web. This dataset serves as the document profile metrics for emphasising the breadth and progress of current and previous studies, providing useful insights into hotspots for projection research subjects and influential entities that can be identified for future research.

DOI： 10.1016/j.dib.2023.109667

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Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

Abstract

During a few solar energetic particle (SEP) events, solar protons were trapped within the geomagnetic field and reached the outer edge of the inner radiation belt. We reproduced this phenomenon by modeling the proton flux distribution at the Low‐Earth Orbit (LEO) for different geomagnetic conditions during solar particle events. We developed a three‐dimensional relativistic test particle simulation code to compute the 70–180 MeV solar proton Lorentz trajectories in low L‐shell range from 1 to 3. The Tsyganenko model (T01) generated the background static magnetic field with the IGRF (v12) model. We have selected three Dst index values: −7, −150, and −210 nT, to define quiet time, strong, and severe geomagnetic storms and to generate the corresponding inner magnetic field configurations. Our results showed that the simulated solar proton flux was more enhanced in the high‐latitude regions and more expanded toward the lower latitude range as long as the geomagnetic storm was intensified. Satellite observations and geomagnetic cutoff rigidities confirmed the numerical results. Furthermore, the LEO proton flux distribution was deformed, so the structure of the proton flux inside the South Atlantic Anomaly (SAA) became longitudinally extended as the Dst index decreased. Moreover, we have assessed the corresponding radiation environment of the LEO mission. We realized that, for a higher inclined LEO mission during an intense geomagnetic storm (Dst = −210 nT), the probability of the occurrence of the Single Event Upset (SEU) rates increased by 19% and the estimated accumulated absorbed radiation doses increased by 17% in comparison with quiet conditions.

DOI： 10.1029/2023SW003664

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J-GLOBAL

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DOI： 10.22541/essoar.170000392.22424750/v1

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Language：Others   Publishing type：Research paper (scientific journal)  

The solar surface activity produces space weather. Solar flares, coronal mass ejections (CMEs), and coronal holes are examples of solar activity phenomena that can compress the magnetosphere and cause a geomagnetic storm. Previous studies have indicated that these solar events disturb the near-Earth region. This study examines the behavior of the terrestrial geomagnetic field (H-component) and focuses on how the geomagnetic index (SYM/H) responds to solar wind parameters related to solar activity. Results showed that on September 9, 2017, a powerful geomagnetic storm (SYM/H = 200 nT) was observed that was brought on by powerful solar flares, CMEs, and coronal holes that happened on September 7 and 8, 2017, which generated significant alterations in the magnetosphere’s solar wind. On October 3 and 18, 2017, a moderate geomagnetic storm occurred, which resulted in a strong southbound situation with a high solar wind pressure that blasted high-density plasma due to CME associated with a coronal hole event into the magnetosphere. A moderate geomagnetic storm (SYM/H = 80 nT) on November 14, 2017, was triggered, according to findings, by a wider direction and high speed of CME with CIR event occurrence implies the accelerated large-scale solar wind that exacerbated the reconnection of the flowing interplanetary magnetic field into the inner magnetosphere. There were fewer injections of ions and energetic solar particles into the magnetosphere on December 12, 2017, which were thought to be a source of a weak geomagnetic storm(SYM/H = 49 nT). Additionally, the response of solar wind parameters and geomagnetic storm due to solar flare, CMEs and coronal holes to the modest drop in the ground geomagnetic field resulted in H-component reading at the RAN and DLT station. This study has contributed to the study of earthquake precursors in ultra-low frequency (ULF) emission with the effect of solar wind.

DOI： 10.1007/s12648-023-02721-z

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Studying Pc3-4 geomagnetic pulsations at equatorial and very low latitude regions is an important issue to understand their generation and propagation mechanisms. Pc3-4 amplitudes and their latitudinal dependency across the dip equator up to low latitudes (± 25°) are investigated using geomagnetic data simultaneously obtained by the MAGDAS/CPMN stations along the 210° Magnetic Meridian (MM) chain. Forty-five Pc3 events and thirty-two Pc4 events were selected for this study. Our results show a clear dependence of Pc3-4 amplitudes on geomagnetic latitudes. At the dip equator, most of the selected Pc3 events (~75%) showed an enhancement in amplitudes, while the rest (~25%) showed an attenuation. After that, the amplitudes decreased gradually by increasing latitudes. These results suggest mixed generation and propagation mechanisms for the equatorial and very low latitudes Pc3s. For better understanding, the Interplanetary Magnetic Field (IMF) and solar conditions are examined during the selected events. Results indicate that Pc3 events with enhanced amplitudes at dip equator are mainly occurred in daytime with no preference to IMF (magnitude and direction) and solar parameters, which suggests the ionospheric currents model as a generation and propagation mechanism for these events. While the attenuation observed in the other Pc3 events was associated with intense and abrupt fluctuations in the IMF and solar parameters, which in turn suggests the compressional wave model for generating these Pc3 events. On the other hand, these two models can explain the observed enhancement in the Pc4 amplitudes at the dip equator. Therefore, our obtained results clarified the origin of equatorial Pc3-4 pulsations.

DOI： 10.4401/ag-8979

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The east–west electric field and the characterized horizontal configuration of the geomagnetic fields around the equatorial region cause electron redistribution in the ionospheric bottomside F- region. This electric field E in turn causes the flow of current in a narrow band around this region called Equatorial Electrojet (EEJ) current. The paper discusses the robust least square modelling approach for modelling some selected ionospheric profile parameters below the maximum height of the F2 layer from the computed EEJ values at Jicamarca station (12°S, 76.9 °W) in the Southern American sector and Ilorin (8.50°N, 4.68°E) in the West African sector. The modelled parameters are the maximum electron density, NmF2, the maximum height, hmF2 and the thickness parameter, B0 of the F2- layer which were then compared with the recent ionospheric international standard model (IRI-2016). The proposed new model for ionospheric parameters based on ground-based magnetic field data at specific locations improved the model fit for hmF2 with RMSE value ∼ 30 km, an improvement to the IRI hmF2 model options. In addition, the derived NmF2 model performs poorly as compared to the IRI URSI and CCIR model options for NmF2. The model was however able to reproduce the temporal changes in the NmF2, for example, the semi-annual variation in the observational NmF2 value. The specific local features that were not fully reproduced in the IRI B0 model options can be seen in the derived model.

DOI： 10.1016/j.asr.2023.04.040

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This study investigated the simultaneous effects of solar flares (SFs) on both the D and E layers of Earth’s ionosphere. The analysis focused on the M and X-class SFs that occurred during the 24th solar cycle as these two classes of SFs are known to produce significant effects on Earth’s environment, particularly during the daytime period. The data utilized to detect the SF events in this study were ground-based magnetometer data from the equatorial regions. Effects of the selected SF events on the E layer were investigated based on the EUEL index constructed using the geomagnetic data. Meanwhile, the changes in the strength of radio VLF signals in the D ionospheric layer during the selected SF events were monitored using Sudden Ionospheric Disturbance (SID) data. Two case studies were performed which consisted of four SF events from a total of 23 events that were detected by geomagnetic data during the period of study. Further analysis on the selected SF events showed the common effects of SFs on the D layer, which is the increment on the VLF signal measured from the SID stations although a different response was detected in the EUEL index variations. This indicates that the VLF signal always shows an increment even though a decrement in the ionization of the E layer occurs as a result of the SF events. The difference in responses could be attributed to the distinct changes in electron density of both layers during the SF occurrence. Further studies are needed to elucidate the underlying mechanism responsible for this unique response, utilizing appropriate parameters such as total electron content, as well as the electron density data to thoroughly analyze the ionospheric response during SF events.

DOI： 10.17576/jsm-2023-5208-11

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Geomagnetic micropulsations are ultra-low frequency (ULF) signals observed in the magnetosphere as well as on the ground. These signals offer us an effective means to study the coupling of the magnetosphere-ionosphere processes in the space field. The most prominent observed type of such ULF waves is the Pc5 pulsations (with a frequency range of 1–7 mHz), known to have their maximum amplitude in the auroral oval. The low magnitude of Pc5 signals withstands against distinguishing them from the background noise. This study presents a machine learning approach for the automatic detection of geomagnetic Pc5 pulsations in the auroral zone using artificial neural networks (ANN) guided by discrete wavelet transform. Our ANN algorithm is validated and tested using a huge amount of datasets of auroral ground-based geomagnetic records from the Svalbard network during the two solar cycles 23 and 24. The wavelet-based coherence was used to determine the signal's consistency detected by the magnetometer stations of the Svalbard network; since they are sensitive to all sorts of space wave-related phenomena that left their footprint on the magnetic field time series. The Daubechies wavelet transform was utilized to classify and extract Pc5 signals from the artificial noise and the results are correlated with the geomagnetic pulsation records as detected by our ANN-based model. The ANN-based model showed a good correlation of an average of 98% for the different phases of the two studied solar cycles. The statistical regression analysis of the post-processed results yielded a high coefficient of determination of R2 = 0.9 and norms of residuals of 8–21 nT. The Pc5 events detected by the ANN-based algorithm during the two solar cycles showed a good correlation with the Kp index, which enables our model for space weather forecasting.

DOI： 10.1016/j.asr.2022.06.063

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This study presents the first results of a newly installed ground-based station Alex Magnetometer and Telluric Station (AMTS) located in Alexandria governorate in Egypt (geographic coordinate: 30° 51.68′ N, 29° 33.67′ E). The station consists of a fluxgate digital magnetometer and a two-channel digital Long Period Telluric Recorder (LPTR). The station commenced operation on October 12th, 2021, by providing real-time data of the geoelectric and geomagnetic field components. Despite the low solar activity, the AMTS detected several signatures of geomagnetic storms. An illustrative case study was conducted on the strong geomagnetic storm of November 4th, 2021. The magnetic field components recorded by the station demonstrated a prompt increase synchronized with the Sudden Storm Commencement (SSC) captured by the ACE satellite arriving at 19:42 UT on November 3rd, 2021. The three geomagnetic field components recorded by the AMTS during the storm were consistent with the nearby INTERMAGNET stations. The digital fluxgate magnetometer's high sampling frequency (400 Hz) and the LPTR with a sampling frequency (1 Hz), allowed us to capture all ULF pulsations. The structural pearl-shaped Pc1 pulsation was obtained in all phases of the geomagnetic storm with repetitive oscillations in the main storm phase. The wavelet analysis of micropulsations recorded at AMTS showed a high coherence with the nearby-four INTERMAGNET stations demonstrating high data integrity and reliability. The magnetometer and telluric measurements at the AMTS will fill the data gap in the northern section of Africa and allow us to study geoelectric and geomagnetic micropulsations in the region.

DOI： 10.1016/j.asr.2022.09.014

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DOI： 10.22541/essoar.168748458.80915597/v1

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

The presence of the dawn-to-dusk electric field of about 4 mV/m in the Jovian inner magnetosphere and its response to the enhancement of the solar wind dynamic pressure are still a mystery of the rotation-dominated Jovian magnetosphere. Previous studies have suggested that magnetosphere-ionosphere (M-I) coupling via Region 2-like (R2-like) field-aligned current (FAC) could be the origin of the Jovian dawn-to-dusk electric field. This study investigates whether the dawn-to-dusk electric field is formed from this scenario by using a Jovian ionosphere model and a two-dimensional ionospheric potential solver. Our results show that the dawn-dusk asymmetry in the ionospheric potential form even at middle latitudes and that the dawn-to-dusk electric field is induced in the inner magnetosphere if the electric potential is mapped to the magnetospheric equatorial plane. Around the Io orbit, the calculated electric field strength for the ionosphere without meteoroid influx is too large, 200 mV/m at dawn and 88 mV/m at dusk. One of the solutions is to consider long-lived meteoric ions in the Jovian ionosphere, which reduce the electric field strength to 15 mV/m at dawn and 12 mV/m at dusk. The model also shows that the electric field strength increases with the intensity of R2-like FAC, consistent with its response to the solar wind dynamic pressure observed by the Hisaki satellite.

