Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Geophysical Research: Space Physics  

This study examines the seasonal distributions of simultaneous stratospheric concentric gravity waves (GWs) observed by the Atmospheric Infrared Sounders and concentric traveling ionospheric disturbances (TIDs) detected by the ground-based Global Navigation Satellite System Total Electron Content observations over the U.S. in 2022, to illustrate the mesoscale vertical coupling between the lower atmosphere and the ionosphere. We compared epicenters of GWs and TIDs in the stratosphere and ionosphere with tropospheric weather conditions and background winds in the thermosphere. Epicenters of concentric TIDs associated with stratospheric concentric GWs correspond to areas with high convective available potential energy over the central to eastern U.S. (∼60–110 (Formula presented.) W) in summer and over the southern U.S. (south of ∼40 (Formula presented.)) in spring and fall. Conversely, in fall to spring, epicenters over the northern U.S. (north of ∼40 (Formula presented.)) appeared south of regions with high extratropical cyclone activity. These findings suggest that convection was a primary source of concentric GWs driving TIDs over the continental U.S. during all four seasons, although the specific weather phenomena associated with the convection varied by season. Convection over the central to eastern U.S. in summer and the southern U.S. in spring could be linked to thunderstorms. In contrast, convection over the northern U.S. from fall through spring was likely linked to extratropical cyclones. We also found that concentric TIDs were linked to 66% of the stratospheric concentric GW events (195 events in total), underscoring the significant role of convection as a source of TIDs in the lower atmosphere and its contribution to the vertical coupling.

DOI： 10.1029/2024JA033429

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Earth and Space Science  

ICON observations were used to investigate local time (LT) and latitudinal variations of thermospheric meridional winds in the middle-high thermosphere (160–300 km) during quiet times in 2020 June and December. At middle-low latitudes (10°S–40°N), meridional winds were predominantly equatorward in the summer hemisphere while mostly poleward in the winter hemisphere. The meridional winds showed that the diurnal variation was dominant between ∼20°N and ∼40°N, but the semi-diurnal variation played a leading role at lower latitudes (below ∼20°N) during solstice months. Thermosphere-Ionosphere Electrodynamics General Circulation Model reproduced the ICON observed meridional wind variations qualitatively. A model diagnostic analysis shows that the pressure gradient force dominated the semi-diurnal variation of the winds, while the Coriolis force played a leading role in the diurnal variation in June. In December, LT variations of meridional winds were primarily driven by pressure gradient and ion drag forces. During both months, the vertical viscosity was important, tending to balance the effects of pressure gradients. Additionally, semi-diurnal variations of low-latitude meridional winds in June were more affected by upward propagating tides than those in December.

DOI： 10.1029/2024EA003880

Web of Science

Scopus

researchmap

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Geophysical Research: Space Physics  

In this study, we compare responses of the thermosphere and ionosphere to a planet encircling dust event in 2018 (PEDE 2018) occurred at the beginning of June 2018, a rare event last observed in 2007. Using the data from NGIMS (Neutral Gas and Ion Mass Spectrometer) instrument onboard MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft, we examine wave signatures and their spectral changes of three neutral species (O, Ar, CO2) and three ion species (O+, O2+, CO2+). Compared to low-dust period, the following salient features stand out: (a) Wave activities (amplitudes) are significantly enhanced in the neutral species, but with smaller enhancement in the ion species; (b) The apparent wavelengths in the neutrals shift and broaden from a range of 50–300 km to 80–400 km, with dominant wavelength shifting from 100 to 200 km; (c) The apparent wavelengths in the ions shift and broaden from a range of 80–300 km to 100–400 km, with dominant wavelength shifting from 150 km to 250–300 km; (d) The correlations among the wavelength distributions of various species are high with correlation coefficient above 0.57 during low-dust period and above 0.69 during PEDE 2018. These observed changes in wave signatures likely reflect filtering effects caused by changes in the middle atmosphere circulation induced by the global dust storm.

DOI： 10.1029/2024JA033014

Web of Science

Scopus

researchmap

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Annales Geophysicae  

Understanding ionospheric dependence on solar activity is crucial for comprehension of the upper atmosphere. The response of the ionosphere to solar extreme ultraviolet (EUV) flux has previously been considered stable. Subsequent studies have revealed long-term changes that are not yet fully understood. This work evaluates the stability of the ionospheric F2 layer (NmF2) dependence on solar EUV indices throughout different solar cycles (SCs). Hourly values of the peak electron density of NmF2 from Juliusruh station (54.6° N, 13.4° E) are analyzed between 1957 and 2023. Geomagnetic perturbations are removed. Third-degree polynomial-fit models dependent on different solar EUV proxies (MgII, F30, and F10.7) are generated separately for each solar cycle, each season, and each local time (LT) hour. The saturation effect is visible in our data and starts at lower F30 values in the ascending phase than in the descending phase. A highly pronounced local time dependence in January with the R2 (goodness of the description for each fit) value being maximum around the noon hours has been observed. The correlation is highest for F30 and MgII, especially under winter noon conditions, supporting the findings of recent studies that they are the best solar flux proxies for describing the NmF2 dependence at all LT hours. Most importantly, the response of NmF2 to solar flux shows a clear long-term change as the slopes of the model curves decrease with time for each solar cycle. Between SC20 and SC24, the observed decrease is consistently higher than 2.9 % per decade, reaching 4.4 % per decade at 90 sfu between 1964 and 2019. Copyright:

DOI： 10.5194/angeo-43-73-2025

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Space Weather and Space Climate  

This study explores the meteorological source and vertical propagation of gravity waves (GWs) that drive daytime traveling ionospheric disturbances (TIDs), using the specified dynamics version of the SD-WACCM-X (Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension) and the SAMI3 (Sami3 is Also a Model of the Ionosphere) simulations driven by SD-WACCM-X neutral wind and composition. A cold weather front moved over the northern-central USA (90'100 W, 35'45 N) during the daytime of 20 October 2020, with strong upward airflow. GWs with ~500'700 km horizontal wavelengths propagated southward and northward in the thermosphere over the north-central USA. Also, the perturbations were coherent from the surface to the thermosphere; therefore, the GWs were likely generated by vertical acceleration associated with the cold front over Minnesota and South Dakota. The convectively generated GWs had almost infinite vertical wavelength below ~100 km due to being evanescent. This implies that the GWs tunneled through their evanescent region in the middle atmosphere (where a squared vertical wavenumber is equal to or smaller than 0) and became freely propagating in the thermosphere and ionosphere. Medium-scale TIDs (MSTIDs) also propagated southward with the GWs, suggesting that the convectively generated GWs created MSTIDs.

DOI： 10.1051/swsc/2024036

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Geophysical Research: Space Physics  

Understanding the temporal and spatial variations in the ideal inert tracer helium can provide insight into the dynamic evolution of the thermosphere. The magnitude of the thermospheric winter helium bulge was inversely correlated with the level of solar activity. However, this feature has been found to be not reproduced by the Thermosphere-Ionosphere Electrodynamic General Circulation Model (TIEGCM), and the associated physical mechanisms remain unknown. Using the Thermosphere-Ionosphere-Mesosphere Electrodynamic General Circulation Model (TIME-GCM), we found that mesospheric gravity wave drag (GWD) is a factor contributing to this inverse correlation. Specifically, the summer-to-winter circulation in thermosphere becomes the main cause of the helium bulge, as mesospheric GWD can play a role in strengthening this circulation. The GWD contributions to temperature change below the lower thermosphere do not depend prominently on solar activity. However, because the temperature impacts on the pressure gradient force are height-integrated according to the background temperature of the neutral gas, the higher background temperature in the thermosphere at the solar maximum corresponds to a relatively weaker response in pressure gradient force in the thermosphere. Therefore, the response of the thermospheric circulation that might be expected to accompany increasing solar activity is suppressed due to the influence of mesospheric GWD, which results in a decrease in the magnitude of the winter helium bulge with increasing solar activity. Thus, our results demonstrated that lower atmosphere forcing can play a significant role in the response of thermospheric helium to solar activity.

DOI： 10.1029/2024JA033189

Web of Science

Scopus

researchmap

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

Abstract

Tidal signatures in sporadic E (Es) layer have been confirmed by observations and simulations. However, the effect of gravity waves (GWs) on the Es layer formation process has not yet been fully understood. In this paper, the modulation of Es layers by GWs is examined through numerical simulations, in which a physics‐based model of Es layer is forced by neutral winds from the High Altitude Mechanistic General Circulation Model that can resolve GWs with horizontal wavelengths longer than 156 km (λ_h > 156 km). Comparison of the simulation results with and without the GWs (1,350 km > λ_h > 156 km) forcing reveals that the inclusion of GWs leads to short‐period (1.2–3 hr) density perturbations in Es layers, which are also seen in ground‐based ionosonde observations. At a given time, the metallic ion density at altitudes between 120 and 150 km can either increase (by up to ∼+600%) or reduce (by up to −90%) in response to GW forcing. The relative density perturbations are smaller (by up to 60%) between 90 and 120 km altitude. It is also found that the GW effect on the metallic ion density relates to the longitude, which is mostly explained by the geographical distribution of GWs activity in the mesosphere and lower thermosphere region. The longitudinal variation of the background geomagnetic field plays only a secondary role.

DOI： 10.1029/2023EA003030

Web of Science

Scopus

researchmap

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

DOI： 10.5194/egusphere-egu23-12894

researchmap

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

DOI： https://doi.org/10.1029/2022SW003323

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

To assess the impacts of the tropospheric ozone modulation due to El Niño on tides, we performed two simulations by using the Ground-to-topside Atmosphere Ionosphere model for Aeronomy model: zonally symmetric ozone density and longitudinal ozone variation of an El Niño pattern. Our results show that the ozone modulation strengthens (attenuates) the first symmetric mode of the DW2 (D0 and DW1) tide by ∼+5% (∼−1% and ∼−4%) from ∼20 to ∼100 km altitudes on average. These responses are probably attributed to the tropospheric ozone modulation. These responses are reasonable because both the ozone modulation and these first modes have a peak at the equator. Also, the vertical wavelengths of the first modes are about twice as long as the vertical thickness of the ozone modulation. Our results suggest that the ozone modulation due to El Niño influences the diurnal tides by a few percent because of the ozone modulation spatial structure.

DOI： 10.1029/2023GL102790

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Frontiers in Astronomy and Space Sciences  

The Earth’s atmosphere near both the geographic and magnetic equators and at altitudes between 120 and 200 km is called the low-latitude valley region (LLVR) and is among the least understood regions of the ionosphere/thermosphere due to its complex interplay of neutral dynamics, electrodynamics, and photochemistry. Radar studies of the region have revealed puzzling daytime echoes scattered from between 130 and 170 km in altitude. The echoes are quasi-periodic and are observed in solar-zenith-angle dependent layers. Populations with two distinct types of spectral features are observed. A number of radars have shown scattering cross-sections with different seasonal and probing-frequency dependencies. The sources and configurations of the so-called 150-km echoes and the related irregularities have been long-standing riddles for which some solutions are finally starting to emerge as will be described in this review paper. Although the 150-km echoes were discovered in the early 1960s, their practical significance and implications were not broadly recognized until the early 1990s, and no compelling explanations of their generation mechanisms and observed features emerged until about a decade ago. Now, more rapid progress is being made thanks to a multi-disciplinary team effort described here and recent developments in kinetic simulations and theory: 18 of 27 riddles to be described in this paper stand solved (and a few more partially solved) at this point in time. The source of the irregularities is no longer a puzzle as compelling evidence has emerged from simulations and theory, presented since 2016 that they are being caused by photoelectrons driving an upper hybrid plasma instability process. Another resolved riddle concerns the persistent gaps observed between the 150-km scattering layers—we now understand that they are likely to be the result of enhanced thermal Landau damping of the upper hybrid instability process at upper hybrid frequencies matching the harmonics of the electron gyrofrequency. The remaining unsolved riddles, e.g., minute-scale variability, multi-frequency dependence, to name a few, are still being explored observationally and theoretically—they are most likely unidentified consequences of interplay between plasma physics, photochemistry, and lower atmospheric dynamic processes governing the LLVR.

DOI： 10.3389/fspas.2023.1091319

Web of Science

Scopus

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Journal of Geophysical Research: Space Physics  

At high-latitudes, diurnal and semidiurnal variations of temperature and neutral wind velocity can originate both in the lower atmosphere (UV or infrared absorption) and in the thermosphere-ionosphere (ion convection, EUV absorption). Determining the relative impact of different forcing mechanisms gives insight to the vertical coupling in the ionosphere. We analyze measurements from the incoherent scatter radar (ISR) facility operated by the EISCAT Scientific Association. They are complemented by meteor radar data and compared to global circulation models. The amplitudes and phases of tidal oscillations are determined by an adaptive spectral filter (ASF). Measurements indicate the existence of strong semidiurnal oscillations in a two-band structure at altitudes ≲110 and ≳130 km, respectively. Analysis of several model runs with different input settings suggest the upper band to be forced in situ while the lower band corresponds to upward-propagating tides from the lower atmosphere. This indicates the existence of an unexpectedly strong, in situ forcing mechanism for semidiurnal oscillations in the high-latitude thermosphere. It is shown that the actual transition of tides in the altitude region between 90 and 150 km is more complex than described so far.

