太陽地球系物理コロキウム

2017年度 太陽地球系物理コロキウム

概要 宇宙空間・太陽・磁気圏・電離圏・大気圏の物理学・化学に関する新しい話題の紹介・研究発表により、この分野の学問の基礎的・包括的な理解を目的とする。
日時 毎週金曜日15:00〜
場所 理学部1号館807Aなど
参加教員 星野真弘、 関華奈子、横山央明、 天野孝伸 、笠原慧、桂華邦裕
連絡先 桂華邦裕

今後の予定(内部向け、Updated on November 27, 2017)


第26回

Date 日時 December 8, 15:00
Place 場所 Room 807, Science Bldg. 1 理学部1号館807号室
Speaker 話者 Nana Higashio
Title 題目 Energy dependence of relativistic electron variations in the outer radiation belt during the recovery phase of magnetic storms: Arase/XEP observations

Abstract 要旨を見る

The Arase satellite was launched in December 2016. The extremely high-energy electron experiments(XEP) onboard Arase measures electrons in the energy range of 400 keV – 20 MeV. After the launch, the XEP has observed variations of the relativistic electrons successfully in the inner magnetosphere. There are roughly two candidate processes of electron acceleration. The first one is the adiabatic acceleration due to the radial transport of electrons from the plasma sheet to the inner magnetosphere. Interaction with ultra-low frequency (ULF) waves are a plausible candidate to drive the radial transport. Another acceleration process is the non-adiabatic acceleration of sub-relativistic electrons to the relativistic energies in the heart of the radiation belt. The interaction with very-low frequency (VLF) waves is considered to play an important role in the internal acceleration. One of the science goals of the XEP instrument is to understand the acceleration mechanisms of the relativistic electrons.
In order to investigate the electron acceleration processes, we here focus on three geomagnetic storms occurred on March 27, April 4, and May 28, 2017, respectively. In these events, relativistic electrons in the outer belt showed a typical time variation, i.e., decrease in the main phase and then increase in the recovery phase. On one hand, the increase rates of the electrons are different between the storms. The March 27 storm, which is caused by the arrival of the high-speed coronal hole stream, accompanies a large increase of the relativistic electrons. The April 4 storm, which has a rapid Dst development and recovery, shows less acceleration and does not recover to the pre-storm level. The May 28 storm is caused by a CME and with moderate increase of the relativistic electrons especially in the small L region (L=[3,4]) . We will report on energy dependence of the increase rate and location of the relativistic electrons during the recovery phase, and their comparison between the three geomagnetic storms.

第24回

Date 日時 November 24, 15:00
Place 場所 Room 807, Science Bldg. 1 理学部1号館807号室
Speaker 話者 Yusuke Imai
Title 題目 Development of reflectron mass spectrometer for future planetary exploration

Abstract 要旨を見る

In-situ material measurement in planetary exploration is quite important in understanding origin and evolution of the planets. For the purpose of performing in-situ elemental analysis, mass spectrometers are installed, for example, on NASA’s Curiosity rover and the ESA’s Rosetta spacecraft. However, we still do not have a mass spectrometer that is suitable for the future planetary exploration. Therefore, we have decided to develop a Time Of Flight Mass Spectrometer (TOF-MS) aiming at using for the future planetary exploration. The mass spectrometer that we are developing can also be used for in-situ Potassium-Argon (K-Ar) isochron dating. The instrument for Potassium-Argon (K-Ar) isochron dating is the combination of a laser-induced breakdown spectroscopy (LIBS) for the K concentration measurement and a mass spectrometer for the Ar isotopic measurement. Considering that the instrument should be installed on a planetary lander, there exists limitation on the weight, size and power etc, it is necessary to design a small size mass spectrometer which has a mass resolution capable of the Ar isotopic measurement. In order to minimize the variation of the initial position and initial energy of the ionized ions for maximizing the mass resolution, we have decided to adopt a single-stage reflectron with two-stage acceleration part. We have analytically optimized the design parameters of the reflectron. By using SIMION charged particle simulation software we have confirmed that mass resolution of our TOF-MS is high enough for Ar isotopic measurement. We are aiming to develop the multi-reflector type TOF-MS which has the potential to increase mass resolution under the size constraint. Compared to the single-reflector TOF-MS, the flight path becomes about three times longer which makes the mass resolution of the TOF-MS improved. However, as the flight length increases, variations in the flight path of the ions increase and the detection rate decreases. In order to solve this problem, we have decided to use electron lens for reducing ion dispersion. Under the same conditions as the single-reflector TOF-MS, we confirmed improvement of mass resolution about three times as compared with the single-reflector TOF-MS.