DOI： 10.1029/2022ja031248

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Language：English   Publisher：The Japanese Association of Rehabilitation Medicine  

<b>Objectives: </b>Increased long-term impairment is common among intensive care unit (ICU) survivors. However, predictors of activities of daily living (ADL) in ICU survivors are poorly understood. We aimed to focus on the trajectory of physical function and explore the clinical variables that affect ADL at hospital discharge.

<b>Methods: </b>We enrolled 411 patients admitted to the ICU from April 2018 to October 2020. Physical function was evaluated at ICU admission, ICU discharge, and hospital discharge. We assessed physical function (grip strength, arm and calf circumference, quadriceps thickness, and Barthel index). Patients were assigned to the high or low ADL group based on their Barthel index at discharge. Propensity score matching analysis was performed to minimize selection biases and differences in clinical characteristics.

<b>Results: </b>After matching propensity scores, 114 of the 411 patients (aged 65±15 years) were evaluated. The high ADL group showed better physical function at ICU discharge and hospital discharge than the low ADL group. An overall decreasing trend in muscle mass was observed over time; the rates of decline were lower in the high ADL group than in the low ADL group. The cutoff values for relative changes in calf circumference and quadriceps thickness to predict high ADL were −7.89% (sensitivity: 77.8%, specificity: 55.6%) and −28.1% (sensitivity: 81.0%, specificity: 58.8%), respectively.

<b>Conclusions: </b>The relative decreases in calf circumference and quadriceps thickness during hospitalization were lower in patients who maintained their ADL. Assessment of the trajectory of physical function can predict ADL status at hospital discharge among ICU survivors.

DOI： 10.2490/prm.20230010

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Other Link： https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-20K19447/

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The physical destruction and fatalities caused by earthquake events compelled scientists to develop Earthquake predictions. Due to limited seismometer sensitivity, it was impossible to detect earthquake events; therefore, non-seismological is established, which in Ultra Low Frequency (ULF). The study of electromagnetic waves (EM) in the Ultra-Low Frequency (ULF) range is a promising tool for investigating seismomagnetic effects that act as an earthquake precursor. This study analysed the ULF frequency range as a short-term earthquake precursor at a depth < 100 km and an epicentral distance < 100 km (distance from Cebu magnetometer station) measured using a ground magnetometer installed in Cebu (10.36°N, 123.91°E), in the Philippines. This study also intended to determine the emission of magnetic pulsation (Pc4 and Pc5), solar wind parameters and near equatorial geomagnetic storms (SYM/H) in low latitude regions prior to an earthquake event. Findings show that the most evident ULF that acts as a potential earthquake precursor was at a frequency range of Pc5 (1.7-6.7 mHz) compared to Pc4 (6.7-22 mHz). It also shows that high solar wind changes and geomagnetic storms respond to the emission of ULF magnetic pulsations (Pc4 and Pc5) prior to earthquake events at low latitudes. Thus, it can be concluded that magnetic pulsations are signatures that indicate the probability of short-term earthquakes precursor.

DOI： 10.32802/ASMSCJ.2023.1189

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Pc5 geomagnetic pulsations are ultra-low frequency (ULF) waves whose period lies within 150–600 s. Their detection is crucial for accurate space weather modelling, monitoring, and analysis. Identification of these pulsations using manual approaches is difficult and time-consuming because of the smaller magnitudes and the limited durations within which they occur. To overcome this challenge, we propose a robust Cascade Forward Neural Network (CFNN) model combined with the wavelet technique for automatically detecting Pc5 events from satellite datasets observed at geostationary orbits. The dataset used in this study is the magnetic field vector measurements retrieved from the Geostationary Operational Environmental Satellite-10 (GOES-10) from 2000 to 2009. Pc5 geomagnetic pulsations were extracted from the toroidal component of the field perturbation using a bandpass Butterworth filter. Continuous wavelet transform (CWT) analysis using the mother Morlet wavelet was utilized to validate the integrity of the extracted signal in the time–frequency domain. The extracted Pc5 signal was decomposed into details and approximations using Daubechies wavelet transform to separate the intelligible signal from the incoherent noise that left their trace on the magnetic field time series. The detail signal was subjected to denoising using the heuristic Stein Unbiased Risk Estimate (SURE) approach with soft thresholding to obtain the denoised Pc5 events. The denoised Pc5 events were utilized as the target in the machine learning whereas the inputs were obtained from 5-dimensional space transformation of the toroidal component of the time series. The developed algorithm performed well and demonstrated a detection accuracy of 80 % and a Root Mean Square Error (RMSE) of 0.13 nT indicating a high performance in detecting Pc5 events. For effective validation of the model, Pc5 events detected by our model were correlated with the Kp index and the amplitude of the Pc5 events observed at geostationary orbit. A good correlation was obtained in both cases, making our model a practical and preferred choice for Pc5 pulsation detection in contrast to conventional frequency analysis tools which take much time for signal processing on large data sets.

DOI： 10.1016/j.asr.2023.11.001

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DOI： 10.2113/RGG20214362

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DOI： 10.3389/fcimb.2022.925444

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PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

The intensity of the equatorial electrojet (EEJ) shows temporal and spatial variability that is not yet fully understood nor accurately modeled. Atmospheric solar tides are among the main drivers of this variability but determining different tidal components and their respective time series is challenging. It requires good temporal and spatial coverage with observations, which, previously could only be achieved by accumulating data over many years. Here, we propose a new technique for modeling the EEJ based on principal component analysis (PCA) of a hybrid ground-satellite geomagnetic data set. The proposed PCA-based model (PCEEJ) represents the observed EEJ better than the climatological EEJM-2 model, especially when there is good local time separation among the satellites involved. The amplitudes of various solar tidal modes are determined from PCEEJ based tidal equation fitting. This allows to evaluate interannual and intraannual changes of solar tidal signatures in the EEJ. On average, the obtained time series of migrating and nonmigrating tides agree with the average climatology available from earlier work. A comparison of tidal signatures in the EEJ with tides derived from neutral atmosphere temperature observations show a remarkable correlation for nonmigrating tides such as DE3, DE2, DE4, and SW4. The results indicate that it is possible to obtain a meaningful EEJ spectrum related to solar tides for a relatively short time interval of 70 days.

DOI： 10.1029/2022JA030691

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI  

Studies on counter-electrojet currents (CEJ) using ground data revealed that this current could occur simultaneously among locations that are less than 30 degrees longitude apart. In our work, the symmetricity of CEJ variation between the west and east of Southeast Asia, separated by similar to 25 degrees, was preliminarily examined according to its types: morning (MCEJ) and afternoon (ACED. Since most of the past studies had overlooked the occurrence after dusk, the monitoring period was also extended from 18:00 to 21:00 LT, namely, the post-sunset depletion (PSD). The magnetometer station in Davao, Philippines (DAV) and Langkawi, Malaysia (LKW) were chosen to represent the east and west parts. The EEJ index (i.e., EUEL) over the periods of the solar cycle 24 (2008-2018) was utilized specifically during magnetically quiet days (Kp < 3). As the result, both parts symmetrically showed that MCEJ and ACEJ were positively and negatively correlated with the F10.7 index. Contrarily, MCEJ and ACEJ were asymmetrically prominent in the east and west. CEJ types also varied symmetrically with the season, especially for MCEJ and ACEJ (at high level), prominent during Equinox and J-solstice. Post-sunset depletion (PSD) in both parts was symmetrically solar activity independent, as no correlation with the F10.7 index was observed in the extended observation. PSD that varied symmetrically with season was also solar activity independent, except in the east during Equinox, where it was negatively correlated with the F10.7 index. Our finding also revealed that PSD was prominent during Equinox, except for the high level in the west part.

DOI： 10.3390/app12147138

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Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2022gl098105

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2022GL098105

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The equatorial ionosphere endured plasma density irregularities during a geomagnetic storm on 21–22 December 2014. To understand the underlying mechanism, we analyzed the rate of the total electron content change (ROTI) data obtained from a global navigation satellite system, along with solar wind, interplanetary magnetic field (IMF), geomagnetic indices, Jicamarca incoherent scatter radar, and magnetometer data. The results indicate that the ROTI enhancement related to plasma density irregularities (plasma bubbles) occurred three times in the equatorial and low latitude regions of the American sector during the geomagnetic storm. The first, second, and third enhancements which have a longitudinal extent of ∼20° appeared in the post-sunset, pre-midnight, and post-midnight sectors, respectively. The second enhancement occurred during the recovery phase of the storm-time substorm even though the IMF remained southward. During this period, the direction of the dayside equatorial electrojet (EEJ) changed from eastward to westward, while the nightside upward plasma velocity at Jicamarca increased to 28.8 m/s. The response of the EEJ and upward ion drift implies that the westward and eastward electric fields were intensified on the dayside and nightside, respectively. Therefore, these results suggest that an over-shielding electric field penetrates the dayside/nightside equator simultaneously in association with a substorm recovery phase, and that the electric field generates plasma bubbles by the Rayleigh-Taylor instability mechanism. Plasma bubbles induced by the penetration of an over-shielding electric field due to substorm activity have not previously been reported.

DOI： 10.1029/2021JA030240

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Effect of Meteoric Ions on Ionospheric Conductance at Jupiter
Ionospheric Pedersen and Hall conductances play significant roles in electromagnetic coupling between the planetary ionosphere and magnetosphere. Several observations and models have suggested the existence of meteoric ions with interplanetary origins in the lower part of Jupiter’s ionosphere; however, no models have considered the contributions of meteoric ions to ionospheric conductance. This study is designed to evaluate the contribution of meteoric ions to ionospheric conductance by developing an ionospheric model combining a meteoroid ablation model and a photochemical model. We find that the largest contribution to Pedersen and Hall conductivities occurs in the meteoric ion layer at altitudes of 350–600 km due to the large concentration of meteoric ions resulting from their long lifetimes of more than 100 Jovian days. Pedersen and Hall conductances are enhanced by factors of 3 and 10, respectively, in the middle- and low-latitude and auroral regions when meteoric ions are included. The distribution of Pedersen and Hall conductances becomes axisymmetric in the middle- and low-latitude regions. Enhanced axisymmetric ionospheric conductance should impact magnetospheric plasma convection. The contribution of meteoric ions to the ionospheric conductance is expected to be important only on Jupiter in our solar system because of Jupiter’s intense magnetic and gravitational fields.

DOI： 10.1029/2022JA030312

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2022JA030312

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

We use the in-situ observations of DMSP and SWARM satellites to report the changes of the topside ionospheric electron temperature during the October 2016 storm. Electron temperature in the afternoon sector dramatically increases in low latitudes in the recovery phase of the storm. Furthermore, the temperature enhancements have an obvious dependence on longitude and are mainly centralized around 100°–150°E in different satellite observations. The temperature enhancements attain more than 2,000 K at 840 km and 1,500 K at 450 km around the magnetic equator. The decrease in the electron-ion collision cooling rate, resulting from the lessened topside electron density, could not fully explain the temperature enhancement. At the same time, the electron densities in crests of the equatorial ionization anomaly are suppressed drastically at 100°–150°E, which cause a less heat conduction effect from the equatorial topside ionosphere to low altitudes via magnetic field lines and heat the topside ionospheric electron temperature. Further analysis indicates that dayside westward disturbance dynamo electric field presents a significant longitude structure and is a primary driver for the topside ionospheric temperature enhancement during the storm.

DOI： 10.1029/2022JA030278

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

The solar quiet (Sq) ionospheric current variations exhibit spatial and temporal patterns that can be identified by the prevailing eigenmodes based on the empirical orthogonal function (EOF) analysis. In this study, the Sq current function over the American and European/African sectors are derived using ground magnetometer data from 2006 to 2019 based on the spherical harmonic analysis technique. Subsequently, we decomposed the Sq current function into eigenmodes by applying the EOF analysis, where the first three eigenmodes capture 96% of the overall Sq current variance. Additionally, these eigenmodes are utilized to model the Sq current function and compare its properties between the two longitudinal sectors. We observed that the EOF model could reconstruct the observed Sq current function with the first three eigenmodes in both longitudinal sectors. Moreover, the EOF model unveils a clear association of the Sq current function with several driven features, such as magnetic latitude, local time, season, and solar activity. Both longitudinal sectors had comparable Sq current patterns under varying solar activity, while their amplitudes varied. Besides, the newly developed model could reproduce a refined Sq current variability over the two longitudinal sectors as long as the observed Sq variations have sufficient duration. Our EOF model shows that the variations of the Sq current function with solar activity can be explained by the first three eigenmodes, which could be used as a basis for further numerical modeling of the Sq current variations.