DOI： 10.1029/2022JA030861

Web of Science

Scopus

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Journal of Geophysical Research: Space Physics  

The Constellation Observing System for Meteorology, Ionosphere, and Climate radio occultation S4 indices measurements are used to investigate the global structure and seasonal variations of tidal components in the sporadic-E (Es) layer. The diurnal tidal amplitude in the Es layer intensity and occurrence rate shows a wave-4 longitudinal structure, which is due to the diurnal tidal components of zonal wave numbers s = −3 (eastward, DE3). The wave-4 longitudinal pattern is also observed in the semidiurnal tide during spring and winter, which mostly results from the combination of semidiurnal components of zonal wave numbers s = −2 (eastward, SE2), s = 2 (westward, SW2). In addition, the semidiurnal tidal amplitude in Es layers presents obvious seasonal variability, and it dominates in the northern hemisphere during spring and summer and in the southern hemisphere during autumn and winter. Furthermore, the total semidiurnal tidal amplitude in Es layers in the northern hemisphere is greater than that in the southern hemisphere. Another important finding is that the diurnal tidal pattern at the lower altitude (below 102 km) Es layer is different from that of the higher altitude (above 102 km) Es layer and is also different from that of wind, which supports that the wind shear theory is inapplicable for the Es layer formation at low altitude proposed by many researchers.

DOI： 10.1029/2022JA030711

Web of Science

Scopus

researchmap

Language：Others  

DOI： 10.5194/acp-2022-534

researchmap

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Journal of Geophysical Research: Space Physics  

We explored mechanisms for the thermospheric zonal mean wind responses to doubled CO2 concentration through investigating the zonal mean momentum balance in the thermosphere using GAIA model simulations in June. The analysis shows that ion drag, molecular viscosity, and meridional pressure gradient force vary 3–20 times more than the other forces due to the doubled CO2 concentration. The three forces strongly attenuate each other; consequently, the increase in zonal mean zonal ion drag dominantly strengthens the southward wind (∼15 ms−1 at maximum) in the northern (summer) hemisphere and latitudes north of 35 (Formula presented.) S. This strengthened ion drag was attributed to increased ion density/relative velocity between ions and neutral particles in the northern/southern hemisphere. Southward of 35 (Formula presented.), the zonal pressure gradient force and the meridional advection of zonal wind strengthen the southward wind by 4–12 ms−1 in total. On the other hand, the zonal wind is mainly altered by increased meridional pressure gradient force (∼15 ms−1 at maximum) caused by a latitudinally asymmetric response of the thermosphere density to increasing CO2 concentration. Our results suggest that the increased ion density in the northern hemisphere is the underlying trigger for the wind responses to increasing CO2 concentration. Furthermore, we show that the meridional advection was mainly (∼70%) due to that of the DW1 tidal component.

DOI： 10.1029/2022JA030643

Web of Science

Scopus

researchmap

Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/essoar.10511964.1

researchmap

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

The 3 February 2022 launch of 49 of SpaceX's Starlink satellites has provided a fascinating example of how even modest space weather can have significant practical and financial consequences. Enhanced atmospheric drag associated with a minor geomagnetic storm led to the loss of the majority of the 49 launched satellites. Although the 36th launch by SpaceX in the past 3 years, it was the first that experienced stormy space weather. We expect more stormy space weather as Solar Cycle 25 ramps up toward its peak expected in 2025. A subsequent Starlink launch on 21 February used a higher initial orbit at 300 km, reducing the payload from 49 to 46 satellites, and can be considered an agile response to the space weather losses experienced 2 weeks earlier. Lessons to be learned by the space industry and the space weather community are discussed, including a better dialog, nuanced understanding of space weather risks associated with modest events, but also an opportunity to investigate the space environment in relatively unexplored regions such as very low and high low Earth orbits.

DOI： 10.1029/2022SW003074

Web of Science

Scopus

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

DOI： 10.1029/2021JA030071

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

DOI： 10.1002/essoar.10510636.1

researchmap

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

DOI： 10.1029/2021JA030071

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

DOI： 10.1029/2021GL097651

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

DOI： 10.1029/2021GL097651

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

DOI： 10.1029/2021SW002883

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

DOI： 10.5194/dach2022-84

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

DOI： 10.5194/dach2022-81

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

DOI： 10.1029/2021SW003000

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

DOI： 10.1029/2021JA029222

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

DOI： 10.5194/acp-21-13855-2021

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

Ground-based and satellite observations have shown that the tidal component DW1 in
the equatorial mesosphere and lower thermosphere (MLT) was enhanced in July–October 2015, which was an intense El Niño year. This enhancement is reproduced in the 21 years reanalysis-driven model simulation by the Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy (GAIA). Our analysis shows the (1,1) Hough mode dominates this tidal enhancement, and its peak amplitude was 7.4 K (74%) higher than that under neutral (non-ENSO) conditions at 90 km. The corresponding tidal heating was found to increase by 0.4 mWkg−1 (5%), which can explain 0.5 K (7%) of the (1,1) enhancement. To explain the remaining 6.9 K (93%) of the enhancement, we quantitively examined the upward propagation condition by calculating the vertical wavenumber and the latitudinal shear of the zonal wind. The analysis reveals that the vertical wavenumber between 18 and 60 km was one standard deviation smaller than
that under neutral conditions. The latitudinal zonal wind shear also decreased at 18 N/S° in 18–30 km. These results suggest smaller dissipation and damping of the (1,1) mode during its upward propagation, which dominantly contributed to the tidal enhancement at 90 km altitude. This decrease in the vertical wavenumber and the wind shear can be reasonably explained by the eastward phase of the quasi-biennial oscillation (QBO) in the lower stratosphere. This study suggests that the overlapping of the 2015 El Niño with the eastward phase of the QBO induced the large enhancement of the DW1.

DOI： 10.1029/2021ja029342

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

DOI： 10.1029/2021GL092537

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

DOI： 10.1002/9781119815631.ch15

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

Sudden Stratospheric Warming Impacts on the Ionosphere– Thermosphere System: A Review of Recent Progress

DOI： 10.1002/9781119815617.ch16

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

DOI： 10.1029/2020JA028729

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

DOI： 10.1029/2020JA028607

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

We examine impacts of geomagnetic activity (GA) on CO -driven trend in the ionosphere and thermosphere using the Ground-to-topside Atmosphere Ionosphere model for Aeronomy whole atmosphere model. The model reveals three salient features. (1) Geomagnetic activities usually weakens the CO -driven trend at a fixed altitude. Among the IT parameters analyzed, the thermosphere mass density is the most robust indicator for CO cooling effect even with GA influences. (2) Geomagnetic activities can either strengthen or weaken the CO -driven trend in hmF2 and NmF2, depending on local time and latitudes. This renders the widely used linear fitting methods invalid for removing geomagnetic effects from observations. (3) An interdependency exists between the efficiency of CO forcing and geomagnetic forcing, with the former enhances at lower GA level, while the latter enhances at higher CO concentration. This could imply that the CO -driven trend would accelerate in periods of declining GA, while magnetic storms may have larger space weather impacts in the future with increasing CO . These findings provide a preliminary model framework to understand interactions between the CO forcing from below and the geomagnetic forcing from above. 2 2 2 2 2 2 2 2 2

DOI： 10.1029/2020ja028607

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

DOI： 10.1029/2020JA028729

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

<title>Abstract</title>
The technique of spherical elementary current systems (SECS) is a powerful way to determine ionospheric and field-aligned currents (FAC) from magnetic field measurements made by low-Earth-orbiting satellites, possibly in combination with magnetometer arrays on the ground. The SECS method consists of two sets of basis functions for the ionospheric currents: divergence-free (DF) and curl-free (CF) components, which produce poloidal and toroidal magnetic fields, respectively. The original CF SECS are only applicable at high latitudes, as they build on the assumption that the FAC flow radially into or out of the ionosphere. The FAC at low and middle latitudes are far from radial, which renders the method inapplicable at these latitudes. In this study, we modify the original CF SECS by including FAC that flow along dipolar field lines. This allows the method to be applied at all latitudes. We name this method dipolar elementary current systems (DECS). Application of the DECS to synthetic data, as well as Swarm satellite measurements are carried out, demonstrating the good performance of this method, and its applicability to studies of ionospheric current systems at low and middle latitudes.

DOI： 10.1186/s40623-020-01284-1

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

DOI： 10.1029/2019JA027721

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

DOI： 10.1029/2020JA027789

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

DOI： https://doi.org/10.1186/s40623-020-01284-1

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

DOI： 10.1029/2021GL092537

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

DOI： https://doi.org/10.1029/2019JA027721

Other Link： https://doi.org/10.1029/2019JA027721

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

DOI： 10.1029/2020GL087413

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

Thermosphere cooling is a known effect of increasing CO2 in the atmosphere. In this study, we explore the changes of thermosphere circulation and tides in the cooled thermosphere via a doubled CO2 numerical experiment using the Ground-to-topside Atmosphere Ionosphere model for Aeronomy (GAIA). The results reveal three major features. (1) The thermosphere cools about 10 K more around solstices than equinoxes, more at the summer pole than the winter pole. (2) The meridional circulation shifts downward and strongly accelerates by 5-15 m s(-1). (3) The tidal activity experiences dramatic changes, with a 40-60% reduction in the semidiurnal tides (SW2) throughout the thermosphere but an 30-50% enhancement in diurnal tides (DW1) below 200 km altitude. The nonmigrating tide DE3 has only minor changes. These changes in temperature, meridional circulation, and tides are persistent features in all seasons and can profoundly affect the spatial distribution and diurnal cycles of the ionospheric responses to CO2 doubling via atmosphere composition and electrodynamics.

DOI： 10.1029/2020GL087413

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

DOI： 10.1029/2020GL087078

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

Sunspot observations by Hisako Koyama: 1945–1996

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

DOI： 10.1029/2020GL087078

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

DOI： doi:10.1093/mnras/stz3345

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

DOI： 10.1186/s40623-019-1009-7

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

DOI： 10.1029/2019GL084951

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

With simultaneous ionospheric measurements from ROCSAT-1 satellite and ground ionosondes/GPS receivers, three cases of concurrent plasma blobs and bubbles in the same magnetic meridian were observed around 22:30 LT in Asian-Oceanian sector during solar maximum. Two cases were observed: equatorial spread F (ESF) over Vanimo station (geog. 2.7 degrees S, 141.3 degrees E; geom. 11.2 degrees S, 146.2 degrees W) and plasma blobs around 8.0 degrees S (geom.) on 1 June and 6 October 2003. The other case observed equatorial spread F over Hainan station (geog. 19.5 degrees N, 109.1 degrees E; geom. 9.1 degrees N, 179.1 degrees W) and plasma blob near the dip equator on 8 March 2004. Plasma blobs were all observed near 600-km height near the equator. Equatorial spread F and amplitude scintillations from the ground stations were observed near the same magnetic meridian, indicating the existence of bubbles. Considering that both plasma bubbles and blobs are field-aligned elongated structures, magnetic field line mapping shows that in the two cases at Vanimo, blobs were above bubbles, providing direct observational evidence for blob formation in the intermediate stage of plasma bubble evolution; in the case at Hainan, the blob and bubble were likely at similar height, and it could be generated by gravity wave.

DOI： 10.1029/2018JA026373

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

DOI： 10.1029/2019GL083629

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

The seeding mechanism of equatorial plasma bubbles (EPBs) in the ionosphere has not been fully understood for several decades. Before investigating the complex seeding process by atmospheric gravity waves, which have been considered as a possible candidate, we investigate the vertical neutral wind effect on the EPB seeding by making the numerical simulation setup as simple as possible. It is presented that the vertical wind over the dip equator with an amplitude of as low as 5 m/s can seed EPBs effectively. The upward wind reduces the eastward current and produces the eastward polarization electric field, so that the bottomside F region pushed by the upward wind is going to form upwellings and penetrate into the topside F region accelerated by the Rayleigh-Taylor instability. It is suggested that the vertical wind perturbations driven by gravity waves should play an important role in seeding EPBs.

