Kyushu University Academic Staff Educational and Research Activities Database
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Akimasa Yoshikawa Last modified date:2023.11.27

Professor / Earth Planetary Fluid and Space Sciences
Department of Earth and Planetary Sciences
Faculty of Sciences

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Administration Post
Director of the International Research Center for Space and Planetary Environmental Science

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 Reseacher Profiling Tool Kyushu University Pure
Academic Degree
Doctor of Sciences
Country of degree conferring institution (Overseas)
Field of Specialization
Solar Terrestrial Physics
ORCID(Open Researcher and Contributor ID)
Total Priod of education and research career in the foreign country
Research Interests
  • Studies on Poleward Intensification of aurora expansion caused by moving localized ionospheric flow
    keyword : Composite system, mathematical sciences
  • Studies on formation of Cowling channel connecting from polar to equatorial ionosphere
    keyword : Composite system, mathematical sciences
  • Mathematical science for composite system
    keyword : Composite system, mathematical sciences
  • Studies on the 3D-Cowling effect
    keyword : 3D-current system, Hall current divergence, Sq, auroral electrojet
  • Studies on the generation mechanism of substorm process by using global MI-coupling simulation
    keyword : magnetosphere-ionosphere coupling, substorm, simulation, mathematical science
  • Development of Magnetospheric Storm simulator
    keyword : magnetospheric storm, global simulation, multi-sphere coupling
  • Understanding of the 3D-current system in the geospace
    keyword : geospace, space weather, 3D-current system, global, CPMN, MAGDAS
  • Complex physics in the solar terrestrial system
    keyword : complex system, inter hierarchical coupling, magnetosphere-ionosphere coupling
  • Comparative study of geo-electromagnetic fields using FM-CW radar and MAGDS/CPMN data
    keyword : HF-doppler, ionospheric electric field, ionospheric current system, ionospheric physics
  • magnetospheric physics in the multi-species ion and electron plasma system
    keyword : herman magnetosphere, Jupiter magnetosphere, magnetosphere coupling, space reserch
  • Interaction between MHD waves and ionosphere
    keyword : Hall effect, magnetosphere-ionosphere coupling, energy balance, field-aligned current, inductive coupling
Academic Activities
1. Akimasa Yoshikawa, Ryoichi Fujii, Earth's ionosphere Theory and phenomenology of cowling channels, wiley, 10.1002/9781119324522.ch25, 2018.04, The Cowling channel is a generic name of a current system forming inside a high conductivity band in which a secondary polarization electric field modifies the current flow. The polarization field is excited when a divergent part of Hall current driven by the primary electric field is prevented from flowing out to the magnetosphere as the field-aligned current. The purpose of this chapter is to review the recent development of the Cowling channel model. Recent work provides an extension of the theoretical description of the classical Cowling channel with respect to the following aspects: (1) taking into account the 3D nature of the ionosphere by introducing two current layers at different altitudes, and (2) considering finite length of the Cowling channel by introducing a conductance boundary not only at the meridional borders of the Cowling channel, but also at its zonal boundaries. Using this improved model, we discuss current closure and the energy principle for evolution of the Cowling channel. Energy flow inside the Cowling channel and impact of the polarization effect on Joule dissipation in the more general M-I coupling scheme are also provided. We also clarify how shear Alfvén waves interact to the Cowling channel and their application to the global magnetosphere- ionosphere coupling simulations..
2. Yoshikawa A. and R. Fujii, Earth’s Ionosphere: Theory and Phenomenology of Cowling Channels, in Electric Currents in Geospace and Beyond, John Wiley & Sons, Inc, Hoboken, N.J., 10.1002/9781119324522.ch25, 2018.04, The Cowling channel is a generic name of a current system forming inside a high conductivity band, in which a secondary polarization electric field modifies the current flow. The polarization field is excited when a divergent part of Hall current driven by the primary electric field is prevented from flowing out to the magnetosphere as the field-aligned current (FAC).
The Cowling effect is now well known as enhancement of current flow in the direction of the primary electric field by the secondary Hall current [Chapman, 1956]. The Cowling effect was first investigated by Cowling [1932] in connection with the solar atmosphere. The generation mechanism [Cowling and Boreger, 1948] was adopted to account for equatorial electrojet [Hirono, 1950, Untied, 1967] and auroral electrojet [Boström, 1964]. The Cowling effect has been investigated theoretically and observationally [e.g., Baujohann, 1983; Yasuhara et al., 1985; Haerendel, 2008, Amm et al., [2008]; Amm and Fujii, 2008; Marghitu et al., 2011].
Figure 1 shows traditional picture of two-dimensional Cowling channel model elongated along east-west direction [e.g., Baumjohann, 1983], in which ionospheric Hall and Pedersen conductivity are height-integrated. The primary westward electric field (E1) drives northward Hall current and westward Pedersen current. The southward secondary field (E2) is generated so that the Pedersen current closes the primary Hall current between the conductivity gradients. The secondary Hall current flows in the same direction as the primary Pedersen current and forms the electrojet system.
Generally, it is difficult to specify polarization effects in the ionosphere from ground-based data alone. These data only allow to infer the resultant total electrodynamic fields, but cannot track back the chain of cause and consequence that led to the physical situation which then causes these observed total fields. Thus, using ground-based data alone in most cases we can only state whether an observed situation is consistent or not with the expectations from an “active” polarization effect.
To quantify the Cowling effect, we need to know the relative strength of the polarization electric field to total electric field and to what extent it cancels (closes) the primary Hall current. This problem is complementary to the question: How much curl-free Hall current flows out to the magnetosphere as FAC?
In order to reply to this problem provided by Amm et al., [2008], modeling of Cowling channel has been further developed.
To describe the Cowling channel, Amm et al., [2011] and Fujii et al., [2011] introduce a parameter called the Cowling efficiency. It is defined as a ratio how much of Hall current is confined inside the ionosphere by the secondary Pedersen current excited by the polarization electric field. Definition of Cowling efficiency is practically important. It provides a general way to calculate quantitatively the polarization electric field, if the Cowling efficiency, the conductance, and either primary or the total electric fields are known [Amm et al., 2013].
It has been suggested that to identify the Cowling efficiency for specific phenomenon, one needs to know the impedance of the magnetospheric circuit, which completes the current circuit in the M-I system via FAC [e.g., Fujii et al., 2011]. However, it is questionable to assign a magnetospheric impedance for steady state because the M-I system is always changing dynamically.
The M-I coupling process via shear Alfven waves has been used to investigate the nonstationary FAC closure by ionospheric conducting current [e.g., Scholer, 1970]. Assuming specific electric field configurations of an incident wave, Glaβmeier [1983] and Itonaga and Kitamura [1988] have shown that a secondary polarization field due to gradients of Hall conductance can appear in the reflected wave. Actually, the Alfven wave approach can be used to describe not only local and dynamical phenomena but also more generally global quasi-static M-I coupling processes [Yoshikawa et al., 2010]. Therefore it is very important to understand the how the shear Alfven wave interacts with the Cowling channel.
Yoshikawa et al., [2011a] give a general theory about M-I coupling, independent of specific geometries or specific situations. This theory, based on the Alfven waves used in a way of a basis function for the M-I coupling process, is later applied in Yoshikawa et al., [2013a] and Yoshikawa et al., [2013b] specifically to a Cowling channel situation, but can be applied for any general case.
Most of Cowling channel models introduced so far rely on a thin-sheet ionosphere [e.g., Baujohann, 1983]. However, in a realistic ionospheric E-layer, a vertical distribution of the Pedersen conductivity and Hall conductivity has maximum peak around 125 km altitude and around 110 km altitude, respectively [e.g., Richmond and Thayer, 2000]. In order properly consider the ionospheric current closure, one also takes into account the ionospheric thickness [Amm et al., 2008]. One step in this direction is to assume that the Pedersen and Hall current flow thin layers at different altitudes [Fujii et al., 2011; Amm et al., 2011; Yoshikawa et al., 2011].
The classical picture illustrated in Figure 1 describes divergence-free approximation of auroral electrojet. However, a longitudinal boarder of Cowling channel is also important for considering finite aurora arc formation and Harang reversal region [Harang, 1947; Heppner, 1972; Marghitu et al., 2011], where the auroral electrojet is diverging.
Amm et al., [2008] give a review of the work available in the literature until 2008 regarding following aspects of ionospheric electrodynamics and Magnetosphere-Ionosphere (M-I) coupling:
-Polarization effect in the ionosphere (often referred to as “Cowling effect)”
-Inductive effect in the ionosphere
-The effect of the three-dimensional (3D) nature of the ionosphere for ionospheric electrodynamics
-The consequences of the above mentioned aspects to M-I coupling.
Marghitu, [2012] provides an excellent review for auroral arc electrodynamics, by considering the 1D thin uniform arc, the 2D thick uniform arc, and the non-uniform arc. The various arc features are assembled together in a tentative 3D arc model.
The purpose of this chapter is to review the recent development of Cowling channel model after Amm et al., [2008] and Marghitu, [2012]. Recent work provide an extension of theoretical description of the classical Cowling channel with respect to the following aspects: 1) Taking into account the 3D nature of ionosphere by introducing two current layers at different altitudes, and 2) considering finite length of the Cowling channel by introducing a conductance boundary not only at the meridional borders of Cowling channel, but also at its zonal boundaries. Using this improved model, schematically illustrated in Figure 2 with Cowling efficiency description, we discuss current closure and their energy principle for evolution of Cowling channel. Energy flow inside the Cowling channel and impact of polarization effect on Joule dissipation in more general M-I coupling scheme are also provided. In addition, we also clarify how shear Alfven wave interacts to the Cowling channel and their application to the global magnetosphere-ionosphere coupling simulations..
3. Lysak, R. L. and A. Yoshikawa, Resonant Cavities and Waveguides in the Ionosphere and Atmosphere, Magnetospheric ULF Waves: Synthesis and New Directions, AGU, Washington, D. C., 2006.12.
1. S. S. Starzhinskii, V. M. Nikiforov, @A. Yoshikawa, The Experience of Magnetovariational Sounding in the Arctic: the Laptev Sea Region, Izvestiya, Physics of the Solid Earth, 10.1134/S106935132002010X, 56, 2, 225-237, 2020.03, Abstract—We present the results of magnetovariational soundings at two sites (Tiksi Observatory and Kotelny Island in the Laptev Sea region of the Arctic) and their three-dimensional (3D) inversion using the ModEM program. In the models obtained by the inversion, the conductive heterogeneities are present in the regions of the both sites down to a depth of 200 km in the region of the observatory and 100 km beneath the Kotelny Island. The geoelectric heterogeneities in the model in the region of the observatory are most contrasting and voluminous, whereas beneath the island they are more localized. The correlation between the locations of these heterogeneities at both sites and the features of the geological and geophysical structure of the region is noted. It is shown that the applied algorithm of data processing eliminates the effect of the polar electrojet which provides the possibility to study the geoelectric structure of the region by magnetovariational method..