DOI： 10.1029/2021JA029903

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

Data imputation studies include reconstruction or estimation of imperfect data gaps caused by system sensing failure, and non-responsive data transmission remains an open issue. In space weather applications, imputation of ground electromagnetism is significant in capturing the complex interaction of sun–earth prior to the subsequent analysis of the space weather effects. Key contributions to the demonstration of supervised machine learning (ML) imputation approach with artificial neural network, K-nearest neighbour, support vector regression (SVR), and General Regression Neural Network (GRNN) for MAGDAS-9 ground electromagnetism dataset have not yet been established. A total of 1,585,950 data points were analysed with supervised ML models which included performance benchmark with statistical analysis namely zero value substitution, listwise deletion, mean substitution, and hot deck imputation. To achieve low reconstruction errors, different imputation models with hyperparameter tuned settings are varied, and computational time execution has been shown to contribute to imputation performance. Performance metrics measured by mean square error (MSE), mean absolute error (MAE),mean absolute percentage error (MAPE), and execution time respectively demonstrate the capability of SVR to perfectly impute missing data for all ground electromagnetism components at an average of 0.314 MSE, 0.738 MAPE, closeness to 0.510 MAE and 0.91-second at various percentage level of data missingness. A comparison with traditional imputation shows that the supervised ML with SVR model has improved imputation performance by up to 80% of data gap. The outcome of the proposed imputation will benefit space weather applications for event characterisation, which will cover a large number of missing data in the MAGDAS-9 dataset.

DOI： 10.1016/j.aej.2021.04.096

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

The thermospheric wind response to a sudden westward turning of the ion velocity at a high latitude was studied by analyzing data obtained with a Fabry-Perot interferometer (FPI; 630 nm), Dynasonde, and Swarm A & C satellites during a conjunction event. The event occurred during a geomagnetically quiet period (Kp= 0+) through the night, but some auroral activity occurred in the north. The collocated FPI and Dynasonde measured the thermospheric wind (U) and ionospheric plasma velocity (V), respectively, in the F region at the equatorward trough edge. A notable scientific message from this study is the possible role of thermospheric wind in the energy dissipation process at F-region altitude. The FPI thermospheric wind did not instantly follow a sudden V change due to thermospheric inertia in the F region. At a pseudo-breakup during the event, V suddenly changed direction from eastward to westward within 10 min. U was concurrently accelerated westward, but its development was more gradual than that of V, with U remaining eastward for a while after the pseudo-breakup. The delay of U is attributed to the thermospheric inertia. During this transition interval, U.V was negative, which would result in more efficient generation of frictional heating than the positive U.V case. The sign of U.V, which is related to the relative directions of the neutral wind and plasma drift, is important because of its direct impact on ion-neutral energy exchange during collisions. This becomes especially important during substorm events, where rapid plasma velocity changes are common. The sign of U.V may be used as an indicator to find the times and locations where thermospheric inertia plays a role in the energy dissipation process.

DOI： 10.1186/s40623-022-01710-6

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We have studied the radiation environment of LEO spacecraft when passing through the South Atlantic Anomaly (SAA) during the geomagnetic storm event of 15 May 2005. The 70-180 MeV proton flux information were numerically obtained from a simulation model of the inner radiation belt. The radiation analysis was consisted of two parts: the estimation of the Single Event Upset (SEU) rates and the absorbed radiation doses. One of the characteristics of the SAA at 800 km altitude during the recovery phase of the geomagnetic storm was the enhancement of its southern proton flux cell. It was found that the excess SEU rates and absorbed radiation doses could reach at least 200 % and 70 % respectively during the recovery phase in comparison to the initial phase of the geomagnetic storm. The estimated radiation results were in a good agreement with observations.

DOI： 10.1109/JRFID.2022.3163441

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Publisher：Journal of Mechanical Engineering  

This paper discusses geomagnetic field attempt modelling using an Artificial Neural Network (ANN). The local horizontal component of geomagnetic field data was collected on April 2011 (equinox) during a solar quiet day at recent solar cycle inclination-24 using the Magnetic Data Acquisition System (MAGDAS) in Langkawi, Malaysia, in the low latitude region. The calculated average values (mean) of the H component geomagnetic field variation during Equinox 2011 characterised the dominant geomagnetic field during that particular solar cycle. The difference in amplitude of maximum and minimum values shows a regular diurnal variation of the geomagnetic field during Sq in the low latitude region. The output training utilised these calculated mean values during the modelling attempt. Meanwhile, the input training utilised proton density, solar wind plasma speed, plasma flow pressure, and Interplanetary Magnetic Field (IMF) space data using Non-Linear Auto Regressive Input (NARX). The best modelling outputs were 3, 2, and 3 for input delay (nu), output delay (ny), and hidden layer size (h), respectively. Residual test and model fit analysis show an unbiased and high overlap between predicted and actual geomagnetic field average values, suggesting the model can potentially anticipate the geomagnetic field average during solar quiet in November (month of Equinox) on solar cycle inclination.

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This paper discusses geomagnetic field attempt modelling using an Artificial Neural Network (ANN). The local horizontal component of geomagnetic field data was collected on April 2011 (equinox) during a solar quiet day at recent solar cycle inclination-24 using the Magnetic Data Acquisition System (MAGDAS) in Langkawi, Malaysia, in the low latitude region. The calculated average values (mean) of the H component geomagnetic field variation during Equinox 2011 characterised the dominant geomagnetic field during that particular solar cycle. The difference in amplitude of maximum and minimum values shows a regular diurnal variation of the geomagnetic field during Sq in the low latitude region. The output training utilised these calculated mean values during the modelling attempt. Meanwhile, the input training utilised proton density, solar wind plasma speed, plasma flow pressure, and Interplanetary Magnetic Field (IMF) space data using Non-Linear Auto Regressive Input (NARX). The best modelling outputs were 3, 2, and 3 for input delay (nu), output delay (ny), and hidden layer size (h), respectively. Residual test and model fit analysis show an unbiased and high overlap between predicted and actual geomagnetic field average values, suggesting the model can potentially anticipate the geomagnetic field average during solar quiet in November (month of Equinox) on solar cycle inclination.

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Language：English  

<jats:title>Abstract</jats:title><jats:p>Although solar activity may significantly impact the global environment and socioeconomic systems, the mechanisms for solar eruptions and the subsequent processes have not yet been fully understood. Thus, modern society supported by advanced information systems is at risk from severe space weather disturbances. Project for solar–terrestrial environment prediction (PSTEP) was launched to improve this situation through synergy between basic science research and operational forecast. The PSTEP is a nationwide research collaboration in Japan and was conducted from April 2015 to March 2020, supported by a Grant-in-Aid for Scientific Research on Innovative Areas from the Ministry of Education, Culture, Sports, Science and Technology of Japan. By this project, we sought to answer the fundamental questions concerning the solar–terrestrial environment and aimed to build a next-generation space weather forecast system to prepare for severe space weather disasters. The PSTEP consists of four research groups and proposal-based research units. It has made a significant progress in space weather research and operational forecasts, publishing over 500 refereed journal papers and organizing four international symposiums, various workshops and seminars, and summer school for graduate students at Rikubetsu in 2017. This paper is a summary report of the PSTEP and describes the major research achievements it produced.</jats:p>

DOI： 10.1186/s40623-021-01486-1

Language：English  

The east–west component of magnetic field variation (∆D-component) at Davao station (Philippines, geomagnetic latitude: – 2.22˚N) are used to investigate the characteristics of the long-term Inter-Hemispheric Field-Aligned Currents (IHFACs) based on the time-series analysis from August 1998 to July 2020. Recent in situ satellite and ground-based observations have reported that dusk-side current polarity of IHFAC is often opposite to that of the noon IHFAC, being inconsistent with Fukushima's IHFACs model. We investigated the consistency of the dusk-side IHFAC polarity derived from the observations with the polarity expected from Fukushima’s IHFACs model and examined the solar cycle dependence of IHFACs. It was confirmed that the dusk-side IHFACs during June and December solstices flow in the same direction of the noontime IHFACs, which was consistent with the IHFAC polarities suggested by the Fukushima model. The dusk-side IHFACs around March and September–November months disagreed with the Fukushima model. The ∆D variations clearly showed seasonal asymmetry in the dawn and noon sectors, whereas the ∆D variations in the dusk sector demonstrated seasonal symmetry. Solar cycle dependence of IHFACs was exhibited in the dusk sector. For the dawn and noon sectors, the yearly peak-to-peak ∆D amplitude in the later solar cycle SC24 decreased by about 35&#37; in comparison with the earlier solar cycle SC23. In contrast, the dusk-side yearly peak-to-peak ∆D amplitude increased by about 200&#37;. The dusk-side IHFAC yearly amplitude tended to be in inverse proportion to solar activity. [Figure not available: see fulltext.]

DOI： 10.1186/s40623-021-01481-6

Language：Others   Publishing type：Research paper (other academic)  

DOI： 10.1088/1755-1315/880/1/012010

Language：English   Publishing type：Research paper (scientific journal)  

Empirical Modeling of Ionospheric Current Using Empirical Orthogonal Function Analysis and Artificial Neural Network
Given the potential importance of solar quiet (Sq) ionospheric current in geomagnetic field modeling, it is vital to obtain accurate parameters characterizing its variations, particularly the spatial and temporal variations. In this paper, we derived the Sq current function based on the spherical harmonic analysis (SHA) technique using a 14-year (2006–2019) quiet geomagnetic field record over the American sector. The empirical orthogonal function (EOF) analysis was then applied to deduce temporal and spatial variations of the Sq current. It is observed that the first EOF mode of the Sq current function is dominated by solar activity, while the second and third EOF modes exhibit annual and semiannual variations, respectively. Also, the artificial neural network (ANN) model of Sq current function was constructed to validate the EOF model predictions. While the Sq current intensity predicted by the ANN model is underestimated by 2.83&#37;, the EOF model underpredicted the Sq current intensity by 1.92&#37; relative to the observation. The root mean square error (RMSE) of the EOF model is 0.64 kA. This RMSE is about 79&#37; smaller than that of the ANN model. In addition, both the EOF and ANN models capture the variation of the total Sq current (Jtotal) intensity with respect to solar activity. In principle, the EOF model had an optimal performance at nearly 98&#37; accuracy, with the ANN model exhibiting almost the same degree of accuracy, which appears to be a reference point for ionospheric conditions when looking for space weather applications.

DOI： 10.1029/2021SW002831

Language：Others   Publishing type：Research paper (other academic)  

DOI： 10.1088/1755-1315/880/1/012009

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1093/mnras/stab1161

Language：English   Publishing type：Research paper (scientific journal)  

Identification of fractal properties in geomagnetic data of southeast asian region during various solar activity levels
The fractal properties of geomagnetic northward component data (H-component) in the equatorial region during various phases of solar activity over Southeast Asia were investigated and then quantified using the parameter of the Hurst exponent (H). This study began with the identification of existence of spectral peaks and scaling properties in international quiet day H-component data which were measured during three levels of solar activity: low, intermediate, and high. Then, various cases of quiet and disturbed days during different solar activity levels were analyzed using the method that performed the best in the preceding part. In all the years analyzed, multifractal scaling and spectral peaks exist, signifying that the data have fractal properties and that there are external factors driving the fluctuations of geomagnetic activity other than solar activity. The analysis of various cases of quiet and disturbed days generally showed that quiet days had anti-persistence tendencies (H < 0.5) while disturbed days had persistence tendencies (H > 0.5)—generally a higher level of Hurst exponent compared to quiet days. As for long-term quiet day H-component data, it had a Hurst exponent value that was near H ≃0.50, while the long-term disturbed day H-component data showed higher values than that of the quiet day.