DOI： 10.1029/2019GL083629

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

DOI： 10.5194/angeo-37-235-2019

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

DOI： 10.5194/angeo-37-235-2019

Language：Others  

El Nino-Southern Oscillation effect on ionospheric tidal/SPW amplitude in 2007-2015 FORMOSAT- 3/COSMIC observations (vol 71, 35, 2019)

DOI： 10.1186/s40623-019-1025-7

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

DOI： https://doi.org/10.1029/2018JA025634

Language：Others  

Nino-Southern Oscillation effect on ionospheric tidal/SPW amplitude in 2007-2015 FORMOSAT-3/COSMIC observations

DOI： 10.1186/s40623-019-1009-7

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

DOI： 10.1029/2019GL082155

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

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

DOI： 10.1029/2018JA025634

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

DOI： https://doi.org/10.1016/j.asr.2018.12.042

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

DOI： 10.1029/2018JA026373

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

DOI： 10.1186/s40623-018-0832-6

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

DOI： https://doi.org/10.1186/s40623-018-0916-3

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

DOI： 10.1029/2018GL077898

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

DOI： 10.1002/2017JA025165

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

DOI： 10.1186/s40623-017-0704-5

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

DOI： 10.1002/2017SW001704

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

DOI： 10.1002/2017JA024146

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

DOI： 10.1002/2017GL073855

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

DOI： 10.1002/2017SW001618

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

DOI： 10.1088/1742-6596/852/1/012015

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

DOI： 10.1002/2017JA024011

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

DOI： 10.1002/2016JA023776

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

DOI： 10.1002/2016JA023684

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

DOI： 10.1002/ 2016JA023448

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

DOI： 10.1002/2015JA022076

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

DOI： 10.1002/2016JA022938

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

DOI： 10.1038/srep-18895

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

DOI： doi:10.1186/s40562-016-0038-3

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

DOI： http://dx.doi.org/10.1016/j.asr.2015.08.030

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

DOI： 10.1186/s40623-016-0455-8

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

DOI： 10.1002/2015GL065671

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： doi:10.1002/2014JA020752

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

DOI： 10.1002/2014JA020014

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

DOI： http://www.earth-planets-space.com/content/66/1/146

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

DOI： 10.5194/angeo-32-1145-2014

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

DOI： 10.1002/2014JA020255

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

DOI： 10.1002/2014SW001110

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

DOI： 10.1002/2014JA020222

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

DOI： 10.1002/2014JA019843

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

DOI： 10.1002/2013JA019742

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： 10.1016/j.asr.2013.11.052

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

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

DOI： 10.1002/grl.50146

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

DOI： doi:10.1002/jgra.50355

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

DOI： doi:10.1002/jgra.50144

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

DOI： 10.1029/2012JA018116

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

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

DOI： 10.1029/2012JA018045

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

DOI： 10.1029/2011JA017373

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

DOI： 10.1016/j.jastp.2011.12.002

Language：English  

DOI： 10.1007/978-94-007-0326-1_22

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

DOI： 10.1029/2011JA016607

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

DOI： 10.1029/2010JA016399

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

DOI： 10.1007/s11214-011-9798-4

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

DOI： 10.1029/2011GL047898

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

DOI： 10.1029/2010JA016634

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

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

DOI： 10.1029/2010RS004431

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

DOI： 10.1029/2011GL047255

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

DOI： 10.1029/2010JA016315

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

DOI： 10.1029/2010JA016235

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

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

DOI： 10.1029/2009JA015147

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

DOI： 10.1029/2010GL042855

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

DOI： 10.1029/2009JA014689

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

DOI： 10.1029/2009JA014439

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

DOI： 10.1029/2009GL039865

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

DOI： 10.1029/2009GL038165

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

DOI： 10.1029/2009GL037377

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

DOI： 10.1029/2008JA013027

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

DOI： 10.1029/2007JA012313

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

DOI： 10.1029/2005JA011415

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

DOI： 10.1029/2007JA012616

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

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

DOI： 10.1029/2006JA012199

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

DOI： 10.1029/2004JA010908

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

DOI： 10.1029/2004JA010741

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  

DOI： 10.1016/j.watres.2025.123922

PubMed

Language：English  

DOI： 10.5194/egusphere-egu25-7418

researchmap

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

The measurement of virtual height of the sporadic E layer (h'Es) is very sensitive to the type of ionosonde used and the calibration processes. The ionosondes used by the national institute of communication and technology (NICT) has changed several times in the past, resulting in large differences in h'Es before and after the change. We propose a simple method to calibrate h'Es. We used the data of ionosonde observations at four stations, i.e., Wakkanai (45.16 degrees N, 141.75 degrees E), Tokyo (35.71 degrees N, 139.49 degrees E), Yamagawa (31.20 degrees N, 130.62 degrees E), Okinawa (26.68 degrees N, 128.15 degrees E) to calibrate the latest ionosondes VIPIR2, which were installed in May 2017. We carried out the analysis by applying the double-reflection method to the original ionogram images between 2017 and 2021. By developing an automated image detecting algorithm, we were able to process a large amount of data and achieve a calibration with high accuracy. As a result, it was found that the current VIPIR2 data had an offset of 26-28 km.

DOI： 10.1186/s40623-025-02138-4

Web of Science

Scopus

researchmap

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

Abstract

Sporadic E (Es) layers are plasma irregularities significantly affecting radio communication and navigation systems. And, their dominant formation mechanism at mid‐latitudes, known as the wind shear theory, suggests that they serve as indicators of the atmosphere‐ionosphere coupling processes in the mesosphere and lower thermosphere region. On 15 January 2022, the Hunga Tonga‐Hunga Ha'api submarine volcanic eruption provided a unique opportunity to investigate the Es layer responses to lower atmospheric perturbations. Using the FORMOSAT‐7/COSMIC‐2 radio occultation and ground‐based ionosonde observations, this study reveals the spatial‐temporal behaviors of the Es layers after the Hunga volcanic eruption. The results show that significant Es layer perturbations occurred over the northwest of the epicenter ∼4 hr after the eruption and lasted for approximately ∼22 hr. We also calculated the geographical distribution of the vertical ion convergence (VIC) using neutral winds obtained from the Michelson Interferometer for Global High‐resolution Thermospheric Imaging on the Ionospheric Connection Explorer (ICON) satellite. A comparison of the geographical distribution of positive VIC and Es layer perturbations shows a good agreement, which indicates that the enhanced Es layers are caused by strong VIC associated with the atmospheric perturbations due to the eruption. This study presents observational evidence for coupling between the Es layer and lower atmospheric perturbations, which can be helpful for understanding the occasionality and variability of Es layer occurrence.

DOI： 10.1029/2023SW003837

Web of Science

Scopus

researchmap

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

Abstract

We use multi‐year observations of cross‐track winds (u) from the CHAllenging Minisatellite Payload (CHAMP) and the Gravity Field and Steady State Ocean Circulation Explorer (GOCE) to calculate third‐order structure functions in the thermosphere as a function of horizontal separation (s). They are computed using the mean (〈δu³〉) and the median and implemented over non‐polar satellite paths in both hemispheres. On height averages, 〈δu³〉 is shown to scale with s² for s ≃ 80–1,000 km, in agreement with equivalent estimates in the lower atmosphere from aircraft observations. Conversely, follows an s³ power law for almost the whole s range, consistent with the two‐dimensional turbulence scaling law for a direct enstrophy cascade. These scaling laws appear independent of winds in distinct atmospheric regions. Furthermore, the functions are predominantly positive, indicating a preferential cyclonic motion for the wind.

DOI： 10.1029/2024GL108367

Web of Science

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2024SW004016

Web of Science

researchmap

Language：English  

DOI： 10.22541/essoar.171699813.38713303/v1

researchmap

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Earth and Space Science  

Joule heating is one of the main energy inputs into the thermosphere-ionosphere system. Precise modeling of this process is essential for any space weather application. Existing thermosphere-ionosphere models tend to underestimate the actual Joule heating rate quite significantly. The Thermosphere-Ionosphere-Electrodynamics General-Circulation-Model applies an empirical scaling factor of 1.5 for compensation. We calculate vertical profiles of Joule heating rates from approximately 2,220 hr of measurements with the EISCAT incoherent scatter radar and the corresponding model runs. We investigate model runs with the plasma convection driven by both the Heelis and the Weimer model. The required scaling of the Joule heating profiles is determined with respect to the Kp index, the Kan-Lee merging electric field EKL, and the magnetic local time. Though the default scaling factor of 1.5 appears to be adequate on average, we find that the required scaling varies strongly with all three parameters ranging from 0.46 to ∼20 at geomagnetically disturbed and quiet times, respectively. Furthermore, the required scaling is significantly different in runs driven by the Heelis and Weimer model. Adjusting the scaling factor with respect to the Kp index, EKL, the magnetic local time, and the choice of convection model would reduce the difference between Joule heating rates calculated from measurement and model plasma parameters.

DOI： 10.1029/2023EA003447

Web of Science

Scopus

researchmap

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

DOI： 10.1029/2024SW003929

Web of Science

Scopus

researchmap

Language：Japanese   Publisher：宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS)  

レポート番号: Ⅳ-1

CiNii Research

Language：English   Publisher：Advances in Space Research  

Equatorial Plasma Bubbles (EPBs) are zones characterized by fluctuations in plasma densities which form in the low-latitude ionosphere primarily during the post-sunset. They subject radio signals to amplitude and phase variabilities, affecting the functioning of technological systems that utilize the Global Navigation Satellite Systems (GNSS) signals for navigation. Thus, understanding EPB occurrence patterns and morphological features is vital for mitigating their effects. In this work, we employed two GNSS receivers and an All-Sky Imager (ASI) to conduct simultaneous observations on the morphology of EPBs over Brazil. The main objectives of the study were (1) to develop a Random Forest (RF) machine-learning model to estimate and predict the zonal drift velocities of EPBs, and (2) to compare the model predictions with actual EPB drifts inferred from the two instruments, as well as zonal neutral wind speeds obtained from the Horizontal Wind Model (HWM-14). In the model development, we utilized reliable EPB drift measurements made during geomagnetically quiet days between 2013 and 2017 in Brazil. The model predicted the velocities based on parameters including the day of the year, universal time, critical frequency of the F2 layer (foF2), solar and interplanetary indices. The correlation coefficients of 0.98 and 0.96 and RMSE values of 10.61 m/s and 10.06 m/s were obtained upon training and validation correspondingly. We evaluated the accuracy of the model in predicting EPB drifts on two geomagnetically quiet nights where an average correlation coefficient of 0.89 and an RMSE of 15.74 m/s were obtained. The predicted drifts, the zonal neutral wind velocities, and the GNSS and ASI velocity measurements were put into context for validation purposes. Overall, the velocities were comparable and ranged between ∼100 m/s and ∼30 m/s from the hours of 00 UT to 05 UT. The results confirmed the accuracy and applicability of the model, revealing the ionosphere-thermosphere coupling influence on the nocturnal propagation of EPBs under the full activation of the F region dynamo.

DOI： 10.1016/j.asr.2024.08.067

Web of Science

Scopus

Publisher：Advances in Space Research  

In this paper we carried out a numerical experiment using the Specified Dynamics mode of the Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension (SD-WACCM-X). One SD-WACCM-X run was with realistic Kp and F10.7 and the other with constant Kp and F10.7. By comparing the day-to-day variability of thermosphere mass density at 300 km (low earth orbit, LEO) and 120 km (reentry level) in these two runs, we find that the density variation at 300 km is mainly driven by geomagnetic and solar forcing while at 120 km it is exclusively controlled by the lower atmosphere. At LEO altitudes, during solar minimum and geomagnetic quiet days, the impact from the lower atmosphere is much smaller than the effect of solar and geomagnetic variations but is not negligible (5–10% vs 20%).

DOI： 10.1016/j.asr.2022.06.011

Web of Science

Scopus

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Atmospheric Chemistry and Physics  

Continuous wind measurements using partial-reflection radars and specular meteor radars have been carried out for nearly 2 decades (2004-2022) at middle and high latitudes over Germany (g1/4g54ggN) and northern Norway (g1/4g69ggN), respectively. They provide crucial data for understanding the long-Term behavior of winds in the mesosphere and lower thermosphere. Our investigation focuses on the summer season, characterized by the low energy contribution from tides and relatively stable stratospheric conditions. This work presents the long-Term behavior, variability, and trends of the maximum velocity of the summer eastward, westward, and southward winds. In addition, the geomagnetic influence on the summer zonal and meridional wind is explored at middle and high latitudes. The results show a mesospheric westward summer maximum located around 75gkm with velocities of 35-54gmgs-1, while the lower-Thermospheric eastward wind maximum is observed at g1/4g97gkm with wind speeds of 25-40gmgs-1. A weaker southward wind peak is found around 86gkm, ranging from 9 to 16gmgs-1. The findings indicate significant trends at middle latitudes in the westward summer maxima with increasing winds over the past decades, while the southward winds show a decreasing trend. On the other hand, only the eastward wind in July has a decreasing trend at high latitudes. Evidence of oscillations around 2-3, 4, and 6 years modulate the maximum velocity of the summer winds. In particular, a periodicity between 10.2 and 11.3 years found in the westward component is more significant at middle latitudes than at high latitudes, possibly due to solar radiation. Furthermore, stronger geomagnetic activity at high latitudes causes an increase in eastward wind velocity, whereas the opposite effect is observed in zonal jets at middle latitudes. The meridional component appears to be disturbed during high geomagnetic activity, with a notable decrease in the northward wind strength below approximately 80gkm at both latitudes.

DOI： 10.5194/acp-23-14871-2023

Web of Science

Scopus

researchmap

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Space Weather  

The media interest/coverage of space weather has been increasing as we approach solar maximum and the private space industry has grown significantly since the last significant solar maximum in 2000–2002. It is not uncommon for space weather media coverage to use hyperbole with frequent references to the infamous “Carrington event.” The implications of associating each of the many upcoming moderate-to-severe storms with the Carrington event are discussed, and we encourage the curbing of hyperbole whenever possible. While there is an excellent but small cohort of space weather researchers actively engaging with the media, we urge more (particularly early-to-mid career) to take advantage of media training resources and to join in. We also call for these efforts to be broadly supported by peers and institutions for the benefit of space weather as a discipline.