2. @T. Uozumi, @A. Yoshikawa, S. Ohtani, Formation of a 3-D Oscillatory Current System Associated With Global High-Correlation Pi 2 Event: A Case Study, Journal of Geophysical Research: Space Physics, 10.1029/2019JA026988, 125, 1, 2020.01, We present a typical example of the formation of a three-dimensional (3-D) oscillatory current system associated with a global high-correlation Pi 2 event. The time variation of the field-aligned current (FAC) density in the magnetosphere is estimated using multisatellite magnetic field data in the near-Earth plasma sheet (~10 RE, ~23 MLT). Pi 2 pulsations, which were accompanied with the development of the upward and downward FACs in the substorm current wedge, were observed at mid-latitude stations in the pre-midnight sector (20.6 and 22.6 MLT), and the periodicity of the FAC fluctuations was correlated with the estimated current-density fluctuations in the near-Earth plasma sheet. Compressional signals of the Pi 2 pulsation were observed by an equatorial ground station and a geosynchronous satellite located in the midnight sector (0.1 and 0.4 MLT). A detailed comparison of the Pi 2 waveforms, which were simultaneously observed on the ground and in the near-Earth magnetosphere, revealed high correlations between the fluctuations of the FACs and compressional pulses. These observations strongly suggest the formation of a 3-D oscillatory current system associated with the global high-correlation Pi 2 event. The sources of the oscillatory current system and compressional pulses were confirmed to be closely coupled with one another..
3. Akiko Fujimoto, Akimasa Yoshikawa, Teiji Uozumi, Shuji Abe, Seasonal dependence of semidiurnal equatorial magnetic variation during quiet and disturbed periods, 10th Anniversary International Conference on Solar-Terrestrial Relations and Physics of Earthquake Precursors, STRPEP 2019 E3S Web of Conferences, 10.1051/e3sconf/201912702025, 127, 2019.11, The analysis of 20-year long-term semidiurnal lunar tidal variations gave the evidence that the semidiurnal variations are completely different between the magnetic quiet and disturbed periods. This is the first time that the seasonal dependence of disturbance-time semidiurnal variation has been provided from the analysis of the EE-index. We found the Kp dependence of semidiurnal variation: For full and new moon phase, counter troughs are amplified during disturbance time, possibly related to disturbance dynamo. For all moon phase, there are positive enhancements in dawn and strong depressions after sunset, resulting from the penetration of polar electric filed. For Seasonal dependence, semidiurnal variations are divided to three seasonal groups, and characterized as deep trough, enhanced crest and weak structure for D-solstice, Equinoxes and J-solstice, respectively. There is no significant longitudinal difference between Ancon and Davao, except for the amplitude of semidiurnal variations. The deep troughs occur during D-solstice and the enhanced crests during Equinoxes, at both Ancon and Davao..
4. R Umar, SF Natasha, SSN Aminah, KN Juhari, MH Jusoh, NSA Hamid, MH Hashim, ZM Radzi, AN Ishak, SN Hazmin, WZAW Mokhtar, MKA Kamarudin, H Juahir, A Yoshikawa, Features of horizontal magnetic field intensity over northern island of Malaysia, Indian Journal of Physics, 10.1007/s12648-018-1318-x, 93, 5, 553-564, 2019.05, Magnetic Data Acquisition System (MAGDAS) is a magnetometer initiated by the International Center for Space Weather Science and Education in Kyushu University, Japan, to study space weather. The latest of real-time Magnetic Data Acquisition System/Circum-pan Pacific Magnetometer Network was successfully installed at the East Coast Environmental Research Institute in Universiti Sultan Zainal Abidin, Terengganu, Malaysia, by Kyushu University. This is the fifth magnetometer under the MAGDAS network (geographic latitude and longitude: 5.23°, 103.04° and geomagnetic latitude and longitude: − 4.21°, 175.91°). In this study, the results of data plot obtained at Terengganu (TRE) station were shown to have reliable patterns of geomagnetic elements. The amplitude variations for each component were also proximate with other stations and a standard model. This study compared MAGDAS-II data for the H component with solar wind data (input energy, IMF, dynamic pressure and speed)..
5. R. A. Marshall, L. Wang, G. A. Paskos, G. Olivares-Pulido, T. Van Der Walt, C. Ong, D. Mikkelsen, G. Hesse, B. McMahon, E. Van Wyk, G. Ivanovich, D. Spoor, C. Taylor, A. Yoshikawa, Modeling Geomagnetically Induced Currents in Australian Power Networks Using Different Conductivity Models, Space Weather, 10.1029/2018SW002047, 7, 5, 727-756, 2019.04, Space weather manifests in power networks as quasi-DC currents flowing in and out of the power system through the grounded neutrals of high-voltage transformers, referred to as geomagnetically induced currents. This paper presents a comparison of modeled geomagnetically induced currents, determined using geoelectric fields derived from four different impedance models employing different conductivity structures, with geomagnetically induced current measurements from within the power system of the eastern states of Australia. The four different impedance models are a uniform conductivity model (UC), one-dimensional n-layered conductivity models (NU and NW), and a three-dimensional conductivity model of the Australian region (3DM) from which magnetotelluric impedance tensors are calculated. The modeled 3DM tensors show good agreement with measured magnetotelluric tensors obtained from recently released data from the Australian Lithospheric Architecture Magnetotelluric Project. The four different impedance models are applied to a network model for four geomagnetic storms of solar cycle 24 and compared with observations from up to eight different locations within the network. The models are assessed using several statistical performance parameters. For correlation values greater than 0.8 and amplitude scale factors less than 2, the 3DM model performs better than the simpler conductivity models. When considering the model performance parameter, P, the highest individual P value was for the 3DM model. The implications of the results are discussed in terms of the underlying geological structures and the power network electrical parameters..
6. A Fujimoto, A Yoshikawa, A Ikeda, Global response of Magnetic field and Ionosonde observations to intense solar flares on 6 and 10 September 2017, E3S Web of Conferences, 10.1051/e3sconf/20186201007, 62, 01007, 2018.11, Intense X-ray fluxes during solar flares are known to cause enhanced ionization in the Earth’s ionospheric D, E and F region. This sudden change of ionospheric electron density profile is serious problem to radio wave communication and navigation system. The ground magnetograms often record the sudden change in the sunlit hemisphere during the enhanced X-ray flux, due to the sudden increase in the global ionospheric current system caused by the flare-induced enhanced ionospheric conductivity. These geomagnetic field disturbances are known as ‘‘solar flare effects’’ (SFEs) or geomagnetic crochets [Campbell, 2003]. The typical SFE is increase variation on the equatorial magnetic data. On Ionosonde observation during solar flare event, the High-Frequency (HF) radio wave blackout is often detected in ionogram due to the sudden disturbance in ionosphere. Two intense X-class solar flares occurred on 6 and 10 September 2017. We investigated the magnetic field and Ionosonde responses to the intense solar flare events. Dayside magnetic field variations sudden increased due to the ionospheric disturbance resulting from solar flare. There is no response in night side magnetometer data. The magnitude of SFE (magnetic field) is independent of solar flare x-ray magnitude. We found HF radio wave blackout in ionogram at dayside Ionosonde stations. The duration of blackout is dependent of latitude and local time of Ionosonde stations. There is the different feature of ionogram at night side..
7. A Ikeda, T Uozumi, A Yoshikawa, A Fujimoto, S Abe, Schumann resonance parameters at Kuju station during solar flares, E3S Web of Conferences, 10.1051/e3sconf/20186201012, 62, 01012, 2018.11, We examined the Schumann resonance (SR) at low-latitude station KUJ by comparing with solar X-ray flux and solar proton flux at a geostationary orbit. For intense solar activity in October-November 2003, the reaction of the SR frequency to X-ray enhancement and SPEs was different. The SR frequency in H component increased at the time of the Xray enhancement. The response of SR seems to be caused by the increase of the electron density in the ionospheric D region which ionized by the enhanced solar X-ray flux. In the case of the SPEs, the SR frequency in D component decreased with enhancement of solar proton flux. We suggest that the SPEs caused the decrease of altitude on the ionopheric D region at high-latitude region, and the SR frequency decreased..
8. Akimasa Yoshikawa, Akiko Fujimoto, Akihiro Ikeda, Teiji Uozumi, Shuji Abe, Monitoring of Space and Earth electromagnetic environment by MAGDAS project
Collaboration with IKIR-Introduction to ICSWSE/MAGDAS project, E3S Web of Conferences, 10.1051/e3sconf/20172001013, 20, 2017.10, For study of coupling processes in the Solar-Terrestrial System, International Center for Space Weather Science and Education (ICSWSE), Kyushu University has developed a real time magnetic data acquisition system (the MAGDAS project) around the world. The number of observational sites is increasing every year with the collaboration of host countries. Now at this time, the MAGDAS Project has installed 78 real time magnetometers-so it is the largest magnetometer array in the world. The history of global observation at Kyushu University is over 30 years and number of developed observational sites is over 140. Especially, Collaboration between IKIR is extended back to 1990's. Now a time, we are operating Flux-gate magnetometer and FM-CW Radar. It is one of most important collaboration for space weather monitoring. By using MAGDAS data, ICSWSE produces many types of space weather index, such as EE-index (for monitoring long tern and shot term variation of equatorial electrojet), Pc5 index (for monitoring solar-wind velocity and high energy electron flux), Sq-index (for monitoring global change of ionospheric low and middle latitudinal current system), and Pc3 index (for monitoring of plasma density variation at low latitudes). In this report, we will introduce recent development of MAGDAS/ICSWSE Indexes project and topics for new open policy for MAGDAS data will be also discussed..
9. S. Imajo, Akimasa Yoshikawa, T. Uozumi, Shin Ohtani, A. Nakamizo, P. J. Chi, Application of a global magnetospheric-ionospheric current model for dayside and terminator Pi2 pulsations, Journal of Geophysical Research, 10.1002/2017JA024246, 122, 8, 8589-8603, 2017.08, Pi2 magnetic oscillations on the dayside are considered to be produced by the ionospheric current that is driven by Pi2-associated electric fields from the high-latitude region, but this idea has not been quantitatively tested. The present study numerically tested the magnetospheric-ionospheric current system for Pi2 consisting of field-aligned currents (FACs) localized in the nightside auroral region, the perpendicular magnetospheric current flowing in the azimuthal direction, and horizontal ionospheric currents driven by the FACs. We calculated the spatial distribution of the ground magnetic field produced by these currents using the Biot-Savart law in a stationary state. The calculated magnetic field reproduced the observational features reported by previous studies: (1) the sense of the H component does not change a wide range of local time sectors at low latitudes, (2) the amplitude of the H component on the dayside is enhanced at the equator, (3) the D component reverses its phase near the dawn and dusk terminators, (4) the meridian of the D component phase reversal near the dusk terminator is shifted more sunward than that near the dawn terminator, and (5) the amplitude of the D component in the morning is larger than that in the early evening. We also derived the global distributions of observed equivalent currents for two Pi2 events. The spatial patterns of dayside equivalent currents were similar to the spatial pattern of numerically derived equivalent currents. The results indicate that the oscillation of the magnetospheric-ionospheric current system is a plausible explanation of Pi2s on the dayside and near the terminator..