第23回

Date 日時 November 17, 15:00
Place 場所 Room 807, Science Bldg. 1 理学部1号館807号室
Speaker 話者 Takahiro Hasegawa 長谷川 隆祥
Title 題目 Observational study of a solar flare focusing on magnetic helicity

Abstract 要旨を見る

A solar flare is the most energetic phenomenon in our solar system. The origin of energy released by flares is non-potential part of magnetic field in the solar corona. Therefore magnetic helicity, which represents complexity of magnetic field, is regarded as one of important properties of active regions and long term magnetic helicity evolution has been studied well to investigate the process of solar flares (Chae et al. 2001; Kusano et al. 2002). Some of these studies reported that magnetic helicity injection whose polarity is opposite to the global magnetic helicity has an important role on occurrences of energetic solar flares (Park et al. 2010, 2012). However, it isn’t discussed well which characteristics of magnetic field evolution the opposite magnetic helicity injection correspond to. To attack this problem, we studied the magnetic field evolution in the active region NOAA 12297 before and after an X2.1 flare. In the initial stage, the main sunspot of this region rotated in the clockwise direction. However, due to the eastward motion of the emerging flux between the sunspot and another emerging region, the sunspot started to rotate counterclockwise. This rotational motion injected the magnetic helicity opposite to the global magnetic helicity of the active region. On the other hand, average force-free α (i.e. current helicity) in the sunspot didn’t change its sign, but increased. This means the twist of the sunspot magnetic field was enhanced. Our result implies that a reversed rotation of a sunspot on the photosphere and helicity injection opposite to that of global structure have an important role for destabilization of magnetic field and an onset of solar flares.

第22回

Date 日時 November 10, 15:00
Place 場所 Room 807, Science Bldg. 1 理学部1号館807号室
Speaker 話者 Sooman Han 韓秀萬
Title 題目 A simulation study on time variability of Jupiter’s synchrotron radiation associated with solar-wind-driven electric field inferred from HISAKI

Abstract 要旨を見る

Radiation belt is a layer of energetic particles ( ̃few tens MeV) held by geomagnetic fields, ranging up to several planetary Radii in distance. Jovian Radiation Belt, where in-situ measurement is limited, Jupiter’s synchrotron radiation (JSR) observation is a main tool for determining physical process therein, and various diffusion models have been proposed to account for the observed JSR’s short-term (the total JSR flux density varies by a few % over a few days or weeks) and long-term (10-20% over a few years) variations observed in the past. In this talk, I review the the previous JSR studies and present my ongoing master thesis work based on the recent HISAKI’s finding – conclusive evidence of dawn-to-dusk electric field associated with solar wind ram pressure [Murakami et al. 2016]. From the simulation study, I suggest that a puzzling nature of long-term variation which has time lag of 2-3 years with solar wind ram pressure can quantitatively be addressed.

第20回

Date 日時 October 20, 15:00
Place 場所 Room 807, Science Bldg. 1 理学部1号館807号室
Speaker 話者 Takafumi Doi 土井崇史
Title 題目 Observational study of the formation of coronal sigmoid in the simple solar active region

Abstract 要旨を見る

The origin of solar flare has been identified as free magnetic energy accumulated in solar atmosphere. Sigmoid, which is S-shaped coronal loop seen in soft X-ray, indicates sheared and twisted coronal magnetic structure and likely to carry current and thus free magnetic energy. Thus, in order to understand formation of flare-productive active region, it is important to understand sigmoid formation. It has been shown that sigmoid formation is driven by flux convergence and cancellation between sheared arcades. This process should likely to occur in a complex active region (AR), composed of many pairs of positive and negative sunspot and statistically this is a major trend. Unlike that, there are small number of examples that sigmoid was formed even in simple AR, composed of a pair of sunspot. In the 10-year Hinode satellite observation, NOAA AR 11692 is the unique AR that is simple but sigmoidal and occurred a large scale flare. In order to comprehend the sigmoid formation in the simple AR, we have analyzed the observational data before the flare. The main results should suggest that flux cancellation occurred near the polarity inversion line until a day before the flare and there was mainly two flux ropes related to the flare.

第19回

Date 日時 October 13, 15:00
Place 場所 Room 807, Science Bldg. 1 理学部1号館807号室
Speaker 話者 Yuto Bekki 戸次宥人
Title 題目 Convective velocity suppression via the enhancement of subadiabatic layer: Role of the effective Prandtl number

Abstract 要旨を見る

It has recently been recognized that the convective velocities achieved in the current solar convection simulations might be over-estimated. The newly-revealed effects of the prevailing small-scale magnetic field within the convection zone may offer possible solutions to this problem. The small-scale magnetic fields can reduce the convective amplitude of small-scale motions through the Lorentz-force feedback, which concurrently inhibits the turbulent mixing of entropy between upflows and downflows. As a result, the effective Prandtl number may exceed unity inside the solar convection zone. In this talk, we propose and numerically confirm a possible suppression mechanism of convective velocity in the effectively high-Prandtl number regime. If the effective horizontal thermal diffusivity decreases (the Prandtl number accordingly increases), the subadiabatic layer which is formed near the base of the convection zone by continuous depositions of low entropy transported by adiabatically downflowing plumes is enhanced and extended. The global convective amplitude in the high-Prandtl thermal convection is thus reduced especially in the lower part of the convection zone via the change in the mean entropy profile which becomes more subadiabatic near the base and less superadiabatic in the bulk.