DOI： 10.1029/2023SW003819

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Earth, Planets and Space  

DOI： 10.1186/s40623-023-01893-6

Web of Science

Scopus

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Space Weather  

The monthly mean sunspot number has been larger in June–July 2023 than the double peak of solar cycle 24 (146 in February 2014 and 139 in November 2011) and brings us back to the sunspot level of solar cycle 23. However, the number of rocket launches, satellites in orbit and private space companies has increased dramatically in the past 20 years. Additionally, there is a growing interest for space exploration beyond Earth's orbit, to the Moon and beyond, which comes with higher risk of being affected by space weather. Here, we discuss some of these trends and the role of the journal to improve awareness of space weather impacts.

DOI： 10.1029/2023SW003702

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Earth and Planetary Physics  

At present, the main detection instruments for observing sporadic E (Es) layers are ground-based radars, dense networks of ground-based global navigation satellite system (GNSS) receivers, and GNSS radio occultation, but they cannot capture the whole picture of the horizontal structure of Es layers. This study employs the Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension model (WACCM-X 2.1) to derive the horizontal structure of the ion convergence region (HSICR) to explore the shapes of the large-scale Es layers over East Asia for the period from June 1 to August 31, 2008. The simulation produced the various shapes of the HSICRs elongated in the northwest−southeast, northeast−southwest, or composed of individual small patches. The close connection between Es layer critical frequency (foEs) and vertical ion convergence indicates that the HSICR is a good candidate for revealing and explaining the horizontal structure of the large-scale Es layers.

DOI： 10.26464/epp2023071

Web of Science

Scopus

researchmap

Publisher：Atmosphere  

Using a network of meteor radar observations, observational evidence of polar-to-tropical mesospheric coupling during the 2018 major sudden stratosphere warming (SSW) event in the northern hemisphere is presented. In the tropical lower mesosphere, a maximum zonal wind reversal (−24 m/s) is noted and compared with that identified in the extra-tropical regions. Moreover, a time delay in the wind reversal between the tropical/polar stations and the mid-latitudes is detected. A wide spectrum of waves with periods of 2 to 16 days and 30–60 days were observed. The wind reversal in the mesosphere is due to the propagation of dominant intra-seasonal oscillations (ISOs) of 30–60 days and the presence and superposition of 8-day period planetary waves (PWs). The ISO phase propagation is observed from high to low latitudes (60° N to 20° N) in contrast to the 8-day PW phase propagation, indicating the change in the meridional propagation of winds during SSW, hence the change in the meridional circulation. The superposition of dominant ISOs and weak 8-day PWs could be responsible for the delay of the wind reversal in the tropical mesosphere. Therefore, this study has strong implications for understanding the reversed (polar to tropical) mesospheric meridional circulation by considering the ISOs during SSW.

DOI： 10.3390/atmos14081302

Web of Science

Scopus

Language：Others  

DOI： 10.5194/egusphere-2023-1465

researchmap

Publisher：Frontiers in Astronomy and Space Sciences  

This brief report examines the ground-based total electron content (TEC) in Asian sector during August–October 2019, covering the period of a stratosphere sudden warming (SSW) occurred in Antarctica. The analysis reveals pronounced ionospheric day-to-day variability with distinct periodicities. The most dominant and long-lasting periodicities are quasi-10 days and quasi 14-day during September and October, while a quasi 6-day also present in September. The 10-day and 6-day TEC oscillations were attributed by previous studies solely to the Antarctic SSW while assuming negligible geomagnetic effects. By comparing co-located ground mesospheric wind observations, along with the interplanetary electric field (IEF) and geomagnetic activity (Kp index), we demonstrate that the quasi 14-day oscillation is mainly driven by low-level geomagnetic activities, while quasi-6 days oscillation is driven by mesospheric wind changes during the SSW. The 10-day oscillation, on the other hand, is driven by both IEF and mesospheric wind in September, but by IEF in October. These results demonstrate that low-level geomagnetic activities traditionally classified as “quiet conditions” can induce significant day-to-day oscillations in TEC, and their impacts should not be ignored when studying meteorological (e.g., SSWs) impacts on the ionosphere.

DOI： 10.3389/fspas.2023.1198739

Web of Science

Scopus

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Space Weather  

Recently, many in the space weather community have taken up the cause to advocate for an orphan among our own. It’s an important fight—for ground-based sensor networks. Although ground-based sensors are used across all disciplines of space weather, in terms of long-term support, they have no single clear home in any United States agency or department. This has resulted in an ongoing struggle throughout the community to maintain important space weather sensors and networks.

DOI： 10.1029/2023SW003529

Scopus

researchmap

Language：Others  

DOI： 10.5194/egusphere-egu23-8579

researchmap

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Space Weather  

In this paper, the Earth's sporadic-E (Es) layer vertical motion is investigated by using an image processing technique for automatic scaling ionograms from Mohe (122.37°E, 53.50°N, dip angle 71°), Beijing (116.25°E, 40.25°N, dip angle 59°), Wuhan (114.61°E, 30.53°N, dip angle 46°) and Fuke (109.13°E, 19.52°N, dip angle 27°). Es traces descend with different periodicities, indicating tidal modulation to Es layers. Comparing winds from a combination of the Ionospheric Connection Explorer/Michelson Interferometer for Global High-Resolution Thermospheric Imaging and meteor radar measurements with Es layers, we find that Es traces at high altitudes (above 110 km) rapidly move down in accordance with the descent of the wind shear nulls, which indicates the important role of the tides in the formation and descent of the Es layer at high altitude. The lower-lying Es layers, however, do not descend with the wind shear null, but stay at the bottom of the E region (∼100 km) for a long time, which cannot be explained by tidal wind shear theory. In addition, the time duration of the Es layers staying at low latitudes increases with the decreasing latitude. Simulation results demonstrate that the low altitude tailing Es layer is dominated by the dramatically enhanced collision frequency at the lower height of the mesosphere and the lower thermosphere region.

DOI： 10.1029/2022SW003323

Web of Science

Scopus

researchmap

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Journal of Geophysical Research: Space Physics  

In this study, we focused on the influences of mesospheric gravity wave drag on the winter helium bulge in the thermosphere. The related physical mechanisms are investigated based on the three-dimensional physics-based Thermosphere-Ionosphere-Mesosphere Electrodynamic General Circulation Model. The simulation results suggested that the mesospheric gravity wave drag can contribute to the high amplitude of winter helium bulge due to the intensified summer-to-winter circulation in the thermosphere. It was found that the meridional pressure gradient force, which dominates the generation of thermospheric large-scale circulation, shows an increase when the effect of mesospheric gravity wave drag is considered. The change in thermospheric pressure force is attributed to the mesospheric gravity wave drag related winter-to-summer flow in the lower thermosphere. This intensified summer-to-winter circulation in the thermosphere leads to the decrease and increase of helium concentration in summer and winter, respectively, which thus contributes to the thermospheric winter helium bulge under the effects of mesospheric gravity wave drag.

DOI： 10.1029/2022JA031022

Web of Science

Scopus

researchmap

DOI： 10.1002/essoar.10512999.1

researchmap

DOI： 10.1088/1361-6587/ac97be

Web of Science

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Space Weather  

This editorial aims to improve awareness of the current best practices in open research, and stimulate discussion on the practical implementation of AGU's data and software policy in key areas of space weather research. We also further aim to encourage authors to take additional steps to ensure clear credit to all contributors to the work, whether that is underlying data, key software, or direct contributions to the manuscript.

DOI： 10.1029/2022SW003371

Web of Science

Scopus

researchmap

Publisher：Space Weather  

The upper boundary height of the traditional community general circulation model of the ionosphere-thermosphere system is too low to be applied to the topside ionosphere/thermosphere study. In this study, the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model (NCAR-TIEGCM) was successfully extended upward by four scale heights from 400–600 km to 700–1,200 km depending on solar activity, named TIEGCM-X. The topside ionosphere and thermosphere simulated by TIEGCM-X agree well with the observations derived from a topside sounder and satellite drag data. In addition, the neutral density, temperature, and electron density simulated by TIEGCM-X are morphologically consistent with the NCAR-TIEGCM simulations before extension. The latitude-altitude distribution of the equatorial ionization anomaly derived from TIEGCM-X is more reasonable. During geomagnetic storm events, the thermospheric responses of TIEGCM-X are similar to NCAR-TIEGCM. However, the ionospheric storm effects in TIEGCM-X are stronger than those in NCAR-TIEGCM and are even opposites at some middle and low latitudes due to the presence of more closed magnetic field lines. Defense Meteorological Satellite Program observations prove that the ionospheric storm effect of TIEGCM-X is more reasonable. The well-validated TIEGCM-X has significant potential applications in ionospheric/thermospheric studies, such as the responses to storms, low-latitude dynamics, and data assimilation.

DOI： 10.1029/2022SW003227

Web of Science

Scopus

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union ({AGU})  

The next decadal survey process for space and solar physics will start soon with white papers due during the second half of 2022 and the committees and panels working over all of 2023. Space weather science and operations will play an essential role in this survey. Therefore, the community is invited to prepare white papers and get involved in advancing space weather research and capabilities in the upcoming decades. A summary of the recommendations related to space weather from the last two decadal surveys is also provided.

DOI： 10.1029/2022SW003181

Web of Science

Scopus

researchmap

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

DOI： 10.1029/2022SW003116

Language：Japanese  

第4回観測ロケットシンポジウム（2022年3月14-15日. ハイブリッド開催（JAXA相模原キャンパス& オンライン）)
4th Sounding Rocket Symposium(March 14-15, 2022. Hybrid(in-person & online) Conference (Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan
著者人数: 12名
資料番号: SA6000175010
レポート番号: Ⅱ-5

DOI： 10.1142/9789811260100_0074

Web of Science

Language：Others  

DOI： 10.5194/dach2022-84

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

DOI： 10.1029/2021SW002883

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

DOI： 10.1029/2021SW003000

Language：Others  

DOI： 10.5194/dach2022-81

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

DOI： 10.1029/2021SW002756

Language：Japanese  

第3回観測ロケットシンポジウム（2021年3月24-25日. オンライン開催)
3rd Sounding Rocket Symposium (March 24-25, 2021. Online Meeting)
著者人数: 12名
資料番号: SA6000162010
レポート番号: Ⅲ-3

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

DOI： 10.1029/2020SW002695

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

DOI： 10.1029/2020ja027789

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

Peer reviewing is the foundation of modern scholarship, with external specialists being asked to fairly check and evaluate submitted work. This difficult and often time-consuming activity is performed voluntarily, with the understanding that one's own scholarship shall benefit down the line from a careful analysis of its assumption, results, accuracy, and yes, language, as we are now evaluating someone else's work. At Space Weather, we pride ourselves on a fair but quick review process yielding high-quality articles with a time from submission to first decision of under one month. This would not be possible without the hard work of all our reviewers. Once a year, we take the occasion to name these women and men in order to thank them for their service to the journal and the community.

DOI： 10.1029/2020SW002481

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

Submillimeter-Wave Limb-Emission Sounder 2 (SMILES-2) is a satellite mission proposed in Japan to probe the middle and upper atmosphere (20-160 km). The main instrument is composed of 4K cooled radiometers operating near 0.7 and 2 THz. It could measure the diurnal changes of the horizontal wind above 30 km, temperature above 20 km, ground-state atomic oxygen above 90 km and atmospheric density near the mesopause, as well as abundance of about 15 chemical species. In this study we have conducted simulations to assess the wind, temperature and density retrieval performance in the mesosphere and lower thermosphere (60- 110 km) using the radiometer at 760 GHz. It contains lines of water vapor (H₂O), molecular oxygen (O2) and nitric oxide (NO) that are the strongest signals measured with SMILES-2 at these altitudes. The Zeeman effect on the O2 line due to the geomagnetic field (B) is considered; otherwise, the retrieval errors would be underestimated by a factor of 2 above 90 km. The optimal configuration for the radiometer's polarization is found to be vertical linear. Considering a retrieval vertical resolution of 2.5 km, the line-of-sight wind is retrieved with a precision of 2-5ms^-1 up to 90 km and 30ms^-1 at 110 km. Temperature and atmospheric density are retrieved with a precision better than 5K and 7% up to 90 km (30K and 20% at 110 km). Errors induced by uncertainties on the vector B are mitigated by retrieving it. The retrieval of B is described as a side-product of the mission. At high latitudes, precisions of 30-100 nT on the vertical component and 100-300 nT on the horizontal one could be obtained at 85 and 105 km (vertical resolution of 20 km). SMILES-2 could therefore provide the first measurements of B close to the electrojets' altitude, and the precision is enough to measure variations induced by solar storms in the auroral regions.