DOI： 10.3390/universe7070248

Language：English   Publishing type：Research paper (scientific journal)  

The Ionosphere at Middle and Low Latitudes Under Geomagnetic Quiet Time of December 2019
The ionospheric electron density shows remarkable day-to-day variability due to solar radiance, geomagnetic activity and lower atmosphere forcing. In this report, we investigated the ionospheric variations at middle and low latitudes during a period under geomagnetic quiet time (Kpmax = 1.7) from November 30 to December 8, 2019. During the quiescent period, the ionosphere is not undisturbed as expected in the Asian-Australian and the American sectors. Total electron content (TEC) has multiple prominent enhancements at middle and low latitudes in the two sectors, and TEC depletions also occur repeatedly in the Asian-Australian sector. The low-latitude electric fields vary significantly, which is likely to be modulated by the notably changing tides in the mesosphere and lower thermosphere region. It is worth noting that the variations of TEC and the electric fields are not consistent in the two sectors, particularly on December 4–6. Further investigation reveals that the increase in TEC depends on altitude. The TEC enhancements are mainly contributed by the altitude below 500 km in both two sectors, which indirectly reflects that the driving sources may come from the lower atmosphere. Especially, a mid-latitude band structure continuously appears at all local times in the North American sector on December 6–8, which is also mainly contributed by the altitude below 500 km.

DOI： 10.1029/2020JA028964

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.asr.2021.01.009

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s12648-020-01734-2

Language：English   Publishing type：Research paper (scientific journal)  

Comparison of eej longitudinal variation from satellite and ground measurements over different solar activity levels
The longitudinal variability and local time of equatorial electrojet (EEJ) current using simultaneous data recorded by ground and satellite magnetometers at different levels of solar activity were investigated. In this study, we used data from the CHAMP and Swarm satellites to obtain EEJ current measurements around the globe. The ground data were provided by the MAGDAS, INTERMAGNET, and IIG networks. The ground observation was carried out by analyzing magnetometer data in four different sectors: the South American, Indian, African, and Southeast Asian sectors. These ground data were normalized to the dip equator to overcome the latitudinal variation of each station. The analysis for both measurements was performed using quiet day data. Both the ground and satellite data were categorized according to solar activity level; low, moderate, and high. The results revealed that, during the low solar activity, there was a good agreement between the longitudinal profiles of the EEJ measured using the satellite and the ground data. In general, strong correlations were obtained in most of the sectors where ground data were available between 11 and 13 local time (LT). Besides that, our analysis revealed that the different times of maximum EEJ appearances were seasonally dependent only at certain longitude sectors.

DOI： 10.3390/universe7020023

Language：Others   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1088/1742-6596/1768/1/012004

Language：Others   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1088/1742-6596/1768/1/012005

Language：English   Publishing type：Research paper (scientific journal)  

Correlations between earthquake properties and characteristics of possible ulf geomagnetic precursor over multiple earthquakes
In this study, we improved and adapted existing signal processing methods on vast geomagnetic field data to investigate the correlations between various earthquake properties and characteristics of possible geomagnetic precursors. The data from 10 magnetometer stations were utilized to detect precursory ultra-low frequency emission and estimate the source direction for 34 earthquakes occurring between the year 2007–2016 in Southeast Asia, East Asia, and South America regions. As a result, possible precursors of 20 earthquakes were identified (58.82&#37; detection rate). Weak correlations were obtained when all precursors were considered. However, statistically significant and strong linear correlations (r ≥ 0.60, p < 0.05) were found when the precursors from two closely located stations in Japan (Onagawa (ONW) and Tohno (TNO)) were exclusively investigated. For these stations, it was found that the lead time of the precursor is strongly (or very strongly) correlated with the earthquake magnitude, the local seismicity index, and the hypocentral depth. In addition, the error percentage of the estimated direction showed a strong correlation with the hypocentral depth. It is concluded that, when the study area is restricted to a specific location, the earthquake properties are more likely to have correlations with several characteristics of the possible precursors.

DOI： 10.3390/universe7010020

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s13369-020-04773-3

Language：English   Publishing type：Research paper (scientific journal)  

Integrating Pre-Earthquake Signatures From Different Precursor Tools.
Potential earthquake precursors include, among others, electromagnetic fields, gas emissions, Land Surface Temperature (LST), Sea Surface Temperature (SST), and Surface Air Temperature (SAT) anomalies. These observables have been individually studied, before earthquakes, by many researchers. The ionospheric studies concerning earthquakes (EQs) using magnetic data from Low Earth Orbit (LEO) satellites are increasingly being used to detect ionospheric anomalies before large EQs. Also, LST, SST, and SAT values retrieved from Moderate Resolution Imaging Spectroradiometer (MODIS) Terra and Aqua satellites and Modern-Era Retrospective analysis for Research and Applications Version 2 (MERRA-2) are considered as physical precursors before EQs. In this work, we jointly analyze magnetic, MODIS, and MERRA-2 data in space and time around the epicenters before the selected EQs in Mexico, Japan, Chile, and Indonesia. Our analyses present interesting findings where anomalies in temperature and magnetic field, preceding the considered EQs, are confirmed through different methods. Particularly, we utilize the Fast Fourier Transform (FFT) and the Discrete Cosine Transform (DCT) for analyzing magnetic data over the designated EQs regions. We use the magnetic data acquired by Swarm satellites in the top side ionosphere along with MODIS and MERRA-2. Five case studies are described to prove the effectiveness of our analyses. Precursory anomalies were observed using these methods in different anomalous days from the considered four regions of interest around the epicenter. It is concluded that these methods could be effective and reliable in detecting anomalies preceding the upcoming EQs.

DOI： 10.1109/ACCESS.2021.3060348

Language：English   Publishing type：Research paper (scientific journal)  

Evolution of field-aligned current in the meridional plane during substorm: multipoint observations from satellites and ground stations
We report the propagation of substorm-associated magnetic fluctuations by multipoint magnetic observations from ground and space in the same meridional plane. The first Quasi-Zenith Satellite (QZS-1), which has a unique orbit of quasi-zenith orbit with an inclination of 41 ∘, an apogee of 7.1 RE radial distance, and an orbital period of 24 h, can stay for a long time in the near-earth magnetotail away from the magnetic equator. We examined a substorm event during 15:00–16:00 UT on July 09, 2013 when QZS-1 was located at 31 ∘ dipole latitude and 23.5 h dipole magnetic local time. The Engineering Test Satellite VIII (ETS-VIII), Time History of Events and Macroscale Interactions during Substorms D (THEMIS-D) at a radial distance of ∼ 10 RE, and THEMIS-E at a radial distance of ∼ 7 RE were located near the equator in the similar magnetic meridian. The dipolarization was first observed at THEMIS-D at 15:14:30 UT. Then, ∼ 1 min later, magnetic fluctuations were observed by ETS-VIII and THEMIS-E. At the same time, the magnetic bay and Pi2 pulsation were observed at low-latitude magnetic observatories and the Radiation Belt Storm Probes B satellite in the inner magnetosphere. We found that QZS-1 away from the equator observed a strong azimuthal magnetic field fluctuation with a long delay of 15 min from the first dipolarization at THEMIS-D near the equator. The speed of the poleward propagating magnetic fluctuation between the ionospheric footprints is calculated to be 310 [m / s] , which is consistent with a typical speed of auroral poleward expansion. A similar time delay of the onset of the negative bay was observed between the Tixie (AACGM MLAT = 66. 8 ∘) and Kotelny (AACGM MLAT = 71. 0 ∘) observatories near the ionospheric footprint of satellites. We suggest that the long delay time of the magnetic fluctuation at QZS-1 was associated with the crossing of field-aligned current during the poleward expansion of the substorm current system. The distribution of azimuthal magnetic field variations in the magnetosphere indicates that the east side downward current extended more west side in the higher latitude part of the current wedge.

DOI： 10.1186/s40623-020-01182-6

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/universe6110200

Language：English   Publishing type：Research paper (scientific journal)  

Prominent Daytime TEC Enhancements Under the Quiescent Condition of January 2017
It is well known that the ionospheric electron densities in the F-region usually undergo day-to-day variability with the magnitude of ~20–35&#37;, associated with the solar as well as geomagnetic activities and the meteorological forcing from the lower atmosphere. In this study, we reported remarkable enhancements in the total electron content (TEC) from the Beidou geostationary (GEO) satellites during the quiescent geophysical condition of January 2017 prior to the arrival of the sudden stratosphere warming (SSW). The daytime TEC around the equatorial ionization anomaly region increased by 75–160&#37; and lasted for several days. The equatorial electrojet and Sq current in the ionospheric E-region at low and middle latitudes showed the corresponding increase during the TEC enhancement interval. The possible contributions from the variations of solar EUV flux and geomagnetic activity are ruled out. Our further analysis showed that the diurnal tides in the temperature from Sounding of the Atmosphere using Broadband Emission Radiometry and the solar and lunar semidiurnal tides of neutral winds from two radars over China became strong during this period of interest. These results suggest that the lower atmospheric tidal forcing could contribute to the great and long-duration TEC enhancement in the ionosphere even though the SSW had not happened yet.

DOI： 10.1029/2020GL088398

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2020JA027939

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/rs12142300

Language：English   Publishing type：Research paper (scientific journal)  

Normalized Polarization Ratio Analysis for ULF Precursor Detection of the 2009 M 7.6 Sumatra and 2015 M 6.8 Honshu Earthquakes
The utilization of geomagnetic field data especially in the ultra-low frequency range has been shown by prior studies to have the potential to detect earthquake precursors. The most widely used signal processing method for this purpose is arguably the polarization ratio analysis. In this paper, the method was improved by introducing a new normalization process with dissimilar ranges for the vertical and horizontal components. The normalized method was applied to geomagnetic field data that were recorded at locations near the earthquakes which had occurred in Sumatra, Indonesia on 30th September 2009 (M7.6) and Honshu, Japan on 12th May 2015 (M6.8) to evaluate the method's reliability and effectiveness in two different regions, i.e., the equatorial and mid-latitudinal regions. The results showed that the precursors obtained from the normalized method were less disturbed by random fluctuations and had more distinguishable amplitudes compared to the non-normalized classic method in both studied regions.

DOI： 10.17576/jkukm-2020-si3(1)-06

Language：English   Publishing type：Research paper (scientific journal)  

<jats:title>Abstract</jats:title><jats:p>In this study, the ionospheric responses in the Asian‐Australian, American, and African sectors during the August 2018 geomagnetic storm were investigated based on the Beidou geostationary orbit (GEO) satellite and Massachusetts Institute of Technology (MIT) Madrigal total electron contents (TECs), combined with measurements from ionosondes, magnetometers, and Global Ultraviolet Imager (GUVI). The middle‐ and low‐latitude TECs were dominated by positive responses over the three longitudinal sectors during the storm on 26–29 August. It is unique that daytime TECs at the Asian‐Australian, American, and African sectors displayed large enhancements larger than 10 TEC units (TECu) on 27–29 August, during the recovery phase, when the ionosphere is usually dominated by plasma depletions due to the ionospheric disturbance dynamo and/or disturbed thermospheric compositions. The combination and competition of the disturbed vertical plasma drifts through the solar wind‐magnetosphere‐ionosphere (SW‐M‐I) coupling and disturbed neutral compositions contribute significantly to the daytime TEC responses at different longitudinal sectors on 26 August during the main and early recovery phases. The eastward equatorial electrojet and O/N<jats:sub>2</jats:sub> during the recovery phase on 27–29 August are larger than the quiet reference, which suggest that the enhanced upward vertical plasma drifts combining with higher O/N<jats:sub>2</jats:sub> make an important contribution on the daytime positive ionospheric storm during the recovery phase. The enhanced vertical plasma drifts could not be driven by the SW‐M‐I coupling or ionospheric disturbance dynamo associated with the geomagnetic storm. Further studies should be untaken to explore the dominant sources for the enhanced upward vertical drifts during the recovery phase.</jats:p>

DOI： 10.1029/2020JA028238

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2020SW002608

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1109/TGRS.2019.2944677

Language：English   Publishing type：Research paper (scientific journal)  