10. Toshitaka Tsuda, Mamoru Yamamoto, Hiroyuki Hashiguchi, Kazuo Shiokawa, Yasunobu Ogawa, Satonori Nozawa, Hiroshi Miyaoka, Akimasa Yoshikawa, A proposal on the study of solar-terrestrial coupling processes with atmospheric radars and ground-based observation network, Radio Science, 10.1002/2016RS006035, 51, 9, 1587-1599, 2016.09, The solar energy can mainly be divided into two categories: the solar radiation and the solar wind. The former maximizes at the equator, generating various disturbances over a wide height range and causing vertical coupling processes of the atmosphere between the troposphere and middle and upper atmospheres by upward propagating atmospheric waves. The energy and material flows that occur in all height regions of the equatorial atmosphere are named as “Equatorial Fountain.” These processes from the bottom also cause various space weather effects, such as satellite communication and Global Navigation Satellite System positioning. While, the electromagnetic energy and high-energy plasma particles in the solar wind converge into the polar region through geomagnetic fields. These energy/particle inflow results in auroral Joule heating and ion drag of the atmosphere particularly during geomagnetic storms and substorms. The ion outflow from the polar ionosphere controls ambient plasma constituents in the magnetosphere and may cause long-term variation of the atmosphere. We propose to clarify these overall coupling processes in the solar-terrestrial system from the bottom and from above through high-resolution observations at key latitudes in the equator and in the polar region. We will establish a large radar with active phased array antenna, called the Equatorial Middle and Upper atmosphere radar, in west Sumatra, Indonesia. We will participate in construction of the EISCAT_3D radar in northern Scandinavia. These radars will enhance the existing international radar network. We will also develop a global observation network of compact radio and optical remote sensing equipment from the equator to polar region..
11. R. Fujii, O. Amm, Heikki Antero Vanhamaki, Akimasa Yoshikawa, A. Ieda, An application of the finite length Cowling channel model to auroral arcs with longitudinal variations, Journal of Geophysical Research, 10.1029/2012JA017953, 117, 11, 2012.12, A physical process for the latitudinal motion of an auroral arc based on the four-side bound Cowling channel model is proposed. Assuming that an upward field-aligned current (FAC) is associated with the auroral arc that forms a Cowling channel with finite lengths not only latitudinally but also longitudinally and that the upward FAC region is primarily embedded in a purely northward electric field, the primary Hall current driven by the northward electric field accumulates positive excess charges at the eastern edge of the channel and negative charges at the western edge for a perfect or partial Cowling channel with a nonzero Cowling efficiency. The charges produce a westward secondary electric field, indicating that a westward electric field can thus be produced by a purely northward primary electric field. This secondary electric field moves the arc with its magnetospheric source drifting together with the magnetospheric plasmas equatorward and simultaneously produces the electric field outside the channel that moves the downward FAC equatorward of the upward FAC region equatorward together with the upward FAC. Thus, the whole 3-D current system is expected to move equatorward as often observed in the afternoon auroral zone..
12. Heikki Antero Vanhamaki, Akimasa Yoshikawa, O. Amm, R. Fujii, Ionospheric Joule heating and Poynting flux in quasi-static approximation, Journal of Geophysical Research, 10.1029/2012JA017841, 117, 8, 2012.01, Energy flow is an important aspect of magnetosphere-ionosphere coupling. Electromagnetic energy is transported as Poynting flux from the magnetosphere to the ionosphere, where it is dissipated as Joule heating. Recently Richmond derived an "Equipotential Boundary Poynting Flux (EBPF) theorem", that the Poynting flux within a flux tube whose boundary is an equipotential curve is dissipated inside the ionospheric foot point of the flux tube. In this article we study Richmond's EBPF theorem more closely by considering the curl-free and divergence-free parts as well as the Hall and Pedersen parts of the ionospheric current system separately. Our main findings are that i) divergence-free currents are on average dissipationless, ii) the curl-free Pedersen current is responsible for the whole ionospheric Joule heating and iii) pointwise match between vertical Poynting flux and ionospheric Joule heating is broken by gradients of Hall and Pedersen conductances. Results i) and ii) hold when integrated over the whole ionosphere or any area bounded by an equipotential curve. The present study is limited to quasi-static phenomena. The more general topic of electrodynamic Joule heating and Poynting flux, including inductive effects, will be addressed in a future study..
13. Akimasa Yoshikawa, O. Amm, Heikki Antero Vanhamaki, R. Fujii, A self-consistent synthesis description of magnetosphere-ionosphere coupling and scale-dependent auroral process using shear Alfvén wave, Journal of Geophysical Research, 10.1029/2011JA016460, 116, 8, 2011.01, In order to correctly describe the dynamical behavior of the magnetosphere-ionosphere (MI) coupling system and the scale-dependent auroral process, we develop a synthesis formulation that combines the process of (1) the inverse Walen separation of MHD disturbance into parallel- and antiparallel-propagating shear Alfvén wave to the ambient magnetic field, (2) the shear Alfvén wave reflection process including (3) the scale-dependent electrostatic coupling process through the linearized Knight relation, (4) two-layer ionosphere model, and (5) dynamic conductance variations. A novel procedure that applies the inverse Walen relation to the incompressional MHD disturbances at the inner boundary of the MHD region enables to extract the component of the shear Alfvén wave incident to the ionosphere. The extracted incident electric field supplies an electromotive force for the generation of the MI coupling system, and the reflected electric field is generated such that it totally satisfies the synthesis MI-coupling equation. A three-dimensional ionospheric current system is represented by a two-layer model in which the Pedersen and the Hall current are confined in the separated layers, which are connected by field-aligned currents driven by the linear current-voltage relation between two layers. Hence, our scheme possibly reproduces two types of the scale-dependent MI-decoupling process of the perpendicular potential structure: due to the parallel potential drop at the auroral acceleration region and the other due to the parallel potential differences inside the ionosphere. Our newly formulation may be well suited for description of scale-dependent auroral process and mesoscale ionospheric electrodynamics interlocked with the dynamical development of magnetospheric processes..
14. O. Amm, R. Fujii, K. Kauristie, A. Aikio, Akimasa Yoshikawa, A. Ieda, Heikki Antero Vanhamaki, A statistical investigation of the Cowling channel efficiency in the auroral zone, Journal of Geophysical Research, 10.1029/2010JA015988, 116, 2, 2011.01, The Cowling channel mechanism describes the creation of a secondary polarization electric field at sharp conductance boundaries in the ionosphere due to excess charges for the case in which the release of these charges to the magnetosphere is fully or partially impeded. The secondary currents generated by the polarization electric field effectively modify the effective ionospheric conductivity inside the Cowling channel. While the Cowling mechanism is generally accepted for the equatorial electrojet, there is a long-standing discussion about the importance of this mechanism and its efficiency in the auroral electrojet. We present a statistical investigation that enables us to identify the most probable geospace conditions and MLT locations for a high Cowling efficiency. This investigation is based on more than 1600 meridional profiles of data from the Magnetometers-Ionospheric Radars-All-sky Cameras Large Experiment (MIRACLE) network in Scandinavia, in particular, ground magnetic field data from the International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer network and electric field data from the Scandinavian Twin Auroral Radar Experiment (STARE) radar, supported with pointwise ionospheric conductance measurements from the European Incoherent Scatter (EISCAT) radar. We analyze the data in the framework of a 3-D ionospheric model, but our data set is filtered so that only electrojet-type situations are included so that the gradients of all measured quantities in longitudinal direction can be neglected. The analysis results in a steep peak of high Cowling channel efficiency probability in the early morning sector (0245-0645 MLT), with the largest probability around 0500 MLT and for medium and high geomagnetic activity. In agreement with an earlier single-event study by Amm and Fujii (2008), this indicates that the Cowling mechanism may be most effective in the early morning part of the central substorm bulge. Further, our analysis results in an almost monotonic increase of the probability of high Cowling channel efficiency with increasing geomagnetic activity..
15. Y. Yamazaki, K. Yumoto, M. G. Cardinal, B. J. Fraser, P. Hattori, Y. Kakinami, J. Y. Liu, K. J.W. Lynn, R. Marshall, D. McNamara, T. Nagatsuma, V. M. Nikiforov, R. E. Otadoy, M. Ruhimat, B. M. Shevtsov, K. Shiokawa, S. Abe, T. Uozumi, Akimasa Yoshikawa, An empirical model of the quiet daily geomagnetic field variation, Journal of Geophysical Research, 10.1029/2011JA016487, 116, 10, 2011.01, An empirical model of the quiet daily geomagnetic field variation has been constructed based on geomagnetic data obtained from 21 stations along the 210 Magnetic Meridian of the Circum-pan Pacific Magnetometer Network (CPMN) from 1996 to 2007. Using the least squares fitting method for geomagnetically quiet days (Kp ≤ 2+), the quiet daily geomagnetic field variation at each station was described as a function of solar activity SA, day of year DOY, lunar age LA, and local time LT. After interpolation in latitude, the model can describe solar-activity dependence and seasonal dependence of solar quiet daily variations (S) and lunar quiet daily variations (L). We performed a spherical harmonic analysis (SHA) on these S and L variations to examine average characteristics of the equivalent external current systems. We found three particularly noteworthy results. First, the total current intensity of the S current system is largely controlled by solar activity while its focus position is not significantly affected by solar activity. Second, we found that seasonal variations of the S current intensity exhibit north-south asymmetry; the current intensity of the northern vortex shows a prominent annual variation while the southern vortex shows a clear semi-annual variation as well as annual variation. Thirdly, we found that the total intensity of the L current system changes depending on solar activity and season; seasonal variations of the L current intensity show an enhancement during the December solstice, independent of the level of solar activity..