DOI： 10.5194/amt-13-219-2020

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

Submillimeter-Wave Limb-Emission Sounder 2 (SMILES-2) is a satellite mission proposed in Japan to probe the middle and upper atmosphere (20-160 km). The main instrument is composed of 4K cooled radiometers operating near 0.7 and 2 THz. It could measure the diurnal changes of the horizontal wind above 30 km, temperature above 20 km, ground-state atomic oxygen above 90 km and atmospheric density near the mesopause, as well as abundance of about 15 chemical species. In this study we have conducted simulations to assess the wind, temperature and density retrieval performance in the mesosphere and lower thermosphere (60-110 km) using the radiometer at 760 GHz. It contains lines of water vapor (H2O), molecular oxygen (O-2) and nitric oxide (NO) that are the strongest signals measured with SMILES-2 at these altitudes. The Zeeman effect on the O-2 line due to the geomagnetic field (B) is considered; otherwise, the retrieval errors would be underestimated by a factor of 2 above 90 km. The optimal configuration for the radiometer's polarization is found to be vertical linear. Considering a retrieval vertical resolution of 2.5 km, the line-of-sight wind is retrieved with a precision of 2-5 m s(-1) up to 90 km and 30 m s(-1) at 110 km. Temperature and atmospheric density are retrieved with a precision better than 5K and 7% up to 90 km (30K and 20% at 110 km). Errors induced by uncertainties on the vector B are mitigated by retrieving it. The retrieval of B is described as a side-product of the mission. At high latitudes, precisions of 30-100 nT on the vertical component and 100-300 nT on the horizontal one could be obtained at 85 and 105 km (vertical resolution of 20 km). SMILES-2 could therefore provide the first measurements of B close to the electrojets' altitude, and the precision is enough to measure variations induced by solar storms in the auroral regions.

DOI： 10.5194/amt-13-219-2020

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

DOI： 10.1186/s40623-019-1025-7

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

DOI： 10.1186/s40623-019-1070-2

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

In recent decades, significant efforts have been made to characterize and understand the global pattern of ionospheric long-term trend. However, little attention has been paid to the topside ionosphere trend. In this study, the unique in situ data measured by series Defense Meteorological Satellite Program (DMSP) satellites were utilized to derive the long-term trend of the topside ionosphere for the first time. We checked carefully data quality, gap, and consistency between different satellites for both electron density and ion temperature, and compared the techniques of artificial neuron network (ANN) and multiple linear regression methods for deriving the trend. The electron density (N_e) trend in the middle and low latitudes at ~860 km around 18 MLT was derived using the ANN method from 1995–2017. The trend from DMSP observations has a mean magnitude ranging from ~ − 2% to ~2% per decade, with clear seasonal, latitude and longitude variations. The derived trend was evaluated by directly comparing with the simulated trend at 500 km from the NCAR-TIEGCM driven by realistic changes of CO₂ level and geomagnetic field. The observed and simulated trends have similar geographic distribution patterns at 18 MLT. The good agreement between the observed trend around 860 km and the simulated trend near 500 km implies that the physical processes controlling the N_e trends above the peak height might be identical. Further control simulations show that the geomagnetic field secular variation is the dominant factor of the electron density trend at around 500 km, rather than the CO₂ long-term enhancement.

DOI： 10.1029/2019JA027522

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

DOI： 10.1186/s40623-019-1070-2

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

This study provides a climatological view of density cell structures at high latitudes in the lower thermosphere, using neutral mass density at 270 km derived from Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite. Three types of the density cells named isolated low, isolated high, and wavy density cells are analyzed. Our results revealed that the density cell structures generally occur in the Northern Hemisphere and the local summer, but they are less frequently observed in the Southern Hemisphere. The low density cell tends to have greater occurrence in the dawn side than in other sampled local times, while the high and wavy density cells occur more frequently in the morning side in terms of the GOCE trajectory. Moreover, the characteristics of density cell structures, including the central locations, horizontal scales, and relative magnitudes, strongly depend on the type of the density cell structure. These results can serve as a baseline to further validate the theoretical models and also to improve our understanding of the density variability of the lower thermosphere at high latitudes.

DOI： 10.1029/2019GL084951

Language：English  

DOI： 10.1186/s40623-019-1070-2

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

DOI： 10.1029/2019SW002194

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

©2019. American Geophysical Union. All Rights Reserved. Peer review remains one of the most important service activities for scientists. Through the time-consuming process of peer review, community volunteers set the bar for the quality of science that is shared with each other and with the world. Attentive, patient, and critical review is required to maintain rigorous and accurate scientific reporting. Reviewers donate their time and effort with little incentive outside of the knowledge that they are contributing to sustain scientific rigor. Space Weather is fortunate to be able to continually rely on our reviewers to maintain a journal that receives and publishes high-quality, high-impact articles. We recognize the time, effort, and dedication each review requires. For this, we extend a heartfelt thank you to all of our 2018 reviewers. We sincerely appreciate your choice to respond positively to our review requests. Last year, Space Weather received 785 peer reviews from 354 individuals. The reviewers who contributed three or more reviews are recognized in italics below. Thank you all for your contributions in 2018.

DOI： 10.1029/2019SW002194

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

We report the first comparison of ground and satellite measurements of low-latitude traveling ionospheric disturbances (TIDs). Three TID events were simultaneously observed by a 630.0-nm airglow imager and the CHAllenging Minisatellite Payload (CHAMP) satellite at Kototabang, Indonesia (geographic coordinates: 0.2 degrees S, 100.3 degrees E, geomagnetic latitude: 10.6 degrees S). In 630.0-nm airglow images of all three events, there are clear southward-moving structures. Events 1 and 2 are a single pulse with horizontal scales of similar to 500-1,000 km. Event 3 shows five wave fronts with a horizontal scale size of 500-1,000 km. All three TIDs are medium-scale TIDs. Horizontal wavelengths of both airglow intensity at an average emission altitude of 250 km and CHAMP neutral density variations measured at 400 km are estimated by fitting a sinusoidal function to the observed data. The estimated horizontal wavelengths for airglow and neutral density data are 1,031 and 880 km for event 1 and 560 and 420 km for event 3, respectively. These values between airglow and CHAMP are comparable, suggesting both instruments are observing the same wave. For event 1, the CHAMP electron density mapped along the geomagnetic field line onto the airglow altitude does not show wave structure similar to the airglow variation. For events 2 and 3, the plasma density did not show wavy structures similar to the waves seen in the airglow image and CHAMP neutral density. These results suggest that the TIDs observed in airglow images are not caused by ionospheric plasma instability but by gravity waves in the thermosphere.

DOI： 10.1029/2018JA025634

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

Precursor effect of March 11 2011 off the coast of Tohoku earthquake on high and low latitude ionospheres and its possible disturbing mechanism

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

DOI： 10.1186/s40623-018-0916-3

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

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.

DOI： 10.1029/2018GL077898

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

The current status of ionospheric precursor studies associated with large earthquakes (EQ) is summarized in this report. It is a joint endeavor of the “Ionosphere Precursor Study Task Group,” which was formed with the support of the Mitsubishi Foundation in 2014–2015. The group promotes the study of ionosphere precursors (IP) to EQs and aims to prepare for a future EQ dedicated satellite constellation, which is essential to obtain the global morphology of IPs and hence demonstrate whether the ionosphere can be used for short-term EQ predictions. Following a review of the recent IP studies, the problems and specific research areas that emerged from the one-year project are described. Planned or launched satellite missions dedicated (or suitable) for EQ studies are also mentioned.

DOI： 10.1186/s40562-016-0038-3

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

Alfvén waves have been proposed as an important mechanism for the heating of the Sun's outer atmosphere and the acceleration of solar wind, but they are generally believed to have no significant impact on the Earth's upper atmosphere under quiet geomagnetic conditions due to their highly fluctuating nature of interplanetary magnetic field (i.e., intermittent southward magnetic field component). Here we report that a long-duration outward propagating Alfvén wave train carried by a high-speed stream produced continuous (∼2 days) and strong (up to ±40%) density disturbances in the Earth's thermosphere in a way by exciting multiple large-scale gravity waves in auroral regions. The observed ability of Alfvén waves to excite large-scale gravity waves, together with their proved ubiquity in the solar atmosphere and solar wind, suggests that Alfvén waves could be an important solar-interplanetary driver of the global thermospheric disturbances.

DOI： 10.1038/srep18895

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

To investigate whether the link between seismic activity and EIA (equatorial ionization anomaly) enhancement is valid for mid-latitude seismic activity, DEMETER observations around seven large earthquakes in the north-east Asian region were fully analyzed (M⩾6.8). In addition, statistical analysis was performed for 35 large earthquakes (M⩾6.0) that occurred during the DEMETER observation period. The results suggest that mid-latitude earthquakes do contribute to EIA enhancement, represented as normalized equatorial N _e , and that ionospheric change precedes seismic events, as has been reported in previous studies. According to statistical studies, the normalized equatorial density enhancement is sensitive and proportional to both the magnitude and the hypocenter depth of an earthquake. The mechanisms that can explain the contribution of mid-latitude seismic activity to EIA variation are briefly discussed based on current explanations of the geochemical and ionospheric processes involved in lithosphere–ionosphere interaction.

DOI： 10.1016/j.asr.2015.08.030

Language：English  

In this study, we constructed an empirical model of the equatorial electrojet (EEJ), including local time and longitudinal dependence, based on simultaneous data from 12 magnetometer stations located in six longitude sectors. An analysis was carried out using the equatorial electrojet index, EUEL, calculated from the geomagnetic northward H component. The magnetic EEJ strength is calculated as the difference between the normalized EUEL index of the magnetic dip equator station and the normalized EUEL index of the off-dip equator station located beyond the EEJ band. Analysis showed that this current is always strongest in the South American sector, regardless of local time (LT), and weakest in the Indian sector during 0900 and 1000 LT, but shifted to the African sector during 1100 to 1400 LT. These longitude variations of EEJ roughly follow variations of the inversed main field strength along the dip equator, except for the Indian and Southeast Asian sectors. The result showed that the EEJ component derived from the model exhibits a similar pattern with measured EEJ from ground data during noontime, mainly before 1300 LT.

DOI： 10.1186/s40623-015-0373-1

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

In the E layer of equatorial ionosphere, the equatorial electrojet (EEJ) current interacts with the global Sq current and caused abnormally large amplitude of geomagnetic field component measured at the magnetic dip equator station. In this study, we attempted to separate EEJ and Sq at dip equator using the EUEL index derived from MAGDAS/CPMN stations. Moreover, we normalized the observation data to overcome the uncertainties due to the latitudinal variation of both EEJ and Sq currents which are neglected in most of previous studies. This new approach allowed the study of longitudinal dependence of EEJ. Analysis is performed using data from stations at East and West of Southeast Asian sector for a year of 2011. Additionally, we examined the solar activity dependence of EEJ during this inclining phase of solar cycle.

DOI： 10.1109/IconSpace.2015.7283763

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

Exogenous parameter is basically referred to the external activities that may have been the important factors in modulating the atmosphere, ionosphere and the earth's surface. Due to its significant impacts, there is possibility to link solar activities and seismicity. Associated investigations have been done by previous researchers in order to explore the solar - terrestrial connection; nevertheless, the physical mechanism is still controversial. To comprehend the investigation of this coupling mechanism, we propose another exogenous source to be analyzed which is cosmic ray. As solar activity, cosmic ray also has minimum and maximum phases or called as cosmic ray cycle, but it is anti-correlation between phases of sunspot and cosmic ray cycles. In this brief report, we examine the trend of shallow earthquake occurrence as the caused effect during recent 4 complete solar cycles (SC 20-23) in order to study its possible link to sun spot number (SSN). The earthquakes were categorized into very shallow earthquakes with epicenter depth less than 35 km and deeper earthquakes with epicenter depth between 35-70 km. For very shallow earthquakes, the analysis shows two interesting features. First, its occurrence rate shows a steady increase during the 40 years period of 1964-2005, with average increase rate about 150/year. Second, a distinct increase of the occurrence rate occurs during each solar minimum of SC 21-23. Neither of these features is found in the earthquakes with deeper epicenters, suggesting that the solar influence on seismicity, if exists, is likely to exist only in the case of very shallow earthquakes whose epicenter is in the crust region.

DOI： 10.1109/RAST.2015.7208401

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

The Weddell Sea Anomaly (WSA) is a recurrent feature of the austral summer midlatitude ionosphere where electron densities are observed to maximize during the local nighttime. In this study, tidal decomposition is applied to FORMOSAT-3 (Formosa Satellite)/Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) total electron content (TEC) and electron density observations between 2007 and 2012 to quantify the components dominating local time and spatial variation in the WSA region. Our results present some of the first three-dimensional spaceborne analyses of the WSA from a tidal perspective over multiple years. We find that the features of the WSA can be reconstructed as the result of superposition between the dominant diurnal standing (D0), eastward wave number 1 (DE1), westward wave number 2 (DW2), and stationary planetary wave 1 (SPW1) components in TECs, producing the characteristic midnight WSA peak. The D0, DE1, DW2, and SPW1 components are found to be an interannually recurring feature of the southern midlatitude to high-latitude ionosphere during the summer, manifesting as enhancements in electron density around 300km altitude of the summer middle to high magnetic latitudes. The phases of the aforementioned nonmigrating diurnal signatures in electron density in this region are near evanescent, suggesting in situ generation, rather than upward propagation from below. However, the SPW1 signature shows some signs of an eastward tilt with altitude, suggesting possible downward propagation. The relation of these components to possible generation via in situ photoionization or plasma transport along magnetic field lines is also discussed using results from the Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy (GAIA) general circulation model (GCM), connecting the tidal interpretation of the WSA to previously examined generation mechanisms.