<jats:title>Abstract</jats:title><jats:p>The magnetic field records of the magnetometer networks in the American, East Asian‐Australian, and European‐African sectors were employed in this present work. We used them to investigate equatorial electrojet (EEJ), counter electrojet (CEJ), tidal variability in EEJ strength and ionospheric current during the 2005<jats:bold>/</jats:bold>2006 and 2008<jats:bold>/</jats:bold>2009 sudden stratospheric warming (SSW) events. In addition to the well‐investigated tidal variability in EEJ strength over the American and East Asian sectors, we investigated that of the African sector for the first time. Interestingly, the tidal components in EEJ strength during both SSW events clearly exhibit marked longitudinal differences with high, moderate, and low amplitudes in the American, East Asian, and African sectors, respectively. An exception found around day 71 in the African sector after the 2008<jats:bold>/</jats:bold>2009 SSW event had higher solar diurnal tidal component as compared to that of the Asian sector. Over the American sector, solar and lunar semidiurnal tides were strongly associated with CEJ current during both SSW events, whereas at the African and East Asian sectors such variabilities are not evident. A solar diurnal tidal component was strongly related to a reduction in the EEJ strength over the East Asian sector. In addition, a prolonged period of CEJ occurrence that begins during the SSW precondition and ends when the SSW was evolving characterized the African sector during both SSW events. There is a steady shift in phase at later hours when both SSW events are evolving.</jats:p>

DOI： 10.1029/2019JA026667

Language：English   Publishing type：Research paper (scientific journal)  

<jats:title>Abstract</jats:title><jats:p>The present study shows that the ionospheric Hall polarization can deform the high‐latitude ionospheric convection field, which is widely considered to be a manifestation of the convection field in the magnetosphere. We perform the Hall polarization field separation with a potential solver by changing the conductance distribution step by step from a uniform one to a more realistic one. We adopt dawn‐dusk and north‐south symmetric distributions of conductance and region 1 (R1) field‐aligned current (FAC). The pair of the primary field of the R1 system and each gradient of off‐diagonal component of conductance tensor (Hall conductance) generates the Hall polarization field and consequently causes potential deformations as follows. (a) The equatorward gradient causes clockwise rotation. (b) The gradient across the terminator, together with the effect of the equatorward gradient, causes the dawn‐dusk asymmetry. (c) The high conductance band in the auroral region causes kink‐type deformations. In particular, a nested structure at the equatorward edge of the band in the midnight sector well resembles the Harang Reversal. Result (a) can explain the clockwise bias inexplicable by the IMF‐By effect alone, the combination of (a) and (b) can explain the clearness and unclearness in the round or crescent shapes of the dawn‐dusk cells depending on the IMF‐By polarity, and (c) suggests that the ionosphere may not need the upward‐FAC for the formation of the Harang Reversal. We suggest that the final structure of the ionospheric potential is established by the combined effects of the magnetospheric requirements (external causes) and ionospheric polarization (internal effect).</jats:p>

DOI： 10.1029/2018JA026013

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2019JA027069

Language：English  

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<jats:p>The analysis of 20-year long-term semidiurnal lunar tidal variations gave the evidence that the semidiurnal variations are completely different between the magnetic quiet and disturbed periods. This is the first time that the seasonal dependence of disturbance-time semidiurnal variation has been provided from the analysis of the EE-index. We found the K<jats:sup>p</jats:sup> dependence of semidiurnal variation: For full and new moon phase, counter troughs are amplified during disturbance time, possibly related to disturbance dynamo. For all moon phase, there are positive enhancements in dawn and strong depressions after sunset, resulting from the penetration of polar electric filed. For Seasonal dependence, semidiurnal variations are divided to three seasonal groups, and characterized as deep trough, enhanced crest and weak structure for D-solstice, Equinoxes and J-solstice, respectively. There is no significant longitudinal difference between Ancon and Davao, except for the amplitude of semidiurnal variations. The deep troughs occur during D-solstice and the enhanced crests during Equinoxes, at both Ancon and Davao.</jats:p>

DOI： 10.1051/e3sconf/201912702025

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jastp.2018.01.019

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DOI： 10.1007/s12648-019-01388-9

Language：English   Publishing type：Research paper (scientific journal)  

Assessment of signal processing methods for geomagnetic precursor of the 2012 M6.9 Visayas, Philippines earthquake
Abstract: This study assessed two signal processing methods on geomagnetic data to detect precursory signals appearing before the M6.9 Visayas, Philippines earthquake on 6 February 2012. It aimed to compare the polarization ratio analysis method with the diurnal variation ratio method in terms of reliability and effectiveness. The geomagnetic data were obtained from the MAGDAS magnetometer network for Cebu (CEB) and Legazpi (LGZ) stations which served as the primary and remote stations, respectively. The polarization ratio analysis method was performed on the primary station data to obtain power spectral density in an ultra-low-frequency range before finding the ratio of vertical to total horizontal component. Meanwhile, the diurnal variation ratio method was used to calculate the difference between the daily maximum and minimum values. Then, the ratio of the daily differences of the primary station to the remote station for each individual component was calculated. The disturbance storm time index which describes global geomagnetic activity originating from the Sun was utilized to verify that any observed geomagnetic fluctuations were not caused by solar-terrestrial effect. A precursory anomaly was found using the polarization ratio analysis method which appeared 2 weeks before the earthquake. It is concluded that this method might be effective and reliable in detecting geomagnetic anomalies preceding upcoming earthquakes. In contrast, although the diurnal variation ratio method did show perceivable fluctuations, the running averages were not statistically significant to be considered a precursor. The discrepancy between the analytical results of the two methods may be attributed to the detectability of the earthquake being studied which had a relatively low magnitude. Hence, future studies which utilize more earthquake events need to be conducted to reach a definitive conclusion. Graphic abstract: [Figure not available: see fulltext.].

DOI： 10.1007/s11600-019-00319-w

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jastp.2018.01.012

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DOI： 10.1063/1.5111232

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DOI： 10.1063/1.5111233

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DOI： 10.1007/s12648-018-1318-x

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DOI： 10.1029/2018JA026168

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DOI： 10.1063/1.5111233

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DOI： 10.1063/1.5111232

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DOI： 10.1029/2018EA000537

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DOI： 10.1007/s11200-018-0286-0

Language：English   Publishing type：Research paper (scientific journal)  

<jats:title>Abstract</jats:title><jats:p>We report an extreme erosion of the plasmasphere arising from the September 2017 storm. The cold electron density is identified from the upper limit frequency of upper hybrid resonance waves observed by the Plasma Wave Experiment instrument onboard the Exploration of energization and Radiation in Geospace/Arase satellite. The electron density profiles reveal that the plasmasphere was severely eroded during the recovery phase of the storm and the plasmapause was located at <jats:italic>L</jats:italic> = 1.6–1.7 at 23 UT 8 September 2017. This is the first report of deep erosion of the plasmasphere (<jats:italic>L</jats:italic><jats:sub><jats:italic>PP</jats:italic></jats:sub> < 2) with the in situ observation of the electron density. The degree of the severity is much more than what is expected from the relatively moderate value of the SYM‐H minimum (−146 nT). We attempt to find a possible explanation for the observed severe depletion by using both observational evidence and numerical simulations. Our results suggest that the middle latitude electric field had penetrated from the high‐latitude storm time convection for several hours. Such an unusually long‐lasting penetration event can cause this observed degree of severity.</jats:p>

DOI： 10.1029/2019SW002168

Language：English   Publishing type：Research paper (other academic)  

DOI： 10.1088/1742-6596/1152/1/012022

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DOI： 10.1088/1742-6596/1152/1/012030

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DOI： 10.1088/1742-6596/1152/1/012022

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DOI： 10.1088/1742-6596/1152/1/012035

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DOI： 10.1088/1742-6596/1152/1/012029

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DOI： 10.1088/1742-6596/1152/1/012028

Language：English   Publishing type：Research paper (international conference proceedings)  

The first solar-powered Magdas-9 installation and possible geomagnetically induced currents study at Johor, Malaysia
The Magnetic Data Acquisition System (MAGDAS-9) was successfully installed at Universiti Teknologi MARA Johor, Pasir Gudang Campus, Malaysia (JOH station), under the joint collaboration between International Center for Space Weather Science and Education (ICSWSE), National Space Agency (ANGKASA) and UiTM Johor. This is the first solar-powered magnetometer under the Magnetic Data Acquisition System of Circum-pan Pacific Magnetometer Network (MAGDAS/CPMN). In this paper, construction process, installation process and analysis of first geomagnetic observations at MAGDAS JOH station are presented. In addition, analysis on time derivative of horizontal component of geomagnetic field (dH/dt) to indicate the possibility of Geomagnetically Induced Currents (GIC) occurrences is also presented in this paper. The obtained geomagnetic components: H, D, Z and Total F are approximately similar to World Magnetic Model 2015 (WMM2015) while the diurnal variation from this geomagnetic observation showing a good variation pattern. The analysis of dH/dt has indicated 2 significant events of GIC.

DOI： 10.1088/1742-6596/1152/1/012030

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DOI： 10.1088/1742-6596/1152/1/012035

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DOI： 10.1088/1742-6596/1152/1/012028

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DOI： 10.1029/2018SW002047

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DOI： 10.1029/2019JA026667

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DOI： 10.1109/ICSEngT.2018.8606390

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DOI： 10.1088/1742-6596/1152/1/012029

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DOI： 10.1186/s40623-018-0785-9

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DOI： 10.1186/s40623-018-0785-9

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DOI： 10.1029/2017JA024375

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DOI： 10.1029/2018JA025601

Language：Others   Publishing type：Research paper (scientific journal)  

Changes in ionospheric currents system at southeast Asia region during geomagnetic storm in solar's minimum phase
Equatorial ionospheric current system consists of equatorial electrojet (EEJ) and solar quiet (Sq). EEJ current is a ribbon of current flowing eastwards along the dip equator region. On the other hand, Sq current is a loop of current that flows at the Earth's northern and southern hemispheres in different directions. This study is focusing on analysing the effects of a solar event on the latitudinal profile of the current system, specifically in Southeast Asian region. Data used in this study are geomagnetic data from five magnetometer stations in MAGDAS network which are Muntinlupa (MUT), Cebu (CEB), Davao (DAV), Manado (MND) and Pare Pare (PRP). The EEJ current intensity is known to be highest around noon time between 1000 and 1100 LT during solar minimum and thus this study analyses the current system from 1000 to 1400 LT. The analysis showed that the geomagnetic storm occurred on 23 April 2008, which is caused by coronal mass ejection (CME), gives rises to the currents on that day. This increment is clearly observed on the currents at the southern hemisphere stations, which are MND and PRP. Our analysis also found that this geomagnetic storm gives increment to the current at the non-peak time. Apart from that, the current profile on this day is compared with the current profile from a quiet day on 21 April 2008.

DOI： 10.17576/jsm-2018-4708-34

Language：English   Publishing type：Research paper (scientific journal)  

<jats:title>Abstracts</jats:title><jats:p>During 26–29 March 2017 magnetic storm, the Arase satellite observed typical ultra low frequency (ULF) waves and acceleration of relativistic electrons. We simulate the global distribution of these ULF waves using CRCM with BATSRUS global magnetospheric magnetohydrodynamic model. The simulation can qualitatively reproduce the ULF waves observed by Arase at frequencies of 2–3 mHz. However, the simulated ULF wave power is 1–2 orders of magnitude smaller than the observation. The simulated ULF wave activity has a good correlation with the solar‐wind dynamic pressure variation, while the wave activity on the ground is enhanced even during the recovery phase, possibly due to the Kelvin‐Helmholtz instability and/or substorms. We also study the 3–6 April 2017 magnetic storm, in which low ULF wave activity and weak acceleration of relativistic electrons are seen. We suggest that the existence of ULF waves plays an important role in accelerating electrons up to relativistic energies.</jats:p>

DOI： 10.1029/2018GL078857

Language：English   Publishing type：Research paper (scientific journal)  

<jats:title>Abstract</jats:title><jats:p>Results from a new drift kinetic model in the topside ionosphere capture the mode conversion from kinetic Alfven waves to electron acoustic waves. When the kinetic Alfven waves propagate into the transition region, where the electron density of ionospheric origin becomes comparable to that of magnetospheric origin, the steep temperature gradient leads to the mode conversion. The electron acoustic waves are short‐lived by dissipating their energy into the electron energization, thus revealing a new type of electron acceleration in the topside ionosphere.</jats:p>

DOI： 10.1029/2018GL077898

Language：English  

Study of the Solar Wind Influence on the Jovian Inner Magnetosphere Using an Ionospheric Potential Solver

Language：English  

Anomalous ultra low frequency signals possibly linked with seismic activities in Sumatra, Indonesia

Language：English  

DOI： 10.1002/9781119324522.ch25

Language：English  

The Time Derivative of the Horizontal Geomagnetic Field for the Low Latitude MAGDAS Langkawi Station for the Estimation of Geomagnetically Induced Current

DOI： 10.1007/978-981-10-6574-3_6

Language：English   Publishing type：Research paper (other academic)  

DOI： 10.1109/ICSEngT.2018.8606390

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.17576/jsm-2018-4703-21

Language：English   Publishing type：Research paper (scientific journal)  

DOI： DOI10.4283/ JMAG.2017.22.2.333.