16. R. Fujii, O. Amm, Akimasa Yoshikawa, A. Ieda, Heikki Antero Vanhamaki, Reformulation and energy flow of the Cowling channel, Journal of Geophysical Research, 10.1029/2010JA015989, 116, 2, 2011.01, The question to which extent the divergence of the Hall current can be connected to the Pedersen current or to the closure current in the magnetosphere through field-aligned currents (FACs), that is, the Cowling channel process in the polar region, has long been debated but not fully understood. The present study reformulates the Cowling channel by introducing a two-layer model consisting of Hall and Pedersen conductivity layers with channel boundaries not only in the direction perpendicular to the channel but also in the direction along it. This new model enables us to better and more physically understand the connection between the Hall current, Pedersen current, and FAC. In particular, the finiteness of the channel along its direction enables us to understand that the primary nonzero electric field along the channel and FACs at the channel boundaries that faced each other in the channel direction carries the necessary energy for the Hall current to set up the secondary electric field from the magnetosphere. A case for a possible connection between the Pedersen and Hall currents is shown based on a polar current system derived from the Kamide-Richmond-Matsushita method. A more comprehensive analysis based on data is presented in the companion paper..
17. Akimasa Yoshikawa, A. Nakamizo, O. Amm, Heikki Antero Vanhamaki, R. Fujii, Y. M. Tanaka, T. Uozumi, K. Yumoto, S. Ohtani, Self-consistent formulation for the evolution of ionospheric conductances at the ionospheric e region within the M-I coupling scheme, Journal of Geophysical Research, 10.1029/2011JA016449, 116, 9, 2011.01, We formulate the evolution of ionospheric conductivity in the framework of 3-D M-I coupling. Two important physical processes are taken into account. One is the ionization process by precipitating mono-energetic particles, which are accelerated by parallel-potential drops in the auroral acceleration region. The other process reflects the fact that part of field-aligned current (FAC) carried by electrons is closed with a perpendicular ionic current. Here, whereas the electric current is divergence-free, the divergence of electron current is finite. Therefore, the ionospheric electron density changes, and so does the conductivity. If the energy of electron precipitation is below ∼10 eV, this second process plays an important role in plasma transportation, production, and evacuation processes. In this case the density variation does not extend in space at the perpendicular electron velocity, but it rather moves at the ion perpendicular velocity. If the energy of electron precipitation is above ∼1 keV, in contrast, the precipitation has a nonlinear effect on plasma evolution. That is, the propagation speed of the density variation increases with increasing upward-FAC density, and the propagation takes place in the direction of the converging current into the upward FAC region. The Cowling effect on the plasma evolution process is crucially important. Our formulation is more general than the previous studies and is not limited to certain geometries, current component or interaction modes between the ionosphere and magnetosphere. It is therefore better-suited for describing the self-organized M-I coupling system, which evolves with current systems, conductivity, and magnetospheric processes interacting with each other..
18. Tanaka T., A. Nakamizo, A. Yoshikawa , S. Fujita, H. Shinagawa, H. Shimazu, T. Kikuchi, K. Hashimoto, Substorm convection and current system deduced from the global simulation, J. Geophys. Res., 10.1029/2009JA014676, 115, A05220, J. Geophys. Res. 115, A05220, doi:10.1029/2009JA014676, 2010.12.
19. Yoshikawa A., H. Nakata, A. Nakamizo, T. Uozumi, M. Itonaga, S. Fujita, K. Yumoto, and T. Tanaka, Alfvenic-coupling algorithm for global and dynamical magnetosphere-ionosphere coupled system, J. Geophys. Res., 10.1029/2009JA014924, 115, A04211, J. Geophys. Res., 115, A04211, doi:10.1029/2009JA014924, 2010.03.
20. Yoshikwa A., H. Nakata, A. Nakamizo, T. Uozumi, M. Itonaga, and K. Yumoto, A new magnetospherere- ionosphere coupling scheme for temporal and global magnetospheric MHD simulations, Mem. Fac. Sci., Kyushu Univ., Ser. D, Earth & Planet.Sci.,Vol, XXXII, No2, 87-94, XXXII, 2, 87-94, Vol, XXXII, No2, 87-94, 2009.03.
21. T. Uozumi, K. Yumoto, K. Kitamura, S. Abe, Y. Kakinami, M. Shinohara, Akimasa Yoshikawa, Hideaki Kawano, T. Ueno, T. Tokunaga, D. McNamara, J. K. Ishituka, S. L.G. Dutra, B. Damtie, V. Doumbia, O. Obrou, A. B. Rabiu, I. A. Adimula, M. Othman, M. Fairos, R. E.S. Otadoy, A new index to monitor temporal and long-term variations of the equatorial electrojet by MAGDAS/CPMN real-time data
EE-index, Earth, Planets and Space, 10.1186/BF03352828, 60, 7, 785-790, 2008.01, A new index, EE-index (EDst, EU, and EL), is proposed to monitor temporal and long-term variations of the equatorial electrojet by using the MAGDAS/CPMN real-time data. The mean value of the H component magnetic variations observed at the nightside (LT = 18-06) MAGDAS/CPMN stations along the magnetic equatorial region is found to show variations similar to those of Dst; we defined this quantity as EDst. The EDst can be used as a proxy of Dst for the real-time and long-term geospace monitoring. By subtracting EDst from the H component data of each equatorial station, ir is possible to extract the Equatorial Electrojet and Counter Electrojetcomponents, which are defined as EU and EL, respectively..
22. Terumasa Tokunaga, Hiroko Kohta, Akimasa Yoshikawa, Teiji Uozumi, Kiyohumi Yumoto, Global features of Pi 2 pulsations obtained by independent component analysis, Geophysical Research Letters, 10.1029/2007GL030174, 34, 14, 2007.07, Ground Pi 2 pulsations are mixtures of several components reflecting (1) propagations of fast and shear Alfvén wave, (2) resonances of plasmaspheric/magnetospheric cavity and magnetic field lines, and (3) tansformations to ionospheric current systems. However, it has been unclear how they coupled with each other and how their signals are distributed at different latitudes. The present work is intended to pilot the future possibilities whether we can identify the global system of Pi 2 pulsations by Independent Component Analysis (ICA). We have successfully decomposed an isolated Pi 2 event on a quiet day observed at the CPMN stations into two components. One was the global oscillation that occurs from nightside high to equatorial latitudes with the common waveform and has an amplitude maximum at nightside high latitude. Another component was localized at nightside high latitudes. Its amplitudes were quite weak at low latitudes, but were enhanced near dayside dip equator..
23. Obana, A. Yoshikawa, J.V. Olson, R.J. Morris, B.J. Fraser, S.I. Solovyev, and K. Yumoto, Techniques to investigate the ionospheric effect on ULF waves, Proceeding of The fifth Workshop on Applications of Radio Science (WARS) obart Australia, on Feb. 18-20, 2004, CD-ROM, H12, 2004.02.
24. Abe S., K. Yumoto, H. Kawano, A. Yoshikawa, Y. Obana, S. I. Solovyev, D.G. Baishev, J.V. Olson, E.W. Worthington, and the Circum-pan Pacific Magnetometer Network Group, The Diagnosis of the Plasmapause by Ground Magnetometer Network Observation at Multiple Local Times, International Symposium on Information Science and Electrical Engineering 2003, Nov.13-14, 2003, ACROS Fukuoka, Fukuoka, Japan, 534-536, 2003.11.
25. Kitamura. K., H. Kawano, S. Ohtani, A. Yoshikawa, K. Yumoto, and the Circum-pan Pacific Magnetometer Network Group, Quasi-periodic Substorms during Recovery Phase of Magnetic Storm for Space Weather Study, 354-357, 2003.11.
26. Obana Y., A. Yoshikawa, J.V. Olson, R.J. Morris, B.J. Fraser, S.I. Solovyev and K. Yumoto, Environment Factors of PC 4 Amplitudes Observed at the CPMN Stations, International Symposium on Information Science and Electrical Engineering 2003, Nov.13-14, 2003, ACROS Fukuoka, Fukuoka, Japan, 256-258, 2003.11.
27. Yoshikawa A., H. Kohta, M.I tonaga, T. Uozumi, K. Yumoto, Inegrated Analysis of Coordinated Ground Magnetic Field Data for Space Weather Study, International Symposium on Information Science and Electrical Engineering 2003, Nov.13-14, 2003, ACROS Fukuoka, Fukuoka, Japan, 114-117, 2003.11.
28. Takasaki S., H. Kawano, Y. Tanaka, A. Yoshikawa, M. Seto, M. Iizima, and K. Yumoto, Plasma Distribution in the Low-L part of the Plasma sphere during Magnetic Storms, International Symposium on Information Science and Electrical Engineering 2003, Nov.13-14, 2003, ACROS Fukuoka, Fukuoka, Japan, 253-255, 2003.11.
29. Yoshikawa, A., M. Itonaga and K. Yumoto, On the energy of the poloidal magnetic field near the ionosphere, Advances in Polar Upper Atmospheric Research, No.16, 45-58, 2002.01.
30. M. Itonaga, A. Yoshikawa, K. Yumoto, S. Fujita and H. Nakata, A study on the generation of field-aligned current in the magnetosphere, Mem. Fac. Sci., Kyushu Univ., Ser. D, Earth and Planet. Sci., Vol, XXXI, No1, 1-9, 2000.01.
31. M. Itonaga, Akimasa Yoshikawa, K. Yumoto, One-dimensional transient response of the inner magnetosphere at the magnetic equator, 2. analysis of waveforms, Earth, Planets and Space, 49, 1, 49-68, 1997.02, Under a model of altitude distribution of the Alfvén speed VA, one-dimensional transient response of the inner magnetosphere at the magnetic equator to earthward propagating impulse- and step-like MHD disturbances is considered. The waveforms of transient compressional oscillations due to these disturbances at some L shells are directly simulated by a numerical inversion of the Laplace transform with orthonormal Laguerre functions. The present paper concentrates on the analysis of waveforms. Then, it is verified that the compressional oscillations are due to the poles of the system under consideration. The oscillation arising from the cavity resonance all over the inner magnetosphere is most dominant. However, its amplitude becomes smaller as the characteristic time scale T of an incident disturbance grows large, and it is negligibly small for T greater than several times of eigenperiod of the resonance. On the other hand, when T is relatively small (e.g., T £10 s), the oscillations due to the cavity resonances trapped around the trough in VA are outstanding. It is also found that the relative phase between the cavity-mode oscillations all over the inner magnetosphere at the earth's surface and another L shell increases monotonically with L when the inner magnetosphere has no strong gradient or a strong positive gradient of VA at its outer boundary. However, the relative phase is nearly zero and nearly 180 inside and outside a specific L shell, respectively, when the inner magnetosphere has a strong negative gradient at its outer boundary. The one-dimensional cavity-mode type resonance of the inner magnetosphere is certainly a cause of equatorial Pi2 pulsations. However, some constituents of the Pi2's may be not cavity-mode oscillations but quasi-steady-state oscillations forced by some damped sinusoidal waves incident on the outer boundary of the inner magnetosphere..