DOI： 10.1002/2014JA020752

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

This paper presents a two-dimensional structure of the shock wave signatures in ionospheric electron density resulting from a rocket transit using the rate of change of the total electron content (TEC) derived from ground-based GPS receivers around Japan and Taiwan for the first time. From the TEC maps constructed for the 2009 North Korea (NK) Taepodong-2 and 2013 South Korea (SK) Korea Space Launch Vehicle-II (KSLV-II) rocket launches, features of the V-shaped shock wave fronts in TEC perturbations are prominently seen. These fronts, with periods of 100-600 s, produced by the propulsive blasts of the rockets appear immediately and then propagate perpendicularly outward from the rocket trajectory with supersonic velocities between 800-1200 ms(-1) for both events. Additionally, clear rocket exhaust depletions of TECs are seen along the trajectory and are deflected by the background thermospheric neutral wind. Twenty minutes after the rocket transits, delayed electron density perturbation waves propagating along the bow wave direction appear with phase velocities of 800-1200 ms(-1). According to their propagation character, these delayed waves may be generated by rocket exhaust plumes at earlier rocket locations at lower altitudes.

DOI： 10.5194/angeo-32-1145-2014

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

In this paper we report the detection of full constructive interference between two large-scale gravity waves in the upper thermosphere from the CHAMP accelerometer measurements. The two waves are separately excited in northern and southern auroral regions by the shock-induced auroral intensification on 29 October 2003. They propagate equatorward and encounter near the equator, where constructive interference occurs and causes nightside equatorial neutral density enhancements of similar to 60%. This result demonstrates that the constructive interference can be a potential mechanism for large density increases in the equatorial region during magnetically active periods.

DOI： 10.1002/2014JA020255

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

Changes of the zonal mean state of the thermosphere during the 2009 stratospheric sudden warming (SSW) have been investigated using the Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy (GAIA) model. Both the zonal mean thermal and dynamical structure of the thermosphere exhibit pronounced changes during the SSW in terms of zonal mean temperature and winds. First, the zonal mean temperature above 100 km altitude drops at all latitudes except for in a narrow band around 60 degrees N. Such temperature perturbations are found to be dominantly caused by changes in direct heating/cooling processes related to solar radiation and thermal heat conduction at high latitudes, but by dynamical processes in tropical regions. Second, the zonal mean zonal wind experiences a strong westward perturbation in the tropical thermosphere, along with distinct change in the meridional circulation. This change consists of two parts. One is a global scale north-to-south flow accompanied with upwelling/downwelling in the northern/southern polar region, the other is a fountain-like flow in tropical lower thermosphere. The large enhancement of semidiurnal tides is suggested to be the primary cause for the fountain-like flow.

DOI： 10.1002/2014JA020222

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

Total eastward and westward electrojet currents (EEJ and WEJ) and their central latitudes derived from the International Monitor for Auroral Geomagnetic Effects (IMAGE) network magnetic measurements are analyzed for the combined MLT (magnetic local time) and seasonal dependence during the period 1995-2009. EEJ shows a strong MLT variation with significant dependence on season. During summer months the maxima occur around 1600-1800 MLT, whereas during winter months the maxima occur around 1800-2000 MLT. Moreover, the summer maxima are much larger than the winter maxima and appear at higher latitudes. The summer maxima are mainly associated with the solar EUV conductivity effect, while the winter maxima are mainly due to the contribution of northward convective electric field. EEJ exhibits a dominant annual variation with maximum in summer and minimum in winter. WEJ also exhibits a strong MLT variation with significant dependence on season. The maxima occur around 0200-0400 MLT during summer months, around 0000-0200 MLT during winter months, and around 0000-0400 MLT during equinoctial months. Moreover, the equinoctial maxima are much larger than the summer and winter maxima and appear at relatively lower latitudes. The seasonal variations in WEJ are the combinations of annual variations and semiannual variations. Both annual and semiannual variations show significant dependence on MLT. These results increase our knowledge on what factors contribute to the auroral electrojets as well as their magnetic signatures and hence help us better understand the limitations of global auroral electrojet indices, such as the AE and SME indices.

DOI： 10.1002/2014JA019843

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

The International Monitor for Auroral Geomagnetic Effects network magnetic measurements during the period 1995-2009 are used to characterize the annual variations in the westward electrojet. The results suggest that the annual variations in different local time sectors are quite different due to the different sources. In the MLT sector 2200-0100, the annual variations with maxima in winter suggest they are caused by the combined effects of the convective electric field and the conductivity associated with particle precipitation. Furthermore, the conductivity seems to play a more important role in the MLT sector similar to 2200-2320, while the convective electric field appears to be more important in the MLT sector similar to 2320-0100. In the MLT sector 0300-0600, the annual variations with maxima in summer suggest they are caused by solar EUV conductivity effect and the equinoctial effect. The solar EUV conductivity effect works by increasing ionospheric conductivity and enhancing the westward electrojet in summer, while the equinoctial effect works by decreasing solar wind-magnetosphere coupling efficiency and weakening the westward electrojet in winter. In the MLT sector 0100-0300, the annual variations are relatively weak and can be attributed to the combined effects of annual variations caused by all the previously mentioned effects. In addition, we find that a significant annual variation in substorm occurrence rate, mainly occurring in the premidnight region, is quite similar to that in the westward electrojet. We suggest that elevated solar wind driving during the winter months contributes to higher substorm occurrence in winter in the Northern Hemisphere.

DOI： 10.1002/2013JA019742

Language：Japanese  

The Importance of Plasma-Neutral Coupling in Understanding Ionospheric Disturbances

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

A one-dimensional kinetic model is constructed to simulate the electron acceleration by inertial Alfven waves. The electrons are divided into cold and hot electrons and treated separately. Cold components are described by the fluid equation and hot ones by the Vlasov equation, both carrying field-aligned currents. Intense variation of Alfven speed has been introduced by inclusion of cold electrons. The model results show that the exponential decrease of the plasma density plays a key role, which leads to the sharp gradient of both Alfven velocity and electron inertial length. When Alfven waves encounter this sharp gradient at lower altitudes, the electrons accelerated by the waves become super-Alfvenic, and the width of burst structures becomes much wider than the electron inertial length. Consequently, the background electrons carry the oppositely field-aligned current due to plasma oscillation. It is demonstrated that the current carried by the electrons exceeding the wavefront is balanced by the reverse current carried by background electrons. This mechanism can be used to reasonably explain observations of the electron bursts accompanied by little net field-aligned current. Furthermore, our simulation indicates another type of Alfven wave reflection due to mirror force and wave-particle interaction.

DOI： 10.1002/jgra.50355

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

The decadal observations from CHAMP satellite have provided ample information on the Earth's upper thermosphere, reshaping our understandings of the vertical coupling in the atmosphere and near-Earth space. An empirical model of the thermospheric mass density is constructed from these high-resolution observations using the multivariable least-squares fitting method. It describes the density variation with latitude, longitude, height, local time, season, and solar and geomagnetic activity levels within the altitude range of 350-420 km. It represents well prominent thermosphere structures like the equatorial mass density anomaly (EMA) and the wave-4 longitudinal pattern. Furthermore, the empirical model reveals two distinct features. First, the EMA is found to have a clear altitude dependence, with its crests moving equatorward with increasing altitude. Second, the equinoctial asymmetry is found to strongly depend on solar cycle, with its magnitude and phase being strongly regulated by solar activity levels. The equinoctial density maxima occur significantly after the actual equinox dates toward solar minimum, which may signal growing influence from the lower atmosphere forcing. This empirical model provides an instructive tool in exploring thermospheric density structures and dynamics. It can also be easily incorporated into other models to have a more accurate description of the background thermosphere, for both scientific and practical purposes. Citation: Liu, H., T. Hirano, and S. Watanabe (2013), Empirical model of the thermospheric mass density based on CHAMP satellite observation, J. Geophys. Res. Space Physics, 118, 843-848, doi: 10.1002/jgra.50144.

DOI： 10.1002/jgra.50144

Language：Others  

Electromagnetic coupling on solar-terrestrial system: Possible effects on seismic activities
Solar wind parameters play significant roles in electromagnetic coupling of the Sun - Earth system. By having a long period of observation and analysis of solar activities and its influence on geomagnetic or seismic activities, it is possible to reveal the interconnection between them. In the present paper, we analyzed the earthquake (EQ) events as seismic parameters, which extracted from Advanced National Seismic System (ANSS) database. The different earthquake magnitudes were analyzed with the solar parameters; high-speed solar wind (HSSW) events, and solar wind dynamic pressure (SW Pdyn). All of these analyses were done from year 1964 to 2008, which covers the latest entire solar cycles (cycle number 20 to 23). In the analysis, we propose how the electromagnetic energy can be transferred from the solar wind to the lower ionosphere and finally affected the geomagnetic activities by showing the plots and the statistical analysis on plasma speed event (Vsw), solar wind dynamic pressure (SW Pdyn), solar wind input energy and ring current (Dst) index. The analyzed results show a significant relationship between solar and terrestrial parameters. © 2012 IEICE.

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

Ionospheric Sq current systems during unusually strong and prolonged stratospheric sudden warming (SSW) events in January 2006 and January 2009 are examined by analyzing ground-magnetometer data for the American and Asian longitude sectors. During these SSW events, a significant decrease and increase of the Sq equivalent current intensity are observed in the Northern and Southern Hemispheres, respectively, along with a reduction in the longitudinal separation between the northern and southern current vortices. Numerical experiments using the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General-Circulation Model show that changes in the solar anti-symmetric (2,3) semidiurnal tide can bring about similar changes in the Sq current system. Citation: Yamazaki, Y., A. D. Richmond, H. Liu, K. Yumoto, and Y. Tanaka (2012), Sq current system during stratospheric sudden warming events in 2006 and 2009, J. Geophys. Res., 117, A12313, doi:10.1029/2012JA018116.

DOI： 10.1029/2012JA018116

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

The strong westward electrojet and simultaneous upward drift of the equatorial ionospheric peak observed over South-East Asia and Indian equatorial regions during the prolonged Dst minimum phase of an intense geomagnetic storm during 14-15 December 2006 are investigated for the altitudinal variation of zonal electric field polarity using ground based and space-borne observations. The results show first observational evidence for simultaneous existence of daytime westward and eastward zonal electric fields at equatorial E and F region altitudes, respectively, in a wide longitude sector. While the westward electric fields at E region altitudes cause westward electrojet, at the same time, the eastward zonal electric fields at F region altitudes cause the upward drift of the equatorial ionospheric peak and reinforcement of the equatorial ionization anomaly (EIA) even in the topside ionosphere (similar to 660 km). The reversal of the electric fields is found to occur at similar to 280 km height. A clear bifurcation of F region plasma at similar to 280 km is evident in the iso-electron density contours due to these oppositely polarized zonal electric fields, which manifests as an unusually deep cusp between F-1 and F-2 layers on equatorial ionograms. Citation: Tulasi Ram, S., N. Balan, B. Veenadhari, S. Gurubaran, S. Ravindran, T. Tsugawa, H. Liu, K. Niranjan, and T. Nagatsuma (2012), First observational evidence for opposite zonal electric fields in equatorial E and F region altitudes during a geomagnetic storm period, J. Geophys. Res., 117, A09318, doi:10.1029/2012JA018045.

DOI： 10.1029/2012JA018045

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

We have examined excitation mechanism of the fast jet of the neutral atmosphere along the dip equator in the upper thermosphere. The zonal momentum balance of the neutral atmosphere is estimated using an atmosphere-ionosphere coupled model. The coupled model used in this study is a self-consistent global model of the atmosphere and ionosphere covering the height range from the ground surface to the exobase. It can reproduce the observed equatorial fast jet above 250 km heights. The analysis of the zonal momentum balance reveals that the pressure gradient and ion drag play an important role on the formation of the fast jet near the dip equator. In particular, the fast jet near the equator is closely related with the latitudinal difference of the ion drag force. We also investigate the zonal momentum balance of the longitudinal wave-4 structure of the zonal wind in the fixed local time frame. Furthermore, significant day-to-day variations in the neutral zonal wind and the ion drift near the dip equator are obtained although the solar UV/EUV fluxes and the energy input from the magnetosphere are assumed to be constant during the numerical simulation. This result indicates the importance of the lower atmospheric variability on day-to-day variations in the thermosphere/ionosphere.

DOI： 10.1029/2011JA017373

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

Using ground observations of total electron content (TEC) and equatorial electrojet (EEJ) in the Asian sector, along with plasma and neutral densities obtained from the CHAMP satellite, we investigate the ionospheric electrodynamics and neutral background in this longitude sector during the major stratospheric sudden warming (SSW) in January 2009. Our analysis reveals the following prominent features. First, the TEC response in tropical regions is strongly latitude dependent, with monotonic depletion at the dip equator but a semidiurnal perturbation at low latitudes. Second, the TEC semidiurnal perturbation possesses a significant hemispheric asymmetry in terms of onset date and magnitude. It starts on the same day as the SSW peak in the Northern Hemisphere but 2 days later in the Southern Hemisphere. Its magnitude is twice as strong in the north than in the south. Third, strong counter electrojet occurs in the afternoon, following the strengthening of the eastward EEJ in the morning. Fourth, semidiurnal perturbation in both TEC and EEJ possesses a phase shift, at a rate of about 0.7 h/day. Comparisons with results reported in the Peruvian sector reveal clear longitude dependence in the amplitude and hemispheric asymmetry of the semidiurnal perturbation. Finally, thermospheric density undergoes similar to 25% decrease at low latitudes in the afternoon local time sector during the SSW, indicating significant cooling effects in the tropical upper thermosphere.