Language：English   Publishing type：Research paper (scientific journal)  

Nighttime Pc3 pulsations: MM100 and MAGDAS observations
In this paper, we present a statistical and case analysis of nighttime Pc3 pulsations observed from middle to equatorial latitudes during the year 2003. We found two groups of nighttime Pc3 pulsations. Pc3s of the first group are in fact the nightside counterpart of morning Pc3 pulsations with large azimuthal scales slowly attenuating toward midnight. Such night signatures of morning Pc3 waves are observed during the periods of fast solar wind (V > 500 km/s). The second type is the locally generated night Pc3 pulsations. They can be observed under moderate solar wind velocities. Maximal occurrence rates and amplitudes for these pulsations are recorded at middle geomagnetic latitudes near the local magnetic midnight. Probably, they are associated with auroral activations or local non-substorm bursty processes.

DOI： 10.1186/s40623-017-0647-x

Language：English   Publishing type：Research paper (other academic)  

Characteristics of Schumann Resonance Parameters at Kuju Station
The ground magnetic field variation in the extremely low frequency (ELF) range has been measured by an induction magnetometer at Kuju, Japan (KUJ; M.Lat. = 23.4 degrees, M. Lon. = 201.0 degrees) since 2003. The first mode of the Schumann resonance (SR) around 8 Hz can be seen at KUJ. The SR in H (horizontal northward component) shows maximum peaks around 08 UT and 15 UT. In the case of D (horizontal eastward component), the SR shows its maximum peak around 08 UT. These peaks are coincident with the enhancement of lightning activity in Africa and Asia. Thus, we found the influence of the lightning activity on the observed SR at KUJ.

DOI： 10.1051/e3sconf/20172001004

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/2017SW001613

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.asr.2017.02.003

Language：English   Publishing type：Research paper (other academic)  

DOI： 10.1088/1742-6596/852/1/012019

Language：English   Publishing type：Research paper (other academic)  

DOI： 10.1088/1742-6596/852/1/012015

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/2016JA023754

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Longitudinal variation of equatorial electrojet and the occurrence of its counter electrojet
We examined the longitudinal variability of the equatorial electrojet (EEJ) and the occurrence of its counter electrojet (CEJ) using the available records of the horizontal component H of the geomagnetic field simultaneously recorded in the year 2009 (mean annual sunspot number Rz Combining double low line 3.1) along the magnetic equator in the South American, African, and Philippine sectors. Our results indicate that the EEJ undergoes variability from one longitudinal representative station to another, with the strongest EEJ of about 192.5nT at the South American axis at Huancayo and a minimum peak of 40.7nT at Ilorin in western Africa. Obtained longitudinal inequality in the EEJ was explicable in terms of the effects of local winds, dynamics of migratory tides, propagating diurnal tide, and meridional winds. The African stations of Ilorin and Addis Ababa registered the greatest &#37; of CEJ occurrence. Huancayo in South America, with the strongest electrojet strength, was found to have the least occurrence of the CEJ. It is suggested that activities that support strong EEJ inhibits the occurrence of the CEJ. Percentage of occurrence of the CEJ varied with seasons across the longitudes. The order of seasonal variation of morning occurrence does not tally with the evening occurrence order at any station. A semiannual equinoctial maximum in percentage of morning occurrence of the CEJ was obtained at Huancayo and Addis Ababa. Only Addis Ababa recorded equal equinoctial maxima in percentage of evening occurrence of the CEJ. The seasonal distribution of the occurrences of the CEJ at different time regimes implies a seasonal variability of causative mechanisms responsible for the occurrence of the CEJ.

DOI： 10.5194/angeo-35-535-2017

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s11430-016-0096-y

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.5194/angeo-35-535-2017

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s11430-016-0096-y

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/2016JA023370

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/2016JA023370

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.5013/IJSSST.a.17.41.30

Language：English   Publishing type：Research paper (scientific journal)  

Longitudinal profile of the equatorial electrojet current and its dependence on solar activity
The equatorial electrojet (EEJ) is a strong eastward ionosphere current flowing in a narrow band along dip equator. It is flowing eastward in the dayside of equatorial E region of about 600 km wide and within 90 to 130 km altitude. The objectives of this research is to study the variations Equatorial Electrojet (EEJ) current measured from ground_based magnetometer. The data were provided by magnetometer network such as Magnetic Data Acquisition System (MAGDAS)/Circum-pan Pacific Magnetometer Network (CPMN), Indian Institute of Geomagnetism (IIG), International Real-time Magnetic Observatory Network (INTERMAGNET). We also request the data from the single observation station such as Fuquene (FUQ). The analysis is carried out using the EUEL index and normalization technique is applied to yield better results with the aids of CM4 current model. This involves fourteen stations in South America, African, Indian and Southeast Asian sectors. The analysis done are including longitudinal and solar activity dependence where the years revolves are 2008 and 2011. These two years represents the minimum phases of solar activity (2008) and inclining phases of solar activity (2011). The results obtained show that EEJ varies with longitudes and solar activity. EEJ current is found to be highest at the American sector and lowest between African and Indian sector. This current is also highest in inclination phase during 2011 compared to 2008 (solar minimum).

DOI： 10.1166/asl.2017.8372

Language：English   Publishing type：Research paper (scientific journal)  

Latitudinal variation of ionospheric currents in Southeast Asian sector
The equatorial electrojet (EEJ) is a current system caused by the enhanced ionospheric conductivity near the dayside magnetic dip equator. In this study, we attempt to obtain the latitudinal profile of Sq and total current component (EEJ+Sq) and consequently attain the EEJ latitudinal variation. Analysis is carried on using magnetic data recorded at six stations in Southeast Asian sector. The data used are equatorial electrojet index, EUEL, which were calculated from geomagnetic northward, H, component on geomagnetically quiet days. We further compared latitudinal profile of Sq and total current during solar minimum (2008) and solar maximum (2014) in order to study their solar cycle dependence. Furthermore, we examined the EEJ circuit for both solar activity period. Result shows that as the EEJ strength increase with solar activity, it contribute to higher increase in total current during 2014, and consequently contribute to significant difference in the total current latitudinal profile during 2008 and 2014. On the other hand, the EEJ latitudinal variation illustrates the current circuit where the reverse current was observed to start on the flanks of dip equator at about 5° and terminate at less than 10° latitude in both hemispheres.

DOI： 10.1166/asl.2017.8358

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1017/S1743921318000662

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40623-016-0517-y

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DOI： 10.1186/s40623-016-0514-1

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DOI： 10.1002/2016JA023143

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DOI： 10.1002/2016JA022958

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DOI： 10.1002/2016JA022857

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DOI： 10.1002/2015JA021698

Language：English  

DOI： 10.1186/s40623-015-0350-8

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/2015JA021698

Language：English   Publishing type：Research paper (scientific journal)  

©2016. American Geophysical Union. All Rights Reserved. A detailed investigation is carried out to understand the prolonged (∼44 h) weakly southward interplanetary magnetic field (IMF-Bz) condition during 2–4 May 1998. In situ observations, during the period, show the passage of an expanding magnetic cloud embedded in an interplanetary coronal mass ejection (ICME), followed up by a shock and an interplanetary discontinuity driven by another ICME. It is the arrival of the ICMEs and the upfront shocks that caused the prolonged southward IMF-Bz condition. The magnetic configuration of the source regions of the IMF associated with the ICME interval was also examined, which showed open magnetic field structures, emanating from a small active region on the north of the heliospheric current sheet (HCS). The structures remained constantly to the north of the HCS, both on 29 April and 1 May, suggesting no change in their polarity. The draping of these outward directed radial field lines around the propagating CMEs in the shocked plasma explains the observed polarity changes of the IMF-Bz at 1 AU. In addition, multiple enhancements were also detected in the geomagnetic field variations, which showed a distinct one-to-one correspondence with the density pulses observed at 1 AU, during 0700–1700 UT on 3 May. The spectral analyses of both the variations showed the same discrete frequencies of 0.48, 0.65, and 0.75 mHz, demonstrating that the solar wind density enhancements can cause detectable global geomagnetic disturbances. The observations, thus, provide a deeper insight into the possible causes and geomagnetic consequences of a prolonged weakly southward IMF-Bz condition.

DOI： 10.1002/2015JA022185

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/2015JA022185

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40623-015-0350-8

Language：English   Publishing type：Research paper (scientific journal)  

The characteristics of the F2 layer parameters NmF2 and hmF2 over Dibrugarh (27.5° N, 95° E, 17° N geomagnetic, 43° dip) measured by a Canadian Advanced Digital Ionosonde (CADI) for the period of August 2010 to July 2014 are reported for the first time from this low mid-latitude station lying within the daytime peak of the longitudinal wave number 4 structure of equatorial anomaly (EIA) around the northern edge of anomaly crest. Equinoctial asymmetry is clearly observed at all solar activity levels whereas the midday winter anomaly is observed only during high solar activity years and disappears during the temporary dip in solar activity in 2013 but forenoon winter anomaly can be observed even at moderate solar activity. The NmF2/hmF2 variations over Dibrugarh are compared with that of Okinawa (26.5° N, 127° E, 17° N geomagnetic), and the eastward propagation speed of the wave number 4 longitudinal structure from 95° E to 127° E is estimated. The speed is found to be close to the theoretical speed of the wave number 4 (WN4) structure. The correlation of daily NmF2 over Dibrugarh and Okinawa with solar activity exhibits diurnal and seasonal variations. The highest correlation in daytime is observed during the forenoon hours in equinox. The correlation of daily NmF2 (linear or non-linear) with solar activity exhibits diurnal variation. A tendency for amplification with solar activity is observed in the forenoon and late evening period of March equinox and the postsunset period of December solstice. NmF2 saturation effect is observed only in the midday period of equinox. Non-linear variation of neutral composition at higher altitudes and variation of recombination rates with solar activity via temperature dependence may be related to the non-linear trend. The noon time maximum NmF2 over Dibrugarh exhibits better correlation with equatorial electrojet (EEJ) than with solar activity and, therefore, new low-latitude NmF2 index is proposed taking both solar activity and EEJ strength into account.