32. M. Itonaga, Akimasa Yoshikawa, K. Yumoto, One-dimensional transient response of the inner magnetosphere at the magnetic equator, 1. transfer function and poles, Earth, Planets and Space, 10.5636/jgg.49.21, 49, 1, 21-48, 1997.01, One-dimensional transient response of the inner magnetosphere at the magnetic equator is investigated using two models of altitude distribution of the Alfvén speed VA- The present paper concentrates on the transfer function of the system under consideration and its poles, which govern the transient response of the system. The poles, which are mathematical counterparts of the cavity resonances, appear owing to the inhomogeneity of VA and their locations depend on the altitude distribution of VA as well as the position of external source (or outer boundary of the inner magnetosphere). Even if there exists no strong Alfvén velocity gradient at the outer boundary, an observable cavity-mode oscillation in the Pi2 range can be excited because of the existence of a strong gradient of the plasmapause within the inner magnetosphere. However, the existence of a strong gradient at the outer boundary brings about a long-lived nature of the cavity-mode oscillation as well as calls some new poles into existence. While the surface of the solid earth forms the inner boundary at which the almost perfect reflection of wave takes place, the ionosphere is of secondary importance as a reflector of wave. The existence of the solid earth plays an essential role in the observability of the compressional oscillation arising from the cavity resonance all over the inner magnetosphere. The real part of each pole has a negative value, meaning that the cavity-mode oscillation decays with a damping factor of absolute value of the real part of the pole. Such a damping is primarily due to the leakage of energy through the outer boundary of the inner magnetosphere..
33. M. Itonaga, Akimasa Yoshikawa, The excitation of shear alfvén wave and the associated modulation of compressional wave in the inner magnetosphere, Earth, Planets and Space, 10.5636/jgg.48.1451, 48, 11, 1451-1459, 1996.06, Two basic but novel equations directly describing the generation of shear Alfvén and compressional waves in the inner magnetosphere filled with a cold magnetized plasma are derived. The shear Alfvén wave is characterized by the field-aligned current and the compressional wave by the compressional component of the magnetic field. Such a generation arises from the effects of inhomogeneous Alfvén speed and curvilinear field line. Around the magnetic equator, if the Alfvén speed is inversely proportional to a power of the geocentric distance, these effects have magnitudes of the same order and their signs are identical. Considered in the present study is a situation that the earthward propagating compressional wave is launched from a large scale oscillating current wedge centered at midnight and symmetric about the magnetic equator. Then, it is found that the field-aligned current excited around the equator by the compressional wave has opposite senses in direction in the northern and southern hemispheres, in the pro- and post-midnight sectors as well as just inside the plasmapause and in its surrounding regions. As a result of the excitation of shear Alfvén wave, two types of oscillations appear on a field line: One is a forced oscillation and the other is an eigenoscillation. Although a modulation of the compressional wave may be caused locally (or microscopically) around the equator by the eigenoscillation of field line, the modulation can be globally (or macroscopically) neglected. So far as the propagation along the source longitude (source-earth line) around the equator is concerned, the coupling between compressional and shear Alfvén waves can be almost neglected and so one-dimensional response of the inner magnetosphere around the equator plays a significant role in the compressional oscillation..
34. Yoshikawa, A., M. Itonaga and T.-I.Kitamura, On the coupled effect between the field aligned and ionospheric current, Proceeding of Eight International Symposium on Solar Terrestrial Physics, June 5-10, 1994, Sendai, Japan, 155-159, 1994.06.
35. Yoshikawa, A., M. Itonaga and T.-I.Kitamura, Effect of the ionospheric induction current on magnetohydrodynamic waves in the magnetosphere, Proceedings of the NIPR Symposium on Upper Atmosphere Physics, Vol.17, No.8, 49-59, 1995, 1995.01.
36. Itonaga, M., T.-I.Kitamura and A. Yoshikawa, Interaction between hydromagnetic waves and the anisotropically conducting ionosphere, Journal of Geomagnetism and Geoelectricity, 47, 5, 459-474, Vol.47, No.5, 459-474, 1995, 1995.01.
37. Itonaga, M., and A. Yoshikawa, Discrete spectral structure of low latitude and equatorial Pi2 pulsations,, Journal of Geomagnetism and Geoelectricity, Vol.44, No.3, 253-259, 44, 3, 253-259, 1992.01.
Works, Software and Database
1. .
1. Higuchi, H, and A. Yoshikawa, Electron acceleration mechanism in "ionospheric polarized Poleward Boundary Intensification": A new validation with 3-dimensional fluid electron acceleration simulators, American Geophysics Union Fall Meeting 2021, 2021.12.
2. M. Hayashi, A.Yoshikawa, A.Fujimoto, S.Ohtani, Research on the Poler to Mid-latitude Ionospheric Response During Substorm based on mid-latitude electric field and global magnetic field observations, American Geophysics Union Fall Meeting 2021, 2021.12.
3. Takayama Kumi, Yoshikawa Akimasa , Principal Component Analysis for Extracting Variations due to Sq Current and Atmospheric Tides from Magnetic Field Data, American Geophysics Union Fall Meeting 2021, 2021.12.
4. Yasunaga Akihiro、Akimasa Yoshikawa, and Fujimoto Akiko, Research on the unique Solar Flare Effect (SFE*) at the dip equator around local noon, AOGS Annual Virtual Meeting 2021, 2021.08.
5. Takayama Kumi, Yoshikawa Akimasa, and Miyoshi Yasunobu, Quasi-6-Day Wave Effect on Electric Conductivity, Electric field, and Current with GAIA model, AOGS Annual Virtual Meeting 2021, 2021.08.
6. #M.Hayashi, @A.Yoshikawa, A.Fujimoto, S.Ohtani,, Research for formation of global current system during substorm through observation of ionospheric response at mid-latitudinal region, AOGS Annual Virtual Meeting 2021, 2021.08.
7. 山本 衛、橋口 浩之、横山 竜宏、宮岡 宏、小川 泰信、塩川 和夫、野澤 悟徳、@吉川 顕正、津田 敏隆, Study of coupling processes in the solar-terrestrial system, Japan GeoScience Meeting 2021, 2021.06.
8. 惣宇利 卓弥、新堀 淳樹、大塚 雄一、津川 卓也、西岡 未知、@吉川 顕正, Generation mechanisms of plasma density irregularity from equatorial to midlatitude ionosphere during a geomagnetic storm on 21 and 22 December 2014, Japan GeoScience Meeting 2021, 2021.06.
9. 大矢 浩代、折戸 雄飛、土屋 史紀、山本 真行、中田 裕之、@吉川 顕正, D-region ionospheric effects for 2016 eruptions of Mt. Aso using LF transmitter signals, Japan GeoScience Meeting 2021, 2021.06.
10. 藤本 晶子、@阿部 修司、御厨 徹、池田 昭大、@吉川 顕正, Multiple equatorial ionospheric observation project based on FMCW radar combining MAGDAS/SDR-based scintillation detector, Japan GeoScience Meeting 2021, 2021.06.
11. @吉川 顕正、#橋本 翼、中溝 葵、大谷 晋一, Development of a novel method for extracting the geometrical properties of the magnetic vector fields towards the era of multi-point satellite observations, Japan GeoScience Meeting 2021, 2021.06.
12. 塩川 和夫, 三好 由純, @吉川 顕正、中村 卓司, 太陽地球系物理学科学委員会(SCOSTEP)の活動と展望:学術会議を通した国際活動の推進, Japan GeoScience Meeting 2021, 2021.06.
13. ラナシンハ マンジュラ, 藤本 晶子, @吉川 顕正, ジャヤラトナ チャンダ, Seasonal dependence of dusk-side equatorial IHFACs polarity during solar cycle 23-24, Japan GeoScience Meeting 2021, 2021.06.
14. 中溝 葵, @吉川 顕正, 中田 裕之, 深沢 圭一郎, 田中 高史, Development of a new M-I coupling algorithm in global MHD magnetosphere simulation: Alfvénic-Coupling, Japan GeoScience Meeting 2021, 2021.06.
15. @Akimasa Yoshikawa, Modeling of magnetosphere-ionosphere-atmosphere system for investigation of coupling process in the space-terrestrial transition region, Japan GeoScience Meeting 2021, 2021.06.
16. @Kirolosse Mina Girgis, @Tohru Hada, @Shuichi Matsukiyo, @Akimasa Yoshikawa, , Numerical Proton Flux Response in South Atlantic Anomaly during Geomagnetic Storm, Japan GeoScience Meeting 2021, 2021.06.
17. #森澤将、@吉川顕正、大谷晋一, 夜側オーロラオーバルの極側境界で起こるオーロラ増光現象の発生過程における電離圏分極の数値解析, Japan GeoScience Meeting 2021, 2021.06.
18. #伊集院拓也、@吉川顕正, IGRFモデルを用いた3次元全球電離圏静電ポテンシャルソルバーの開発, Japan GeoScience Meeting 2021, 2021.06.
19. #Yasunaga Akihiro、Fujimoto Akiko、@Yoshikawa Akimasa, Study on the Solar Flare Effect (SFE*) of equatorial electrojet around local noon, Japan GeoScience Meeting 2021, 2021.06.
20. #Takayama Kumi, @Yoshikawa Akimasa, and @Miyoshi Yasunobu, Seasonal Dependence of the Quasi-6-Day Oscillation in Sq-EEJ Current System, Japan GeoScience Meeting 2021, 2021.06.
21. #Higuchi, H. and @A. Yoshikawa, , Exploring the Electron Acceleration Mechanism in the Poleward Boundary Intensification, Japan GeoScience Meeting 2021, 2021.06.
22. M.Hayashi, A.Yoshikawa, A.Fujimoto , S. Ohtani, Investigation of the mid-latitude ionospheric response during substorm based on magnetic and electric field observations, Japan GeoScience Meeting 2021, 2021.06.
23. 中溝 葵, 吉川 顕正, 大谷 晋一, 田中 高史, Alfvénic disturbances generated by the ionospheric polarization and the convection reversal in the magnetosphere, JpGU-AGU Joint Meeting 2020, 2020.07.
24. 吉川 顕正, 中溝 葵, 大谷 晋一, Causality for formation of electromagnetic channel from Polar to Equatorial Ionosphere, JpGU-AGU Joint Meeting 2020, 2020.07.
25. 吉川 顕正, 河野 英昭, 阿部 修司, 魚住 禎司, 藤本 晶子, 池田 昭大, 樺澤 大生, 黒木 智, 林 萌英, 高山 久美, 中溝 葵, Ohtani Shinichi, Investigation of global electromagnetic coupling from polar to equatorial ionosphere, JpGU-AGU Joint Meeting 2020, 2020.07.