DOI： 10.1029/2011JA016607

Language：English  

Sreeja et al. [2011] have claimed that the "geomagnetic storm that occurred during the period from 21 to 25 July 2009 is anomalous because the storm main phase developed during northward interplanetary magnetic field (IMF)" and "westward electric field penetration to the day-side equatorial ionosphere during the main phase of the storm." However, as discussed subsequently, the so-called "anomalous" feature of geomagnetic storm is ill-fully claimed due to their incorrect IMF B(z) data. Since Sreeja et al. [2011] have made serious claims such as the geomagnetic storm of 21-25 July 2009 is anomalous which would have adverse impact on the future scientific investigations, it is highly necessary to clarify.

DOI： 10.1029/2011JA016634

Language：English  

On the formation of a fast thermospheric zonal wind at the magnetic dip equator

DOI： 10.1029/2011GL047255

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

The Imager for Sprites and Upper Atmospheric Lightning (ISUAL) payload on board the FORMOSAT-2 satellite carried out the first limb imaging observation of 630 nm airglow for the purpose of studying physical processes in the F region ionosphere. For a total of 14 nights in 2006-2008, ISUAL scanned the midnight latitude-altitude distribution of 630 nm airglow in the Asian sector. On two nights of relatively active conditions (Sigma Kp = 26, 30+) we found several bright airglow regions, which were highly variable each night in terms of luminosity and location. In relatively quiet conditions (Sigma Kp = 4-20) near May/June we found two bright regions which were stably located in the midlatitude region of 40 degrees S-10 degrees S (50 degrees S-20 degrees S magnetic latitude (MLAT)) and in the equatorial region of 0 degrees-10 degrees N (10 degrees S-0 degrees MLAT). On one of the quiet nights, FORMOSAT-3/COSMIC and CHAMP simultaneously measured the plasma density in the same region where ISUAL observed airglow. The plasma density data generally show good agreement, suggesting that plasma enhancements were the primary source of these two bright airglow regions. From detailed comparison with past studies we explain that the airglow in the equatorial region was due to the midnight brightness wave produced in association with the midnight temperature maximum, while that in the midlatitude region was due to the typical plasma distribution usually formed in the midnight sector. The fact that the equatorial airglow was much brighter than the midlatitude airglow and was observed on most nights during the campaign period strongly suggests the importance of further studies on the MTM/MBW phenomenology, which is not well reproduced in the current general circulation model.

DOI： 10.1029/2009JA015147

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

The first observations of solar eclipse induced mid-latitude plasma irregularities using the middle and upper atmosphere radar (MU radar) at Shigaraki (34.85 degrees N, 136.1 degrees E, 25.0 degrees N geomagnetic) are presented. The observations were done during the partial solar eclipse on 22 July, 2009. The observations show that the sudden withdrawal of solar radiation could deplete the background E-region densities, thereby unmasking the long-lived metallic ions within the strong and patchy Sporadic E-layers. As a result of this, Quasi-Periodic (QP) echoes were generated, which were detected by the MU radar. These echoes resemble the normal post-sunset QP echoes observed over mid-latitudes as revealed by the multi-channel interfereometry imaging. This example shows that over mid-latitudes E-region plasma irregularities can be generated during a partial solar eclipse, revealing a hitherto unobserved aspect of mid-latitude ionospheric responses to eclipses. Citation: Thampi, S. V., M. Yamamoto, H. Liu, S. Saito, Y. Otsuka, and A. K. Patra (2010), Nighttime-like quasi periodic echoes induced by a partial solar eclipse, Geophys. Res. Lett., 37, L09107, doi: 10.1029/2010GL042855.

DOI： 10.1029/2010GL042855

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

The typical diurnal cycle of the midlatitude F region electron density consists of a midday maximum and a midnight minimum. However, a phase reversal of this diurnal cycle has been found to occur in three distinct regions on the globe. They are the East Asian (EA) region centered around (53 degrees N, 150 degrees E), the Northern Atlantic (NA) region centered around (45 degrees N, 50 degrees W) and the South Pacific (SP) region centered around (60 S, 110 degrees W). The intensively reported Weddell Sea Anomaly falls inside the SP region. The phase reversal occurs during March-August in EA and NA regions, and between August and March in SP region, being most prominent in local summer. Furthermore, this diurnal anomaly is more pronounced at solar minimum than at solar maximum, and more pronounced in SP region than in NA and EA regions, in terms of larger diurnal magnitude and more months it lasts in a year. It is emphasized that the diurnal anomaly consists of not only a nighttime enhancement, but also a concurrent noontime depletion. Hence, midlatitude summer nighttime enhancements reported in previous studies are just part of this reversed diurnal cycle. The cause for the phase reversal involves several interplaying physical processes. Among these, the neutral wind combined with the geomagnetic field configuration plays a pivotal role. It generates a one-wave longitudinal pattern at southern middle latitudes and a two-wave pattern at northern middle latitudes, whose wave peaks correspond to the center of the SP, EA, and NA regions, respectively. The seasonal variation of neutral winds and downward motion of the ionization induced by thermal contraction of the ionosphere at sunset may largely control the occurring local time of the nighttime density enhancement and how long it persists in different months. The phase reversal occurs as a result of close ion-neutral coupling. It is further noted that winter anomaly in the EA, NA, and SP regions is very weak or missing.

DOI： 10.1029/2009JA014689

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

Recently, a chain of digital beacon receivers has been established over Japan, mainly for the tomographic imaging of the ionosphere. These receivers are installed at Shionomisaki (33.45 degrees N, 135.8 degrees E), Shigaraki (34.85 degrees N, 136.1 degrees E), and Fukui (36.06 degrees N, 136 degrees E), which continuously track the Low Earth Orbiting Satellites (LEOS), and the simultaneous line-of-sight Total Electron Content (TEC) data are used for tomographic reconstruction. In the images obtained during July 2008, it is seen that the nighttime electron densities exceed the daytime values on almost all days over latitudes > 33-34 degrees N. On several days, these northern latitudes show enhanced electron densities compared to the low-latitude region during nighttime. These are the prominent features of the "Midlatitude Summer Nighttime Anomaly (MSNA)'' that is recently observed in the northern hemisphere and is considered similar to the nighttime Weddell Sea Anomaly (WSA). This is the first study of the MSNA using tomographic technique and found its significant day-to-day variability. The ionosonde data from Wakkanai (45.4 degrees N, 141.7 degrees E), ground-based GPS TEC observations using the GEONET, CHAMP in situ electron density measurements, and Formosat3/COSMIC (F3/C) occultation measurements are also used to confirm the presence of MSNA over this region and to examine its variability. It is seen that, in general, during the local summer period, electron density over the northern latitudes is highest at similar to 2000-2100 LT and the latitudinal enhancement in electron density also begins to appear around the same time, which continues to exist even at later hours.

DOI： 10.1029/2009JA014439

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

We have examined the longitudinal structure of the equatorial ionosphere at 400-km altitude in the noon and postsunset local time sectors in different seasons using 6 years of F-region plasma density observations from the CHAMP satellite. A four-peak wave structure is observed in both local time sectors. In the noon sector at a fixed solar flux level, this structure is observed to be most prominent around September equinox and weakest around December solstice. This seasonal dependence agrees well with that of the nonmigrating diurnal tides DE3, hence supporting a close coupling between the ionosphere and the mesosphere-lower thermosphere possibly via the DE3 tidal modulation of the E-layer dynamo. In the postsunset sector, however, such agreement cannot be claimed. In this sector, although the four-peak structure can be observed in all seasons at moderate and high solar flux levels, its seasonal dependence does not follow that of the DE3 tides. This structure becomes indiscernible near solstices at low solar flux levels. Furthermore, the postsunset four-peak wave structure exhibits larger amplitude than that during daytime, hence indicating that it is more likely an amplified feature rather than a remnant of the daytime structure. The prereversal enhancement is speculated to be a possible candidate to cause this amplification.

DOI： 10.1029/2008JA013027

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

We have investigated the solar activity dependence of the electron density at equatorial and low latitudes using 6 years ( a) of measurements between 1 August 2000 and 1 August 2006 from CHAMP and compared it with the international reference ionosphere ( IRI) model. The solar activity dependence observed by CHAMP at 400 km altitude exhibits significant variation with latitude, season, and local time. First, the electron density in the crest regions of the equatorial ionization anomaly ( EIA) grows roughly linearly from solar minimum to solar maximum, with a higher growth rate than that in the EIA trough region. Second, the solar activity dependence in the EIA crest regions varies strongly with season. The growth rate of the electron density with increasing solar activity around equinoxes is about 1.5 to 2 times greater than that near solstices. Third, the solar activity dependence of the EIA structure varies significantly with local time. In the noon sector the crest-to-trough ratio ( CTR) obtained at 400 km altitude varies within only a small range between 1.14 and 1.43 from solar minimum to solar maximum. In the postsunset local time sector, however, the CTR grows remarkably with solar activity level, reaching values of above 3.9 at solar maximum. These differences are attributed to the different solar activity dependence of the vertical plasma drift in corresponding local time sectors. The IRI model was found to reproduce the equatorial electron density well near 400 km in the noon sector at all solar activity levels. However, it significantly overestimates it in the postsunset to premidnight sector at high solar activity levels. The major cause for this overestimation has been found to be the IRI's inadequate representation of the F-2 layer maximum height ( h(m)F(2)) in this sector, while the IRI's lack of equatorial spread F seems to play only a minor role.

DOI： 10.1029/2007JA012616

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

[1] We examined the thermospheric and ionospheric responses to the solar flare on 28 October 2003, utilizing simultaneous observations of the electron and neutral density from the CHAMP satellite. Rapid thermospheric response within a few minutes was observed. In addition, the neutral and plasma perturbations contrasted each other remarkably. First, their temporal development differed. Though started nearly simultaneously, the plasma perturbation developed much faster and to a larger amplitude than its neutral counterpart. Second, their latitudinal distributions differed. At the initial stage of the response, the neutral density was enhanced by 20% almost homogeneously at all latitudes below 50 degrees N/S. In comparison, the plasma disturbance exhibited a distinctive latitudinal structure, with largest density enhancements of 68% at the dip equator, moderate increase of similar to 20% at midlatitudes, and depression up to 35% around 15 degrees N/S. This suggests a decoupling between the neutral and plasma disturbances during this stage. The plasma-neutral coupling via ion drag was found to become important about 2 - 3 hours after the flare bursts. Another interesting feature is that the equatorial ionization anomaly was significantly weakened during the flare. The observations demonstrated that electrodynamics related to the equatorial fountain dominated the photochemistry in controlling the flare-induced plasma density disturbances on 28 October 2003. This differs considerably from the nearly linear cos(SZA) dependence of flare-induced total electron content enhancements.

DOI： 10.1029/2007JA012313

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

The equatorial anomaly is an interesting and important feature of the Earth's thermosphere-ionosphere coupling in tropical regions. It is an anomalous latitudinal distribution found in both the ionized and unionized part of the atmosphere. Its equinox configuration consists of a minimum near the dip equator flanked by two maxima on both sides. The ionospheric side of this anomaly, often referred to as the equatorial ionization anomaly ( EIA), has long been recognized since the 1930s. However, its thermospheric counterpart was only to be glimpsed by the Dynamic Explorer 2 satellite in the 1970s. A global picture of it has been rather recently revealed by the CHAMP satellite in 2005. In this paper we complement previous studies by investigating the climatology of the equatorial mass anomaly ( EMA) in the thermosphere using 4 years of CHAMP measurements. Our analysis has revealed strong variation of the EMA with season and solar flux level. The EMA structure is most prominent around equinox, with a crest-to-trough ratio about 1.05 for F10.7 = 150. Near solstices, it is asymmetric about the dip equator. The density crest attains maximum 1-2 hours earlier and reaches higher values in the summer hemisphere than in the winter hemisphere. The density in EMA regions varies semiannually, with maxima near equinoxes. The latitudinal locations of the EMA crests undergo a seasonal variation, obviously following the movement of the subsolar point. The EMA structure has also been found to become more pronounced at higher solar flux levels. Both the location and magnitude of the EMA crests closely follow those of the EIA in corresponding seasons and solar flux levels, hence demonstrating strong plasma-neutral interaction. Furthermore, two seasonal asymmetries clearly present in the globally averaged density, with the density in March/December being similar to 15-20% higher than that in September/June.