DOI： 10.1186/s40623-015-0355-3

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40623-015-0373-1

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s12517-015-1858-8

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (other academic)  

DOI： 10.1109/IconSpace.2015.7283762

Language：English   Publishing type：Research paper (other academic)  

DOI： 10.1109/IconSpace.2015.7283763

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Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1134/S001095251504005X

Language：English   Publishing type：Research paper (scientific journal)  

©2015. American Geophysical Union. All Rights Reserved. We have used chains of Magnetic Data Acquisition System (MAGDAS) magnetometer records of the horizontal (H) and vertical (Z) magnetic field intensities during September 2008 to August 2009 (year of deep minimum) across Africa to study their variability during the quietest international days, which coincidently associated with the sudden stratospheric warming (SSW) event in January 2009. This selection of the most international quiet days is indicative of 80&#37; that are strongly associated with days when unusually strong and prolonged sudden SSW event occurs in January 2009. Interestingly, in January, a significant magnitude depletion of solar quiet (Sq) equivalent current was observed near noon hours around the magnetic equator (Addis Ababa, ABB) compared to any other months along with a consistent significantly reduced value across the Northern Hemisphere and moderate decrease at the Southern Hemisphere. Also, we found that Nairobi and Dar es Salaam at the Southern Hemisphere, which are close to ABB (dip equator), are strongly prone to westward electric field compared to the magnetic equator and Khartoum at the Northern Hemisphere. Significant negative values of MSq(Z) magnitudes observed near noon hours at Hermanus indicate the presence of induced currents that suggest ocean effects along with reversal to significant positive values in the afternoon, which subsided before 1800-LT in almost all the months, indicate stronger influence of ionospheric currents. On seasonal variability of Sq(H), a slight depression at ABB during September equinox is one of the evidences of seasonal Sqfocus shift. Latitudinal variability of Sqnear-noon hours was also investigated. Key Points Abnormal intensification of electric currents Latitudinal sections of the African stations Highest and positive magnitude in February

DOI： 10.1002/2014JA020728

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/2014JA020728

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DOI： 10.1002/2013JA019691

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/2013JA019691

Language：English   Publishing type：Research paper (scientific journal)  

CDF data archive and integrated data analysis platform for ERG-related ground data developed by ERG Science Center (ERG-SC)
The Exploration of energization and Radiation in Geospace project Science Center (ERG-SC) has developed the science data file archive and integrated data analysis tool for the ground network observation data of the ERG project. We have organized data design consortiums to develop and elaborate the standard metadata and data variable sets for each type of the ERG-related ground data being archived as Common Data Format (CDF) files. The integrated data analysis software for the project has also been developed on the basis of the Space Physics Environment Data Analysis Software (SPEDAS) which works in concert with the CDF data file repository. The software tools, which are provided as plug-in libraries for SPEDAS, are made available to the international science community so that scientists and students are ready to proceed to integrated studies combining the ground data with other satellite and simulation data seamlessly. The integrated data analysis software can make scientific activities more productive and help the ERG project achieve the scientific goals.

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.asr.2014.11.010

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.asr.2014.11.010

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DOI： 10.5614/j.math.fund.sci.2015.47.1.7

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DOI： 10.1002/2014JA020665

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DOI： 10.1002/2014JA020526

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DOI： 10.1186/s40623-014-0146-2

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DOI： 10.1002/2014SW001110

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DOI： 10.1016/j.nrjag.2014.09.001

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DOI： 10.1002/2014JA020273

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DOI： 10.1002/2014JA020273

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DOI： 10.1002/2012JA018585

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DOI： 10.1002/2012JA018585

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DOI： 10.1186/1880-5981-66-20

Language：English   Publishing type：Research paper (scientific journal)  

<jats:p>Quiet time daily variations of the geomagnetic field near the magnetic equator due to the equatorial electrojet are simulated using the National Center for Atmospheric Research Thermosphere‐Ionosphere Electrodynamics General Circulation Model (TIE‐GCM) and compared to those observed by ground‐based magnetometers. Simulations are run both with and without tidal forcing at the height of the model lower boundary (∼97km). When the lower boundary forcing is off, the wind that generates an electromotive force in the model is primarily the vertically nonpropagating diurnal tide, which is excited in the thermosphere due to daytime solar ultraviolet heating. The lower boundary tidal forcing adds the effect of upward propagating tides, which are excited in the lower atmosphere and propagate vertically to the thermosphere. The main objective of this study is to evaluate the relative importance of these thermospherically generated tides and upward propagating tides in the generation of the equatorial electrojet. Fairly good agreement is obtained between model and observations when the model is forced by realistic lower boundary tides based on temperature and wind measurements from the Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics (TIMED) satellite, as determined by Wu et al. (2012). The simulation results show that the effect of upward propagating tides increases the range of the geomagnetic daily variation in the magnetic‐northward component at the magnetic equator approximately by 100&#37;. It is also shown that the well‐known semiannual change in the daily variation is mostly due to upward propagating tides, especially the migrating semidiurnal tide. These results indicate that upward propagating tides play a substantial role in producing the equatorial electrojet and its seasonal variability.</jats:p>

DOI： 10.1002/2013JA019487

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DOI： 10.14716/ijtech.v5i3.612

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DOI： 10.1016/j.srt.2013.11.007.

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DOI： 10.1002/jgra.50513

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DOI： 10.1002/jgra.50514

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DOI： 10.1109/IconSpace.2013.6599453

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DOI： 10.1002/jgra.50355

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DOI： 10.1002/jgra.50355

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DOI： 10.1002/jgra.50318

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DOI： 10.1002/jgra.50254

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DOI： 10.1029/169GM19

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DOI： 10.1029/2012JA017899

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DOI： 10.1029/2012JA017899

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DOI： 10.5194/angeo-29-1663-2011

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DOI： 10.1029/2011JA016487

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DOI： 10.1029/2011JA016460

Language：Japanese   Publishing type：Research paper (scientific journal)  

一般に，前兆現象は突発現象にそのものに比べて非常に目立ちにくく，その開始時刻は曖昧である．従来よく用いられてきた変化点検出法を適用した場合，このような微小で緩慢な変化は見逃されやすい．Tokunagaら(2010)では，Ideら(2005)の提案した特異スペクトル分析を応用した変化点検出法（SST）を，多次元データを用いたアルゴリズム（MSST）へと拡張することで，鋭敏に前兆現象の開始時刻を推定できることを示した．MSSTは，緩慢な変化も検出できる鋭敏な手法であるが，実データへの適用では誤検出が問題になる．本稿では，突発現象の大まかな開始時刻をあらかじめ検出し，さらに検出された時刻の前後で前兆現象の開始時刻と終了時刻を個別に探索することで，前兆現象を鋭敏に検出でき，かつMSST単体よりも誤検出を劇的に減少させることができることを示す．In general, precursory events are observed as minute and less-visible fluctuations preceding an onset of massive fluctuations of extraordinary phenomena. Hence, existing change-point detection methods most likely overlook precursory events. Tokunaga, et al. (2010) extended the method for detecting the change-points, Singular Spectrum Transformation (SST) proposed by Ide, et al. (2005), to the multivariable SST (MSST). Although MSST can detect minute changes, we have to reduce false positives because real world data includes non-stationary trends and measurement noise. In this paper, we propose the algorithm to detect precursory events in an off-line manner. Our algorithm consists of three kinds of change-point detection methods. We show that the number of false positive reduce drastically by combining three different types of change-point detection methods.

Language：English   Publishing type：Research paper (scientific journal)  

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DOI： 10.1029/2010JA016042

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DOI： 10.1029/2010JA016042

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Language：Others  

DOI： 10.1007/s10120-010-0559-y, 10.1016/j.ejca.2016.04.012_references_DOI_UX2wletTCS6Zbzczafu5vBKIFKF, 10.1634/theoncologist.2019-0601_references_DOI_UX2wletTCS6Zbzczafu5vBKIFKF, 10.3892/ol.2011.525_references_DOI_UX2wletTCS6Zbzczafu5vBKIFKF, 10.1200/jco.18.01

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2009JA014397

Language：English   Publishing type：Research paper (scientific journal)  

<jats:p>This study proposes a new formula that describes a dynamical magnetosphere‐ionosphere (MI) coupling system through the field‐aligned current (FAC) closure and electrostatic potential connectivity. In the past, MI coupling processes were described as either “inductive” or “static.” The inductive coupling scheme is based on the reflection of MHD waves at the ionosphere, whereas in the static coupling scheme the electrostatic potential is determined through the FAC closure. In contrast, in our new formulation these two schemes are combined by the “Alfvenic‐coupling” algorithm. The concept of the Alfvenic coupling is as follows. When a distribution of ionospheric current is changed from the background condition through the mapping of magnetospheric disturbances and/or by the change of ionospheric conductivity, an ionospheric reflection electric filed is instantaneously generated to satisfy the current continuity condition. The electrostatic potential of this reflection field also feeds back to the magnetosphere and excites shear Alfvenic disturbances in the magnetosphere. Therefore, the current continuity condition has to include the FAC of Alfvenic disturbances. In this sense, the reflection potential is not only a modification of the ionospheric potential but also a source of inductive Alfvenic disturbances. Quantitative estimation of feedback components to the magnetosphere reveals that our new formulation is more suitable to global MI simulations than the static MI coupling, which has been the only scheme used in the past.</jats:p>

DOI： 10.1029/2009JA014924

Language：English   Publishing type：Research paper (scientific journal)  

<jats:p>We examined the correlation between nighttime Pi2 pulsations detected simultaneously by a frequency modulated continuous wave (FM‐CW) (HF) radar and by a ground magnetometer, both located at a midlatitude (L = 2.05) Magnetic Data Acquisition System station. Eighty‐three Pi2 events were observed during the 43 day period from 23 September 2006 to 4 November 2006. The variations of the ground magnetic <jats:italic>H</jats:italic> component and ionospheric Doppler velocity (<jats:italic>V</jats:italic>*) exhibited high coherence for 80&#37; of the 83 Pi2 events, for about a half of which the H and <jats:italic>V</jats:italic>* variations have the same dominant frequency. For such events, <jats:italic>V</jats:italic>* led <jats:italic>H</jats:italic> by 90° in phase, in the midnight sector of 2230–0300 LT. The average <jats:italic>Ey</jats:italic> (east‐west electric field) amplitude derived from <jats:italic>V</jats:italic>* is 0.27 mV/m. The 90° phase delay was not found for the five events that were observed near dusk and dawn. The phase relation of <jats:italic>H</jats:italic> and <jats:italic>V</jats:italic>* for Pi2s in the midnight sector may be explained in terms of the radial standing structure of compressional waves, i.e., cavity mode oscillation.</jats:p>

DOI： 10.1029/2009JA014397

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DOI： 10.1142/9789812838209_0027

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.pss.2008.05.019

Language：English   Publishing type：Research paper (scientific journal)  

We analyzed ground magnetometer data for the 10 International Quiet Days during 1996-2007. The data were obtained from 19 stations along 210°magnetic meridian (MM) of the Circum-pan Pacific Magnetometer Network (CPMN) covering both the Northern Hemisphere and Southern Hemisphere. From the daily variations of the geomagnetic field, we deduced the latitude-local time (LAT-LT) diagram of the equivalent Sq current system, which can be regarded as the superposition of the following three current systems: Sqo, Sq 1, and Sq2. The Sq0, Sq1, and Sq2 current systems are equivalent current systems for the yearly average, annual variation, and semiannual variation of the Sq field, respectively. We have examined temporal and spatial features of these current systems. The principal features are as follows: (1) The total current intensities of the Sq1 and Sq2 current systems are about 35&#37; and 15&#37; of that of the Sq0 current system, respectively. (2) The Sq0 and Sq2 current systems have a dayside vortex in each hemisphere, while the Sq1 current system has a single vortex centered at the equatorial region in the morning sector (∼1000 LT). Copyright 2009 by the American Geophysical Union.

DOI： 10.1029/2009JA014638

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2009JA014638

Language：English   Publishing type：Research paper (scientific journal)  

We analyzed ground magnetometer data for the 10 International Quiet Days during 1996-2007. The data were obtained from 19 stations along 210°magnetic meridian (MM) of the Circum-pan Pacific Magnetometer Network (CPMN) covering both the Northern Hemisphere and Southern Hemisphere. From the daily variations of the geomagnetic field, we deduced the latitude-local time (LAT-LT) diagram of the equivalent Sq current system, which can be regarded as the superposition of the following three current systems: Sqo, Sq 1, and Sq2. The Sq0, Sq1, and Sq2 current systems are equivalent current systems for the yearly average, annual variation, and semiannual variation of the Sq field, respectively. We have examined temporal and spatial features of these current systems. The principal features are as follows: (1) The total current intensities of the Sq1 and Sq2 current systems are about 35&#37; and 15&#37; of that of the Sq0 current system, respectively. (2) The Sq0 and Sq2 current systems have a dayside vortex in each hemisphere, while the Sq1 current system has a single vortex centered at the equatorial region in the morning sector (∼1000 LT). Copyright 2009 by the American Geophysical Union.