26. 樺澤 大生, 吉川 顕正, 魚住 禎司, 藤本 晶子, 阿部 修司, MAGDAS9システムの10Hzデータによる、Pc2脈動の全球的発生分布特性解明, JpGU-AGU Joint Meeting 2020, 2020.07.
27. 高山 久美, 三好 勉信, 吉川 顕正, Sq・EEJ電流系における6日振動現象に着目した大気圏ー電離圏の上下結合の研究, JpGU-AGU Joint Meeting 2020, 2020.07.
28. 林 萌英, 吉川 顕正, 藤本 晶子, 大谷 晋一, 磁気圏電離圏全球結合系解明に向けたイオノグラムの自動読み取り, JpGU-AGU Joint Meeting 2020, 2020.07.
29. Yoshimasa Tanaka, Yasunobu Ogawa, Akira Kadokura, Takanori Nishiyama, Akimasa Yoshikawa, Bjorn Gustavsson, Kirsti Kauristie, Carl-fredrik, Enell, Urban Brandstrom, Tima Sergienko, Alexander Kozlovsky, Tero Raita, Vanhamaki Heikki, Study on auroral 3D structure in the northen Europe, Sixth International Symposium on Arctic Research (ISAR-6), Online, 2020.03.
30. Ikeda A., T. Uozumi, A. Yoshikawa, A. Fujimoto, and S. Abe, Diurnal and seasonal variations in the Schumann Resonance observed at Kuju Japan, AGU fall meeting, 2019.12.
31. Aoi Nakamizo and Akimasa Yoshikawa, Deformation of ionospheric potential pattern by ionospheric Hall polarization, SuperDARN Workshop 2019, Fuji, 2019.06, The present study shows that the ionospheric Hall polarization can deform the high-latitude ionospheric convection field, which is widely considered to be a manifestation of the convection field in the magnetosphere.
We perform the Hall polarization field separation with a potential solver by changing the conductance distribution step- by-step from a uniform one to a more realistic one.
We adopt dawn-dusk and north-south symmetric distributions of conductance and region 1 (R1) field-aligned current (FAC).
The pair of the primary field of the R1 system and each gradient of Hall conductance generates the Hall polarization field and consequently causes potential deformations as follows.
(a) The equatorward gradient causes clockwise rotation.
(b) The gradient across the terminator, together with the effect of the equatorward gradient, causes the dawn-dusk asymmetry.
(c) The high conductance band in the auroral region causes kink-type deformations.
In particular, a nested structure at the equatorward edge of the band in the midnight sector well resembles the Harang Reversal.
Result (a) can explain the clockwise bias inexplicable by the IMF-By effect alone, the combination of (a) and (b) can explain the clearness and unclearness in the round or crescent shapes of the dawn-dusk cells depending on the IMF-By polarity, and (c) suggests that the ionosphere may not need the upward-FAC for the formation of the Harang Reversal.
We suggest that the final structure of the ionospheric potential is established by the combined effects of both the magnetospheric requirements (external causes) and ionospheric polarization (internal effect)..
32. Akimasa Yoshikawa, MAGDAS project: Research for global and local electromagnetic coupling from polar to equatorial ionosphere, SuperDARN Workshop 2019, Fuji, 2019.06, International Center for Space Weather Science and Education (ICSWSE) of Kyushu University is a research institute that conducts academic research and education in space weather and related fields. We have constructed an observation network known as the "MAGDAS/CPMN (MAGnetic Data AcquisitionSystem/Circum-pan Pacific Magnetometer Network)" in international collaboration with more than 60 organizations, including those in developing countries. Currently, over 80 magnetometers and 4 FM-CW (Frequency Modulated Continuous Wave) radars have been installed all over the world. To understand the active role of ionospheric dynamics on the global and local Magnetosphere-Ionosphere coupling from polar to equatorial ionosphere, we conduct integrated studies of theory, numerical simulation, in-situ magnetosphere observation, and global ionosphere observation by MAGDAS. Especially, the ionospheric Hall effect strongly controls the spatiotemporal evolution of the M-I coupling system. Generation of polarization electric field at conductance gradient regions causes rotation, shear, and acceleration/deceleration of ionospheric convection in both local and global manners. The ionospheric polarization field activates upward shear Alfven wave that could cause ionospheric driven magnetospheric dynamics and induce a new type of M-I coupled current system. Generation of induction electric field at the wavefront of ionospheric disturbances enables the electric field of electrostatic potential type to propagate horizontally as a result of coupling between magnetosonic mode and shear Alfven mode induced by multistep Hall effect in a time domain, at the ionospheric E-layer. Such a combined effect of ionospheric Hall polarization and induction on the ionospheric dynamics is a key element for understanding the formation process of the global current system from polar to equatorial ionosphere. In this talk, we will discuss how to identify elementary components of Hall-polarization and induction effect (generalized Cowling effect) from coupled phenomena, and the possibility of collaborative studies between SuperDARN and MAGDAS project to further understand active role of ionospheric dynamics..
33. Akimasa Yoshikawa, Revisiting the energy conversion process of Birkeland current, 日本地球惑星科学連合2019年大会, 2019.05.
34. 藤本 晶子, 池田 昭大, 吉川顕正, Latest installation of FM-CW radar in Peru, 日本地球惑星科学連合2019年大会, 2019.05.
35. 樺澤 大生, 吉川 顕正, 魚住 禎司, 藤本 晶子, 阿部 修司, MAGDAS9システムの10Hzデータによる,Pc1-2脈動の全球分布特性解明, 日本地球惑星科学連合2019年大会, 2019.05.
36. 吉川 顕正, 樺澤 大生, 魚住 禎司, 藤本 晶子, 阿部 修司, Development of MAGDAS project: Search for global electromagnetic coupling from polar to equatorial ionosphere, 日本地球惑星科学連合2019年大会, 2019.05.
37. 山本 衛, 橋口 浩之, 横山 竜宏, 宮岡 宏, 小川 泰信, 塩川 和夫, 野澤 悟徳, 吉川 顕正, 津田 敏隆, 太陽地球系結合過程の研究基盤形成, 日本地球惑星科学連合2019年大会, 2019.05.
38. Mio Nakahara, Akimasa Yoshikawa, Teiji Uozumi, Akiko Fujimoto, Electromagnetic induction responses to geomagnetic disturbances at low-and-mid-latitudes, 1st International Conference on Space Weather and Satellite Application 2018, ICeSSAT 2018, 2019.03, The geomagnetically induced current (GIC) is one of the most widely recognized phenomena caused by geomagnetic disturbances. Realistic predictions of magnetic field fluctuations may be used to evaluate the induction of electric fields to ground surfaces, and thus to estimate the occurrence of GICs. Although many GICs occur at high latitudes, they are now being studied at low and mid-latitudes as well. The purpose of this research was to understand the dynamics, observation, and prediction in Japan for GICs occurring at the low and mid-latitudes. In this study, the influence of geomagnetic field variations on Earth's electric field was examined. The magnetic field and the electric field components of 3 observation points for 1 year in 2015 are visually examined, and the characteristics of the fluctuations of the magnetic field and the surface electrical field were also analysed..
39. T. Akiyama, Akimasa Yoshikawa, A. Fujimoto, T. Uozumi, Relationship between plasma bubble and ionospheric current, equatorial electrojet, and equatorial counter electrojet, 1st International Conference on Space Weather and Satellite Application 2018, ICeSSAT 2018, 2019.03, In recent years, it has been clarified from previous studies that plasma bubbles and equatorial electrojets (EEJs) are related. In general, EEJs are calculated by subtracting the magnetic field H component of the magnetic equator from that at low latitude. However, in this study, EE-index data at Langkawi (magnetic equator), which includes all local current systems, were used for the analysis during the period from January 1, 2011, to November 8, 2014. By using the EE-index, it was found that plasma bubbles tend to occur for larger EEJ strengths. This result differs from the previous studies. In addition, if an equatorial counter electrojet (CEJ) occurs, it is understood that plasma bubbles will rarely occur due to the westward current; however, we found that when the lunar tidal effect is strong, plasma bubbles can occur even in conjunction with CEJs. Finally, we want to find the relationship between plasma bubbles and ionospheric current to predict them..
40. Akimasa YOSHIKAWA, Research of Geomagnetism for Earth and Space Environmen, Theme Seminar of the Scientific lecture at the annual Theme Seminar of the Sri Lanka Association for the Advancement of Science (“Space Science and Technology Applications for Sustainable Development” ), 2018.12.
41. Akimasa YOSHIKAWA, Geomagnetism and Life, Geomagnetic Focus Group Discussion 2018, 2018.09.
42. Akimasa YOSHIKAWA, Space Weather Data in IR 4.0 (Industry Revolution 4.0) era and the success story on MAGDAS project, International Conference on Space Weather and Satellite Application (ICeSSAT2018), 2018.08.
43. Takafumi Akiyama and Akimasa Yoshikawa, Akiko Fujimoto, Teiji Uozumi, Relationship Between Plasma Bubble and Ionospheric Current Equatorial Electrojet and Equatorial Counter Electrojet, International Conference on Space Weather and Satellite Application (ICeSSAT2018), 2018.08.
44. Siti Nurbaiti Ibrahim, Mohamad Huzaimy Jusoh, Ahmad Asari Sulaiman, Akimasa Yoshikawa, Characteristic of the Disturbed Days Ionospheric Current System in the 180-Degree Magnetic Meridian, International Conference on Space Weather and Satellite Application (ICeSSAT2018), 2018.08.
45. Akimasa Yoshikawa, On Generalization of Birkeland Current System in the Tree-Dimensional Magnetosphere-Ionosphere Coupling, AOGS2018 15th Annual Meeting, 2018.06.
46. Teiji UOZUMI, Akimasa YOSHIKAWA, Shin OHTANI, Dmitry BAISHEV, Alexey MOISEEV, Boris SHEVTSOV, Decomposition of the Wave Elements of the Global High-Correlation Pi 2, AOGS2018 15th Annual Meeting, 2018.06.
47. Akiko FUJIMOTO, Akimasa YOSHIKAWA, Toshiya NISHIGUCHI, Local Time Characteristic of Low-Latitude Geomagnetic Field Response to Intense Solar Flares, AOGS2018 15th Annual Meeting, 2018.06.
48. Akihiro IKEDA, Teiji UOZUMI, Akimasa YOSHIKAWA, Akiko FUJIMOTO, Shuji ABE, Hiromasa NOZAWA, Manabu SHINOHARA, Response of Schumann Resonance to Solar and Geomagnetic Activities, AOGS2018 15th Annual Meeting, 2018.06.
49. A Nakamizo, A Yoshikawa, T Tanaka, Effects of Ionospheric Hall Polarization on Magnetospheric Configurations and Dynamics in Global MHD Simulation, AGU Fall Meeting, 2017.12.