DOI： 10.1029/2006JA012199

Language：Japanese  

Ion upflow observed in the polar ionospbere

DOI： 10.14943/gbhu.70.13

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

[ 1] Using 3 years ( 2002 - 2004), over 16,400 orbits of measurements from the accelerometer on board the CHAMP satellite, we have studied the climatology of the equatorial zonal wind in the upper thermosphere. Several main features are noticed. The most prominent one is that the solar flux significantly influences both the daytime and nighttime winds. It overrides the geomagnetic activity effect, which is found to be rather limited to the nightside. An elevation of the solar flux level from F10.7 approximate to 100 x 10(-22) W m(-2) Hz(-1) to F10.7 approximate to 190 x 10(-22) Wm(-2) Hz(-1) produces an eastward disturbance wind up to similar to 110 m s(-1). This consequently enhances the nighttime eastward wind but suppresses the daytime westward wind. A seasonal variation with weaker wind ( by over 50 m s(-1) at night) around June solstice than in other seasons has been observed regardless of solar flux and geomagnetic activity levels. The zonal wind is eastward throughout the night except around June solstice, where it ebbs to almost zero or turns even westward in the postmidnight sector at low solar flux level. The daytime wind is found to be generally more stable than the nighttime wind, particularly unresponsive to geomagnetic activities. Predictions from the Horizontal Wind Model find good agreement with the CHAMP-observed wind at high solar flux levels during nighttime. At low solar flux levels, however, the model strongly underestimates the westward wind during morning hours by 50 - 120 m s(-1) depending on season. The major difference between the HWM-predicted and the CHAMP-observed wind is seen in the phase of its diurnal variation. The CHAMP-observed wind turns eastward around 1200 - 1300 MLT instead of 1600 - 1700 MLT predicted by the model. Comparisons with ground FPI observations and the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) predictions show that the solar flux effect obtained from CHAMP is consistent with that modeled by TIEGCM. The solar flux dependence of zonal wind found here together with that of the zonal ion drift found in previous studies reflect the relative importance of the E- and F-region wind dynamo in the thermosphere-ionosphere coupling process. Furthermore, these wind measurements indicate that the Earth's atmosphere superrotates. The average superrotation speed amounts to about 22 m s(-1) for a solar flux level of F10.7 approximate to 100 x 10(-22) W m(-2) Hz(-1) but increases to 63 m s(-1) for F10.7 approximate to 190 x 10(-22) W m(-2) Hz(-1). Finally, the wind behavior presented in this study is longitudinally averaged and may differ from wind measurements at a certain longitude.

DOI： 10.1029/2005JA011415

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

With coordinated EISCAT and ESR radar data, ionospheric storm in both the dayside polar cap and the auroral oval during the major magnetic storm of May 15, 1997 is studied, focusing on the F-region negative storm. It is found that in both the polar cap and the auroral zone a F1-like peak of ionization appeared at 190km height during the main and recovery phases of the storm; while the normal F2 peak disappeared and great depletions of electron density occurred. In contrast, variations of ion temperature are very different in the two regions, with little change in polar cap while strong enhancement in auroral oval, implying a difference in key mechanisms for the negative storms in the two regions. The increase of O+ ion loss rate through chemical reaction due to Joule heating and enhancement of ion temperature resulted from strong electric field played a crucial role in the auroral zone. The plasma transport process, however, especially the long-lasting large ion upflow, is of great importance-in the polar cap. In addition, large F-region electron density depletion associated with null Joule heating and ion temperature enhancement is observed by EISCAT radar in the transient region of the two cells of plasma convection, which is caused by strong field-aligned O+ ion outflow when the radar passing through probably under the polar cleft ion fountain region.

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

An abnormal anti-sunward intense flow of plasma convection is observed by EISCAT radar in the high-latitude ionosphere near the polar cap boundary. It occurred at morning sector of MLT under conditions of southward IMF B-z during the recovery phase of a moderate magnetic storm. A synthetic analysis of radar data and in-situ satellite observations is made in combination with a tracing of magnetic field lines by means of magnetospheric field model on this event. It is evidently indicated that the abnormal reversed westward flow of plasma convection and the features of the plasma structure and property are probably the ionospheric signatures of magnetic reconnection taking place at the dayside magnetopause.

Language：English   Book type：Scholarly book

Event date： 2024.7

Language：English   Presentation type：Oral presentation (invited, special)  

Country：Korea, Republic of  

Atmosphere-Ionosphere Coupling and Its role in Space Weather

Event date： 2023.6

Language：Others   Presentation type：Oral presentation (general)  

Country：Other  

DW1 tidal enhancements in the equatorial MLT during 2015 El Nino: the relative role of tidal heating and propagation

Event date： 2023.5

Language：Others  

Country：Other  

DW1 tidal enhancements in the equatorial MLT during 2015 El Nino: the relative role of tidal heating and propagation

Event date： 2023.5

Language：Others  

Country：Other  

DW1 tidal enhancements in the equatorial MLT during 2015 El Nino: the relative role of tidal heating and propagation

Event date： 2022.7

Language：English  

Country：Other  

Atmosphere-Ionosphere Coupling and Its role in Space Weather

Event date： 2022.2

Language：English  

Country：Other  

DW1 enhancement in MLT during 2015 El Niño

Event date： 2021.8

Language：English   Presentation type：Oral presentation (general)  

Country：Other  

How does geomagnetic activity affect the CO2-driven trend in the thermosphere and ionosphere

Event date： 2021.8

Language：English  

Country：Other  

How does geomagnetic activity affect the CO2-driven trend in the thermosphere and ionosphere

Event date： 2021.5 - 2021.6

Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Online   Country：Germany  

Event date： 2021.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：Austria  

Event date： 2021.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：Austria  

Event date： 2021.1 - 2021.2

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：Australia  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：Online   Country：Japan  

Event date： 2020.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2020.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2020.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Thermosphere cooling is a known effect of increasing CO2 in the atmosphere. In this study, we explore the changes of thermosphere circulation and tides in the cooled thermosphere via a doubled CO2 numerical experiment using the Ground-to-topside Atmosphere Ionosphere model for Aeronomy (GAIA). The results reveal three major features. (1) The thermosphere cools about 10 K more around solstices than equinoxes, more at the summer pole than the winter pole. (2) The meridional circulation shifts downward and strongly accelerates by 5–15 m s−1. (3) The tidal activity experiences dramatic changes, with a 40–60% reduction in the semidiurnal tides (SW2) throughout the thermosphere but an 30–50% enhancement in diurnal tides (DW1) below 200 km altitude. The nonmigrating tide DE3 has only minor changes. These changes in temperature, meridional circulation, and tides are persistent features in all seasons and can profoundly affect the spatial distribution and diurnal cycles of the ionospheric responses to CO2 doubling via atmosphere composition and electrodynamics

Event date： 2020.7

Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Online   Country：Japan  

地球の電離圏と宇宙天気の最先端の研究結果を多分野の研究者をわかりやすく解説する。

Event date： 2019.12

Language：English   Presentation type：Oral presentation (general)  

Venue：San Francisco   Country：United States  

Event date： 2019.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Kumamoto   Country：Japan  

Event date： 2019.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Montreal   Country：Canada  

Event date： 2019.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Chiba   Country：Japan  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Honolulu   Country：United States  

Event date： 2018.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Makuhari   Country：Japan  

Thermospheric gravity waves (GWs) in the bottomside F region have been proposed to play
a key role in the generation of equatorial plasma bubbles (EPBs). However, direct observations of such waves are scarce. This study provides a systematic survey of medium-scale (<620 km) neutral atmosphere perturbations at this critical altitude in the tropics, using 4 years of in situ Gravity Field and Steady-State Ocean Circulation Explorer satellite measurements of thermospheric density and zonal wind. The analysis reveals pronounced features on their global distribution and seasonal variability: (1) A prominent three-peak longitudinal structure exists in all seasons, with stronger perturbations over continents than over oceans. (2) Their seasonal variation consists of a primary semiannual oscillations (SAO) and a secondary annual oscillation (AO). The SAO component maximizes around solstices and minimizes around equinoxes,
while the AO component maximizes around June solstice. These GW features resemble those of EPBs
in spatial distribution but show opposite trend in climatological variations. This may imply that stronger medium-scale GW activity does not always lead to more EPBs. Possible origins of the bottomside GWs are discussed, among which tropical deep convection appears to be most plausible.

Event date： 2018.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Hefei   Country：China  

Event date： 2017.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Event date： 2017.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Kyoto   Country：Japan  

Event date： 2017.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Singapore   Country：Singapore  

Event date： 2017.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Makuhari   Country：Japan  

Event date： 2016.12 - 2015.10

Language：English   Presentation type：Oral presentation (general)  

Venue：JAXA   Country：Japan  

Interannual variation of the upper atmosphere

Event date： 2016.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Event date： 2016.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Event date： 2016.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Varna   Country：Bulgaria  

This invited talk summarize the thermosphere and ionosphere response to solar flares, and emphasize recent progresses made by satellite observations.

Event date： 2015.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Bahir Dar   Country：Ethiopia  

Event date： 2015.8 - 2014.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Singapore   Country：Singapore  

Event date： 2015.8 - 2014.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Singapore   Country：Singapore  

Event date： 2015.8 - 2014.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Singapore   Country：Singapore  

Event date： 2015.8 - 2014.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Singapore   Country：Singapore  

Event date： 2015.8 - 2014.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Singapore   Country：Singapore  

Event date： 2015.8 - 2014.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Singapore   Country：Singapore  

Event date： 2015.6 - 2014.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Seattle   Country：United States  

Event date： 2015.5 - 2014.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Makuhari   Country：Japan  

Event date： 2015.5 - 2014.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Makuhari   Country：Japan  

Event date： 2014.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Xi'an   Country：China  

Event date： 2014.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Xian   Country：China  

Event date： 2014.7 - 2014.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Sapporo   Country：Japan  

Event date： 2014.7 - 2014.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Sapporo   Country：Japan  

Event date： 2014.7 - 2014.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Sapporo   Country：Japan  

Event date： 2014.7 - 2014.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Singapore   Country：Singapore  

Event date： 2014.7 - 2014.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Singapore   Country：Singapore  

Event date： 2014.7 - 2014.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Singapore   Country：Singapore  

Event date： 2014.7 - 2014.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Singapore   Country：Singapore  

Event date： 2014.4 - 2014.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Yokohama   Country：Japan  

Event date： 2014.4 - 2014.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Yokohama   Country：Japan  

Event date： 2013.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：高知   Country：Japan  

Event date： 2013.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：高知   Country：Japan  

Event date： 2013.8

Language：English   Presentation type：Symposium, workshop panel (public)  

Venue：NASA 本部   Country：United States  

Event date： 2013.7 - 2013.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Nagoya, Japan   Country：Japan  

Event date： 2013.7 - 2013.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Nagoya, Japan   Country：Japan  

Event date： 2013.7 - 2013.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Nagoya, Japan   Country：Japan  

Event date： 2013.7

Language：English   Presentation type：Oral presentation (general)  

Venue：National Central University, Taiwan   Country：Taiwan, Province of China  

Event date： 2013.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Melaka   Country：Malaysia  

Event date： 2013.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Brisbane   Country：Australia  

Event date： 2013.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Brisbane   Country：Australia  

Event date： 2012.12

Language：English   Presentation type：Oral presentation (general)  

Venue：San Francisco   Country：United States  

Event date： 2012.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Sapporo   Country：Japan  

Event date： 2012.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Sapporo   Country：Japan  

Event date： 2012.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Sapporo   Country：Japan  

Event date： 2012.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Sapporo   Country：Japan  

Event date： 2012.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Sapporo   Country：Japan  

Event date： 2012.8

Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Event date： 2012.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Makuhari   Country：Japan  

Event date： 2012.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Makuhari   Country：Japan  

Event date： 2012.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Makuhari   Country：Japan  

Event date： 2012.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Makuhari   Country：Japan  

Event date： 2012.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Paracas   Country：Peru  

Event date： 2012.2

Presentation type：Oral presentation (general)  

Venue：Kyoto   Country：Japan  

Event date： 2011.12

Presentation type：Oral presentation (general)  

Venue：San Francisco   Country：United States  

Event date： 2011.11

Presentation type：Oral presentation (general)  

Venue：Kobe   Country：Japan  

Event date： 2011.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Taipei   Country：Taiwan, Province of China  

Event date： 2011.6 - 2011.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Melbourne   Country：Australia  

Language：English  

Country：Other  

Faster circulation in a cooler upper atmosphere: GAIA simulation with doubled CO2

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：Other  

DW1 tidal enhancements in the equatorial MLT during 2015 El Nino: the relative role of tidal heating and propagation

Language：Others  

Country：Other  

Response of thermosphere and ionosphere to increasing CO2

Language：Others  

Country：United States  

Response of thermosphere and ionosphere to increasing CO2

Language：English  

Country：Italy  

Atmosphere-Ionosphere Coupling & its Role in Space Weather

Language：Others   Presentation type：Oral presentation (general)  

Country：United States  

Response of thermosphere and ionosphere to increasing CO2

Language：English   Presentation type：Oral presentation (general)  

Country：United States  

Long-term trends in foF2 and foEs over Japan and Antarctic

Language：Others   Presentation type：Oral presentation (general)  

Country：United States  

Long-term trends in foF2 and foEs over Japan and Antarctic

Language：Others   Presentation type：Oral presentation (general)  

Country：United States  

Response of thermosphere and ionosphere to increasing CO2

Event date： 2023.5

Presentation type：Oral presentation (keynote)  

researchmap

Event date： 2022.7

Language：English   Presentation type：Oral presentation (keynote)  

researchmap