DOI： 10.1029/2009JA014638

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2009JA014163

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2009JA014163

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2009JA014124

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2009JA014124

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2009JA014124

Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.5194/angeo-26-3913-2008

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2007JA012585

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2007JA012585

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2007JA012585

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.pss.2006.03.016

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.asr.2005.05.089

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/BF03351959

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2003JA010242

Language：English   Publishing type：Research paper (scientific journal)  

<jats:p>During a magnetic storm of 18 April 2002, quasi‐periodic variations of the low‐energy electron flux were observed by the LANL satellites at geosynchronous orbit; this phenomenon has been called the “sawtooth event.” During this event, on the ground, magnetic bays and Pi 2 pulsations took place corresponding to each enhancement of the particle flux, and they had features typical to usual substorms. However, unlike typical substorms, the ACE satellite observed no apparent northward turnings of the IMF corresponding to the sawtooth event. In this study, we used ground magnetic data from middle‐ and low‐latitude stations which are distributed widely in the longitudinal direction, selected from the CPMN (Circum‐Pan Pacific Magnetometer Network) and INTERMAGNET stations and compared the magnetic variations during the sawtooth event with that of the typical substorm (Lester et al., 1984). We found that the local time distribution of the polarization axis of the Pi 2 pulsations show a good agreement with that for a typical substorm, except that the local time width of the expected current wedge was 12 hours. On the other hand, the <jats:italic>H</jats:italic> component is predominant in the amplitude of the magnetic bay on the ground; the distribution of the <jats:italic>H</jats:italic> component also suggests a 12‐hour‐wide current wedge, which did not develop much in time. From these features, it is suggested that a current wedge was formed during this sawtooth event, and it generated the Pi 2 pulsations on the ground. However, the local time width of the current wedges is much wider than typical substorms, and its uniqueness causes the ground features different from typical substorm‐associated magnetic variations on the ground.</jats:p>

DOI： 10.1029/2004JA010734

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2004JA010734

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2003JA009898

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2003JA009898

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2003JA009903

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2003JA009903

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

<jats:p>To clarify the process by which an ionospheric current system is formed by field‐aligned current (FAC) closure in the ionosphere, an inclusive formulation of magnetosphere–ionosphere (MI) coupling is undertaken. The “Hall‐current generator”, which is excited during the transient phase of MI coupling, plays a crucial role in the formation of the ionospheric rotational‐current system. It extracts energy from the FAC system through the divergent Hall‐current and pumps it into the rotational Hall‐current. The energy of the rotational current accumulates as an evanescent poloidal magnetic field, associated with the ionospheric surface wave. This accumulated energy is also fed back to the FAC system through the change in energy flow of the Hall‐current generator. It is found that there is a typical timescale for the rotational‐current system to accumulate or extract the poloidal magnetic energy of ionospheric surface waves. This depends on the inductance of the rotational‐current system and the effective conductivity of the ionospheric rotational current. This characteristic timescale becomes the cause of an ionospheric inductive effect, such as a time delay or phase lag between the source electromagnetic field of the FAC and the corresponding poloidal magnetic field on the ground. The latter causes an inductive shielding effect on the amplitude of the geomagnetic disturbance. Numerical simulation has been able to explain the details of the physical process that occurs when the incident FAC is developing and decaying, and how the energy and current are redistributed into the other elements during the transient MI‐coupling process.</jats:p>

DOI： 10.1029/2001JA009170

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2001JA009170

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2000JA000405

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2000JA000405

Language：English   Publishing type：Research paper (scientific journal)  

<jats:p>A new formula describing the inductive response of the magnetosphere‐ionosphere‐atmosphere‐Earth electromagnetic coupled system to the time development of the field‐aligned current (FAC) source‐field is developed. Using this new formula, the Hall‐induced inductive shielding effect (ISE) on geomagnetic pulsation is investigated. The ISE is caused by the reduction of the amplitude of total rotational current because of the generation of “inductive” rotational current by the inductive part of ionospheric divergent electric field, which originates the existence of divergent Hall current. It will be shown that the ISE is more efficient for high‐frequency pulsations, large horizontal scale phenomena and high‐conducting ionospheric conditions. Quantitative analysis strongly suggests that the ionospheric conductivity in the dayside hemisphere can easily reach and sometimes exceed the turning point of geomagnetic pulsations of which frequencies are in the Pc 3 ∼ 4 pulsations range.</jats:p>

DOI： 10.1029/2001GL013610

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

<jats:p>It has been well recognized that field‐aligned current (FAC) systems lose their energy in the ionosphere through the Joule dissipation that is caused by their closure via the ionospheric Pedersen current, and that the ionospheric Hall current cannot contribute the total energy dissipation. However, it is also true that the rotational Hall current is excited by the incident FAC, and it radiates a Poynting vector that grows a poloidal‐type magnetic field. Even if the Hall effect cannot do work on an external system, what does its contribution to the accumulation of poloidal magnetic energy really mean? In this paper, it is clarified that the divergent Hall current, excited during the transient phase of magnetosphere‐ionosphere coupling, closes via the FAC and produces a Hall current generator, which pumps up the energy of the FAC system to increase the ionospheric rotational Hall current (together with its associated poloidal magnetic field).</jats:p>

DOI： 10.1029/2001GL014125

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2001JA900137

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2001JA900137

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2000GL000108

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/BF03351654

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/1999GL010767

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/1999ja000159

Language：English   Publishing type：Research paper (scientific journal)  

Language：English  

Ground magnetic perturbations associated with the standing toroidal mode oscillations in the magnetosphere-ionosphere system
The behavior of toroidal mode oscillations of standing Alfvén waves (refer to as standing Alfvén oscillations) in the coupled magnetosphere-ionosphere system is investigated using a trapezoid-shape magnetosphere model. It is found that the magnetic perturbation is transmitted across the ionosphere differently in the two cases where the ionospheric electric field perturbation is static (Pedersen conductivity > Hall conductivity) and where it is inductive (Pedersen conductivity < Hall conductivity). It is noted that the ionospheric Hall current for the inductive condition shields the magnetic field perturbation. The north-south asymmetry of the conjugate ground magnetic perturbations is calculated by using a trapezoid model with the ionospheric and magnetospheric parameters based on the IGRF and IRI. It is revealed that the ionospheric electric field is almost static for the fundamental mode oscillation, whereas inductive for the higher harmonic ones. It is also found that the north-south asymmetry of the ground magnetic perturbations depends not only on the L-value but also on magnetic longitude; this is because the ionosphere and magnetic field conditions are not uniform as a function of longitude.

DOI： 10.1186/BF03351669

Language：English   Publishing type：Research paper (scientific journal)  

<jats:p>In order to understand the effect of ionosphere on the localized toroidal magnetic shell oscillation (field line oscillation), we have constructed a rectangular box model for the magnetosphere‐ionosphere‐solid earth system including the anisotropically conducting ionosphere and performed the eigenmode analysis of the magnetohydrodynamic (MHD) waves in the model. We have found that the eigenmodes of field line oscillation are effectively controlled by the height‐integrated Pedersen and Hall conductivities, meaning that the field‐aligned current (FAC) in the magnetosphere is closed to both the Pedersen current and the Hall current. The divergent Hall current, that is, the Hall current, which closes the FAC, is a newfound current that is driven by the Hall effect of the ionospheric inductive (rotational) electric field. The divergent Hall current brings into sharp relief by considering the ionosphere to be inductive, and it inevitably requires the electromagnetic coupling between the magnetosphere, ionosphere, atmosphere, and solid earth. The nature of the ionospheric current associated with the standing shear Alfvén mode is also analyzed in detail by using the concept of wave reflection and mode conversion at the inductive ionosphere. In particular, we emphasize that the magnetic flux sustained by the rotational Hall current, that is, accompanied by the radiation of fast magnetosonic wave to the magnetosphere and atmospheric poloidal magnetic wave to the atmosphere, should be taken into account for magnetosphere‐ionosphere coupling of FAC.</jats:p>

DOI： 10.1029/1999ja900287, 10.1186/bf03351669_references_DOI_QZjTXhdUbFP8cCtoeB591eezRJP, 10.1029/2011ja016460_references_DOI_QZjTXhdUbFP8cCtoeB591eezRJP, 10.1186/bf03351736_references_DOI_QZjTXhdUbFP8cCtoeB591eezRJP, 10.1186/bf03352541_references_DOI_QZjTXhdU

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/S1364-6826(97)00110-7

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/97GL02146

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

A general expression for the reflection and mode conversion of MHD waves at the ionosphere is derived. On the basis of the expression, the effect of ionospheric divergent Hall current (Hall part of the induction current associated with the inductive electric field of fast magnetosonic wave) on localized toroidal oscillation is examined. When the horizontal scale of localized oscillation is of the order of several times of the height of ionosphere, the inductive electric field can play a significant role in the reflection of shear Alfvén waves with longer periods (e.f., - 100 s) in the high-latitude region, especially, in the auroral zone. Then, the contribution of the divergent Hall current to the field-aligned one can be no longer neglected and so the eigenfrequency of localized toroidal oscillation is effectively controlled by the height-integrated Hall conductivity in the ionosphere.

DOI： 10.1029/95GL03580

Language：English   Publishing type：Research paper (scientific journal)  

Event date： 2023.12

Language：English   Presentation type：Oral presentation (general)  

Venue：San Francisco   Country：United States  

プラズマのマルチスケール結合が本質となるオーロラ物理学について、量子アルゴリズムの適用可能性と、そのロードマップについて議論を行う。

Event date： 2023.12

Language：English   Presentation type：Oral presentation (general)  

Country：United States  

Event date： 2023.12

Language：English   Presentation type：Oral presentation (general)  

Country：United States  

Event date： 2023.12

Language：English  

Venue：San Francisco   Country：United States  

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Event date： 2023.12

Language：English  

Venue：San Francisco   Country：United States  

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Event date： 2023.11

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.11

Language：English  

Venue：つくば国際会議場   Country：Japan  

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Event date： 2023.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：京都大学生存圏研究所   Country：Japan  

Event date： 2023.10

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.10

Language：Japanese  

Venue：大阪大学豊中キャンパス 南部ホール   Country：Japan  

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Event date： 2023.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Bangi   Country：Malaysia  

Event date： 2023.10

Language：English   Presentation type：Oral presentation (general)  

Country：Malaysia  

Event date： 2023.10

Language：English   Presentation type：Oral presentation (general)  

Country：Malaysia  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学青葉山キャンパス   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学青葉山キャンパス   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学青葉山キャンパス   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学青葉山キャンパス   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学青葉山キャンパス   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学青葉山キャンパス   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学青葉山キャンパス   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学青葉山キャンパス   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学青葉山キャンパス   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学青葉山キャンパス   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学青葉山キャンパス   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学青葉山キャンパス   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学青葉山キャンパス   Country：Japan  

Event date： 2023.9

Language：Japanese  

Venue：東北大学青葉山キャンパス   Country：Japan  

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Event date： 2023.9

Language：Japanese  

Venue：東北大学青葉山キャンパス   Country：Japan  

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Event date： 2023.9

Language：Japanese  

Venue：東北大学青葉山キャンパス   Country：Japan  

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Event date： 2023.9

Language：Japanese  

Venue：東北大学青葉山キャンパス   Country：Japan  

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Event date： 2023.8

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.8

Language：English  

Venue：SAPPORO   Country：Japan  

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Event date： 2023.7 - 2023.8

Language：English   Presentation type：Oral presentation (general)  

Country：Singapore  

Event date： 2023.7 - 2023.8

Language：English   Presentation type：Oral presentation (general)  

Country：Singapore  

Event date： 2023.5 - 2023.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Berlin   Country：Germany  

Event date： 2023.5 - 2023.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Berlin   Country：Germany  

Event date： 2023.5

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.5

Language：English   Presentation type：Oral presentation (general)  

Venue：幕張メッセ,千葉県幕張市   Country：Japan  

Event date： 2023.5

Language：English   Presentation type：Oral presentation (general)  

Venue：幕張メッセ,千葉県幕張市   Country：Japan  

Event date： 2023.5

Language：English   Presentation type：Oral presentation (general)  

Venue：幕張メッセ,千葉県幕張市   Country：Japan  

Event date： 2023.5

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.5

Language：English   Presentation type：Oral presentation (general)  

Venue：幕張メッセ,千葉県幕張市   Country：Japan  

Event date： 2023.5

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.5

Language：English   Presentation type：Oral presentation (general)  

Venue：幕張メッセ,千葉県幕張市   Country：Japan