50. Yoshikawa A., Monitoring of Space and Earth electromagnetic environment by MAGDAS project: Collaboration with IKIR, International Conference on Solar-Terrestrial Relations and Physics of Earthquake Precursors, 2017.09.
51. Akihiro Ikeda, Teiji Uozumi, Akimasa Yoshikawa, Akiko Fujimoto, Shuji Abe, Hiromasa Nozawa, Manabu Shinohara, Characteristics of Schumann Resonance Parameters at Kuju Station, International Conference on Solar-Terrestrial Relations and Physics of Earthquake Precursors, 2017.09.
52. Yoshikawa A., Study of Coupling Processes in the Solar-Terrestrial System, 2nd National School on EARTH and ELECTROMAGNETISM, 2017.08.
53. Yoshikawa A., Geomagnetic observation to support space weather study, AMGASA Public Talk, 2017.08, 汎世界的な地磁気多点観測網によりあぶり出される様々な宇宙天気現象、宇宙ー気象ー地象結合現象について紹介し、その適用サイエンスの幅広さと様々な地球物理現象のモニタリングの可能性について、わかりやすく講演する。.
54. Yoshikawa A., What is Space Weather?, Universidad Nacional Agraria de la Selva (UNAS) Invited Seminar, 2017.08.
55. Yoshikawa A., Recent Development of ICWSE/MAGDAS project for Study of Coupling Processes in the Solar-Terrestrial System, 日本地球惑星科学連合2017大会, 2017.05.
56. Yoshikawa A., Magnetosphere-Ionosphere coupling process produced by Ampere force forcing from the magnetosphere, 日本地球惑星科学連合2017大会, 2017.05.
57. 藤本 晶子, 吉川 顕正, 魚住 禎司, 阿部 修司, 松下 拓輝, MAGDASプロジェクトEE-indexの磁気赤道域現象への適用事例, 日本地球惑星科学連合2017大会, 2017.05.
58. 中溝 葵, 吉川 顕正, 田中 高史, Study on Effects of Ionospheric Polarization Field and Inner Boundary Conditions on Magnetospheric Dynamics and Substorm Processes in Global MHD Simulation, 日本地球惑星科学連合2017大会, 2017.05.
59. 今城 峻, 吉川 顕正, 魚住 禎司, 大谷 晋一, 中溝 葵, Application of Global Three-Dimensional Current Model for Dayside and Terminator Pi2 Pulsations, 日本地球惑星科学連合2017大会, 2017.05.
60. 秋山 鷹史, 吉川 顕正, 松下 拓輝, 藤本 晶子, 魚住 禎司, On the relationships between EEJ distribution and plasma bubble occurrences, 日本地球惑星科学連合2017大会, 2017.05.
61. 中原 美音, 松下 拓輝, 吉川 顕正, 魚住 禎司, 藤本 晶子, 阿部 修司, 磁気擾乱時における中低緯度領域電磁誘導応答の研究, 日本地球惑星科学連合2017大会, 2017.05.
62. 阿部 修司, 花田 俊也, 吉川 顕正, 平井 隆之, 河本 聡美, スペースデブリ環境推移モデルにおける大気密度モデルの改良と宇宙天気活動の影響評価, 日本地球惑星科学連合2017大会, 2017.05.
63. 津田 敏隆, 山本 衛, 橋口 浩之, 宮岡 宏, 小川 泰信, 塩川 和夫, 野澤 悟徳, 吉川 顕正, Study of the Coupled Solar-Earth System with Large Atmospheric Radars, Ground-based Observation Network and Satellite Data: Project Overview, 日本地球惑星科学連合2017大会, 2017.05.
64. Nurul Shazana Abdul Hamid, Saeed Abioye Bello, Mardina Abdullah, Akimasa Yoshikawa, The Sq-current and the Ionospheric Profile Parameters during Solar Minimum, 日本地球惑星科学連合2017大会, 2017.05.
65. Nurul Shazana Abdul Hamid, Wan Nur Izzaty Ismail, Mardina Abdullah, Akimasa Yoshikawa, Latitudinal and Longitudinal Profile of EEJ current during different phases of Solar Cycle, 日本地球惑星科学連合2017大会, 2017.05.
66. Quirino Sugon Jr., Christine Chan, Felix Muga II, Clint Bennett, Randell Teodoro, Sergio Su, Daniel McNamara, Dexter Lo, Roland Otadoy, Grace Rolusta, Akiko Fujimoto, Teiji Uozumi, and Akimasa Yoshikawa, Co-seismic magnetic signatures of Moro Gulf Quake of 2010-07-23 using MAGDAS data, 地域ネットワークによる宇宙天気の観測・教育活動に関する研究集会, 2017.03.
67. Yoshikawa A., A. Nakamizo, and S. Ohtani, Generalized Description of Three- Dimensional Magnetosphere-Ionosphere Coupling by Shear Alfvén Waves, 2016 Fall AGU Meeting, 2016.12.
68. Ohtani, S., and A. Yoshikawa, Field-aligned Currents Induced by Electrostatic Polarization at the Ionosphere: Application to the Poleward Boundary Intensification (PBI) of Auroral Emission, 2016 Fall AGU Meeting, 2016.12.
69. A. Nakamizo and A. Yoshikawa, Possibility of Ionospheric Cause of FACs and Convection Field in the Magnetosphere-Ionosphere System: The Harang Reversal, Premidnight Upward-FAC, and the Ionospheric Hall Polarization Field, 2016 Fall AGU Meeting, 2016.12.
70. Matsushita, H., A. Yoshikawa, T. Uozumi, A. Fujimoto, S. Abe, J. K. Ishitsuka, O. Veliz, D. Rosales, E. Safor and V. Beteta, Development of EEJ Model Based on Dense Ground-based Magnetometer Array, 2016 Fall AGU Meeting, 2016.12.
71. @Yoshikawa A., Magnetosphere-Ionosphere Coupling, The SCOSTEP/ISWI International School on Space Science, 2016.11.
72. Yoshikawa A., (B,V) Paradigm of Magnetosphere-Ionosphere Coupling, URSI Asia-Pacific Radio Science Conference (URSI AP-RASC 2016), 2016.08, これまでの磁気圏電離圏結合研究では、磁気圏側はMHDダイナミクス(B-Vパラダイム)で、電離圏側は静電的な電離層電流層近似(J-Eパラダイム)で扱われ、その両者は静電的な境界条件をつうじた結合問題として扱われてきた。本研究では電離圏ダイナミクスをイオン-中性大気の衝突効果により必然的に生じるHall電場を電離圏から磁気圏までシームレスに導入する理論的枠組を整理し、磁気圏電離圏結合系を一つの系のダイナミクスの下に記述する(B,V)パラダイムを提案する。これにより、これまで電気回路的な理解しかされてこなかった電離圏特有の現象をプラズマダイナミクスの文脈の下に記述することが可能となる。.
73. Impact of Space Weather on Earth COSPAR Capacity Building Workshop, Magnetosphere-Ionosphere coupling by shear Alfven wave, August 15 – 26, 2016, 2016.08.
74. Yoshikawa A., Fujimoto, A., T. Uozumi, S. Abe, H. Matsushita, and, S. Abe, Space Weather Indexes Produced by ICSWSE/MAGDAS Project, Asia Oceania Geoscience Society 13th Annual Meeting, 2016.07.
75. Matsushita, H., A. Yoshikawa, T. Uozumi, A. Fujimoto, S. Abe, J. K. Ishitsuka, O. Veliz, D. ROSALES, E. SAFOR, V. BETETA, and G. CÁRDENAS, Development Of New Eej Index By Dense Magnetometer Array In Peru, presented at Asia Oceania Geoscience Society 13th Annual Meeting, Asia Oceania Geoscience Society 13th Annual Meeting, 2016.07.
76. Fujimoto, A., T. Uozumi, S. Abe, H. Matsushita, and A. Yoshikawa, Long-term EE-index Variation for Monitoring Equatorial Electrojet Based on ICSWSE Magnetometer Network, Asia Oceania Geoscience Society 13th Annual Meeting, 2016.07.
77. Abe. S, H. Matsushita, Y. Nawata, A. Yoshikawa, Three components analysis of ground magnetometer network data for developing GIC index,13th Annual Meeting Asia Oceania Geoscience Society, Asia Oceania Geoscience Society 13th Annual Meeting, 2016.07.
78. Yoshikawa A., How much curl-free Hall current flows out to the magnetosphere as field-aligned current from Cowling channel?, Chamman Conference on Current in Geospace and Beyond, 2016.05.
79. Yoshikawa A., Shuji Abe, Teiji Uozumi, Akiko Fujimoto, Hiroki Matsushita, Hideaki Kawano, Recent development of MAGDAS project: Strategy for international alliance of geomagnetic field network observation, 日本地球惑星科学連合2016大会, 2016.05.
80. Nakamizo, A. and A. Yoshikawa, The Harang Reversal Generated by Ionospheric Polarization Field by Hall Current Divergence, 日本地球惑星科学連合2016大会, 2016.05.
81. Ohtani, S., and A. Yoshikawa, What if the evolution of auroral forms does not reflect magnetospheric processes?, 日本地球惑星科学連合2016大会, 2016.05.
82. Abe. S, H. Matsushita, Y. Nawata, A. Yoshikawa, Three components analysis of ground magnetometer network data for understanding GIC excited by space weather disturbances, 日本地球惑星科学連合2016大会, 2016.05.
83. Matsushita, H, A. Yoshikawa, T. Uozumi, J. Ishitsuka, D. Rosales, O. Veliz, V. B. Alvarado and G. M. Cárdenas, Development of dense magnetometer array in Peru for investigating detailed structure of EEJ, 1st PSTEP International Symposium, 2016.01.
84. Fujimoto, A., A. Yoshikawa, T. Uozumi, S. Abe, and H. Matsushita, Space weather environment index based on ICSWSE magnetometer network, 1st PSTEP International Symposium, 2016.01.
85. Yoshikawa A., Time-dependent generalized Ohm’s Law and formation of global Cowling channel in the ionosphere, 14th International Symposium on Equatorial Aeronomy (ISEA), 2015.10.
86. Babatunde Rabiu, O.O.Folarin, T. Uozumi, N.S.Abdul-Hamid, A.Yoshikawa, Longitudinal variation of Equatorial Electrojet and the Occurrence of its Counter Electrojet, 14th International Symposium on Equatorial Aeronomy (ISEA), 2015.10.
87. Yoshikawa A., MAGDAS Network, Space Weather, and Geomagnetic Storms, A Conference on “Scientific Frontiers: Serving the Peripheries in Times of Change”, 2015.09.
88. Yoshikawa A., Description of Magnetosphere-ionosphere coupling with Alfven waves, Olaf Amm Memorial Workshop, 2015.09.
89. Yoshikawa A., The Magnetosphere-Ionosphere Coupling, International School on Equatorial and Low-Latitude Ionosphere, ISELLI, 2015.09.
90. Imajo S., A. Yoshikawa, T. Uozumi, S. Ohtani, A. Nakamizo, P. J. Chi, Nature of dayside ionospheric current system of Pi2 Pulsations: Comparison between equivalent currents and numerical simulation, AOGS12th Annual Meeting, 2015.08.
91. Gopalswamy Nat, 吉川 顕正, 国際宇宙天気イニシアチブ プロジェクト(ISWI), 日本地球惑星科学連合2015年大会, 2015.05.
92. CHI, Peter, YOSHIKAWA, Akimasa, MANN, Ian, International collaboration in ground based magnetometer observations via ULTIMA: A tribute to Professor Kiyohumi Yumoto, 日本地球惑星科学連合2015年大会, 2015.05.
93. Akimasa Yoshikawa, ICSWSE/MAGDAS project, United Nations/Japan for Space Weather Symposium, 2015.03.
94. Estelle, Dirand, Akimasa Yoshikawa, Computer simulation on formation of ionospheric current system accompanied by the incidence of shear Alfvén waves to the ionosphere, United Nations/Japan for Space Weather Symposium, 2015.03.
95. Akimasa Yoshikawa, Hideaki Kawano, S. Abe, T. Uozumi, M. Grace, G. Maeda, ICSWSE MAGDAS project, National school on Space and Earth Electromagnetism(SEE) 2014, 2014.12.
96. Kiyohumi Yumoto, Akimasa Yoshikawa, Hideaki Kawano, S. Abe, T. Uozumi, M. Grace, G. Maeda, Recent developments from ICSWSE/MAGDAS Research Project, AGU fall meeting, 2014.12.
97. 吉川 顕正, Technical Presentation on the International Center for Space Weather Science and Education (ICSWSE) of Kyushu University, Geomagnetic Workshop in Medan (North Sumatra, Indonesia), 2014.09.
98. 吉川 顕正, Magnetosphere-Ionosphere Coupling through Alfven Wave, SCOSTEP/ISWI International Space Science School (ISSS) in Peru, SCOSTEP/ISWI International Space Science School (ISSS) in Peru, 2014.09.
99. Akimasa Yoshikawa, Hideaki Kawano, Shuji Abe, T. Uozumi, M. Grace, G. Maeda, Space Science Capacity Building at International Center for Space Weather Science and Education (ICSWSE), United Nations / Austria Symposium on “Space Science and the United Nations”, 2014.09.
100. 吉川 顕正, Theory of Cowling channel formation by reflection of shear Alfven waves from the auroral Ionosphere, AGU Chapman Conference on Low-Frequency Waves in Space Plasmas, 2014.08, Cowlingチャンネルとは電離圏に於けるHall電流が電気伝導度勾配領域において発散成分をもつことによって生じる分極電場により、2次的に励起されるHall電流によって誘導された電流系の総称であり、本来のHall電流と2次的なHall電流が同方向に流れる事により、オーロラジェット電流や、赤道ジェット電流等の強力に強調されたジェット電流効果を生み出す基本メカニズムを内包していることは良く知られている。しかしながら、このジェット電流効果を定量的にコントロールするHall電流発散の電離圏内への閉じ込め効率、Hall電流がどれくらいの割合で電離圏内に閉じ込められ、どれくらいの割合で磁気圏に沿磁力線電流として流出するのか?それによってどれくらいの強さの2次的分極電場が生成され、どの程度ジェット電流効果が生み出されるのか?という問題が理論的にも観測的にも不明なままであった。本論文では、沿磁力線電流を形成するshear Alfven waveと相互作用するHall電流系の発散部分を一意に決定する理論枠組を構築し、Hall電流の電離圏内閉じ込め効率の定式化を初めて行う事により、電離圏で最もダイナミックに変動するジェット電流系の定量的解析を可能とする道筋を示したマイルストーン的な論文である。.
101. Akimasa Yoshikawa, Technical presentation on the “International Center for Space Wather Science and Education”, Kyushu University, 第52回国連宇宙平和利用委員会, 2014.02.
102. Akimasa Yoshikawa, On formation of Global Cowling channel in the ionosphere and the generalized Ohm’s Law, AGU General Assembly 2013, 2013.12.
103. A. Nakamizo, Akimasa Yoshikawa, Shinichi Ohtani, Akimasa Ieda, Kanako Seki, Rotation of the ionospheric electric potential caused by spatial gradients of ionospheric conductivity, AGU General Assembly 2013, 2013.12.
104. G. Maeda, Akimasa Yoshikawa, S. Abe, Progress of the MAGDAS Project During 2013, AGU General Assembly 2013, 2013.12.
105. Cardinal, M.G, Akimasa Yoshikawa, Hideaki Kawano, Huixin Liu, Masakazu Watanabe, S. Abe, T. Uozumi, G. Maeda, Tohru Hada, Kiyohumi Yumoto, Capacity building activities at ICSWSE, SCOSTEP, International CAWSES-II meeting, 2013.11.
106. G. Maeda, Kiyohumi Yumoto, Hideaki Kawano, Akimasa Yoshikawa, Huixin Liu, Masakazu Watanabe, S. Abe, T. Uozumi, A. Ikeda, Cardinal, M.G, MAGDAS activities of year 2013, SCOSTEP, International CAWSES-II meeting, 2013.11.
107. S. Abe, Akimasa Yoshikawa, Hideaki Kawano, T. Uozumi, A. Ikeda, Cardinal, M.G, G. Maeda, Kiyohumi Yumoto, Rebuild of data distribution service for MAGDAS/CPMN project
, SCOSTEP, International CAWSES-II meeting, SCOSTEP, International CAWSES-II meeting, 2013.11.
108. Akimasa Yoshikawa, MAGDAS/CPMN Project, UN/Austria Symposium on “Space Weather Data, Instruments and Models: Looking Beyond the International Space Weather Initiative, 2013.09.
109. Akimasa Yoshikawa, Modeling of 3-fluid dynamic and generalized Ohm’s law for understanding ionospheric dynamics, JSPS Core-to-Core Program, 2013 ISWI and MAGDAS Africa School, 2013.09.
110. G. Maeda, Kiyohumi Yumoto, Hideaki Kawano, Akimasa Yoshikawa, A. Ikeda, T. Uozumi, Huixin Liu, S. Abe, Masakazu Watanabe, Cardinal, M.G, MAGDAS Activities in Australia Since 2005, AOGS Annual meeting, 2013.06.
111. Magdi Elfadil Yousif Suliman, 吉川 顕正, 魚住 禎司, 湯元 清文, Remotely sensed of some parameters of the solar wind via a low-latitude Pc 5 index, 2013年度日本地球惑星科学連合大会, 2013.05.
112. Akimasa Yoshikawa, State-of-art in 3D Ionosphere and internal ionospheric dynamics effect on M-I coupling, ISSI Forum "Near Earth Electro-magnetic Environment (Swarm and Cluster), 2013.04.
113. Akimasa Yoshikawa, Current Closure from Polar to Equatorial Ionosphere via Cowling Channel,, EGU General Assembly 2013, 2013.04.
114. Akimasa Yoshikawa, M-I couping theory, ECLAT Project Meeting, 2nd Project Review Graz, 2013.04.
115. Akimasa Yoshikawa, Technical presentation on the “International Center for Space Wather Science and Education”, Kyushu University, 第50回国連宇宙平和利用委員会, 2013.02.
116. Akimasa Yoshikawa, Analogy of Magnetosphere-Ionosphere coupling and Corona-chromosphere-photosphere coupling, ISSI Workshop on "Standing MHD Waves", 2013.02.
117. Akimasa Yoshikawa, Formation of Cowling channel from Polar to Equatorial Ionosphere, the 2012 AGU Fall Meeting, 2012.12.
118. Akimasa Yoshikawa, Establishment of International Center fot Space Science and education, United Nations/Ecuador Workshop on the International Space Weather Initiative (20th Workshop of the United Nations Basic Space Science Initiative), 2012.10.
119. Akimasa Yoshikawa, Extraction of polarization field and magnetospheric impedance from the M-I coupled system via shear Alfven wave, 第132回 地球電磁気・地球惑星圏学会総会・講演会, 2012.10.
120. Akimasa Yoshikawa, Aoi Nakamizo, Shin Ohtani, Teiji Uozumi, Y. Tanaka, Formation of FAC -Cowling channel connecting from polar to equatorial ionosphere, 第132回 地球電磁気・地球惑星圏学会総会・講演会, 2012.10.
121. Aoi Nakamizo, Akimasa Yoshikawa, T. Hori, A. Ieda, Y. Hiraki, K. Seiki, Y. Miyoshi, T. Kikuchi, Y. Ebihara, The Response of the Dayside Equatorial Electrojet to Step-like Changes of IMF Bz, 第132回 地球電磁気・地球惑星圏学会総会・講演会, 2012.10.
122. Run Shi, Huixin Liu, Akimasa Yoshikawa, 1D simulation of Electron acceleration by Inertial Alfven wave pulse, 第132回 地球電磁気・地球惑星圏学会総会・講演会, 2012.10.
123. Akimasa Yoshikawa, Opening of International Space Wather Science and Education, UN/Austria Symposium on Space Weather Data Analysis, 2012.09.
124. Akimasa Yoshikawa, Modeling of 3D Sq current system, JSPS Core-to-Core Program, 2012 ISWI and MAGDAS School on Space Science, 2012.09.
125. 吉川 顕正, Ryoichi Fujii, Olaf Amm, Heikki Vanhamakki, On the importance of the Cowling/polarization mechanism for the electrodynamics of the ionosphere and magnetosphere, 2012年度日本地球惑星科学連合大会, 2012.05.
126. 吉川 顕正, Shin Ohtani, 中溝葵, 魚住禎司, Kiyohumi Yumoto, 極域から磁気赤道域にかけて形成されるCowlingチャンネル, 2012年度日本地球惑星科学連合大会, 2012.05.
127. 吉川 顕正, 細川 敬祐, 小川 泰信, 電離圏に於ける入反射Alfven 波の分離, 2012年度日本地球惑星科学連合大会, 2012.05.
128. 吉川 顕正, 魚住禎司, 湯元 清文, Sq電流系に於ける3次元カウリングチャンネルモデル, 2012年度日本地球惑星科学連合大会, 2012.05.
Membership in Academic Society
  • Japan Geoscience Union
  • European Geophysical Union
  • American Geophysical Union
  • Society of Geomagnetism and Earth, Planetary and Space Sciences
Other Educational Activities
  • 2017.03.
  • 2016.04.
  • 2014.11.
  • 2011.03.
  • 2009.11.
  • 2009.04.
  • 2008.04.