第18回

Date 日時 October 6, 15:00
Place 場所 Room 807, Science Bldg. 1 理学部1号館807号室
Speaker 話者 Takehiko Kitahara 北原岳彦
Title 題目 Stationary features at Venusian cloud top observed by Akatsuki UV Imager

Abstract 要旨を見る

Using the cloud image obtained with the Ultraviolet imager (UVI) on board the Venus orbiter Akatsuki, we detect stationary features and investigate their origin. Huge bow-shaped structures extending from northern to southern high latitudes have been discovered by the Longwave infrared camera (LIR), which is also installed in Akatsuki, and such structures have been observed several times. Since they appear above certain highlands and continue to be there against the zonal wind, they are attributed to topographic gravity waves. This study shows that there exist similar features also in other wavelengths,and we estimate the wave parameters by comparing the observed brightness variation and the result of model.

第17回

Date 日時 September 29, 15:00
Place 場所 Room 807, Science Bldg. 1 理学部1号館807号室
Speaker 話者 Lynn Kistler
Title 題目 Contributions of Oxygen to the Storm-Time Ring Current

Abstract 要旨を見る

Observations of the storm-time ring current have shown that the O+ contribution to the plasma pressure increases significantly during storms, in some cases becoming dominant during the storm main phase. This is surprising because the direct source of the ring current is the near-earth plasma sheet, and O+ is only rarely dominant there, in terms of either density or pressure. This talk will address three aspects of the oxygen in the ring current to understand how the O+ dominance occurs. First it will address whether the O+ that contributes to the ring current comes predominantly from the cusp outflow or from the nightside auroral outflow. Second, it will address how the O+ can become dominant in the inner magnetosphere, when it is usually not dominant in the plasma sheet. Finally it will address whether the high charge state oxygen from the solar wind can play a role in providing oxygen to the inner magnetosphere.

第16回

日時 9/22 15:00
場所 理学部1号館807号室
話者 Walia Nehpreet
題目 A statistical study of slow-mode shocks observed by MMS in the dayside magnetopause

要旨を見る

Petschek’s reconnection theory [1964] provides a means for faster reconnection by creating X-line geometry with two pairs of slow- mode shocks. Earth’s magnetosphere acts as a natural laboratory to investigate the presence and role of these slow-mode shocks. Considerable amount of studies have reported the presence of the slow- mode shocks in the magnetotail [e.g. Feldman et al., 1987; Saito et al., 1995; Erikson et al., 2004] but only a few have reported the slow-shocks in the magnetopause [Walthour et al., 1994; Sonnerup et al., 2016]. The slow-shocks are observed in the magnetosheath side and/or magnetosphere side of the magnetopause. These studies suggest that strong pressure anisotropy and presence of cold ions could play an important role in determining the structure of the slow-mode shocks in the magnetopause. These studies also report the presence of rotational discontinuity and theoretical studies have also indicated that the magnetopause consists of multiple MHD discontinuities [e.g., Hau and Wang, 2016]. The solar wind conditions as well as the local conditions in the magnetosphere can affect the structure of the magnetopause. One of the reasons of the small number of the slow-shock events reported for the magnetopause is the lack of the high time resolution data to separate multiple discontinuities before MMS. Thus, an exhaustive study with many events is needed to understand the underlying physics of the slow- shocks in the magnetopause.
Here we present a statistical study of slow-mode shocks in the dayside magnetopause crossings observed by MMS (Magnetospheric Multiscale). For this study, we used the data from FGM and FPI instruments onboard the MMS satellites. Fast survey data were analyzed from 1st Sept, 2015 to 31st Jan, 2017. For event selection, we checked the southward IMF magnetopause crossings with jet (|Vgsm|  200 km/s). We ensured the presence of the magnetosheath side in our events by using Plasma Beta > 1 and MA < 1 conditions. The events obtained by using this criterion were then checked by using burst mode data and incomplete magnetopause crossings were removed to get a set of 71 full crossings from the magnetosheath to the magnetosphere. Rankine-Hugoniot analysis was applied on these crossings after determining two separate deHoffmann- Teller frames for each side. Out of these 71 crossings, 23 magnetopause crossings were identified as the slow-mode shocks. Among the 23 events, 13 events contained slow-shock on the magnetosheath side whereas 10 contained slow-shock on magnetosphere side. We will report on the relation of these slow-mode shocks with solar wind conditions and the local parameters.

第15回

日時 7/21 15:00
場所 理学部1号館807号室
話者 高田雅康
題目 Differences among species in the magnetosphere and the interaction with ULF waves

要旨を見る

There are many differences among species which compose the plasma in the magnetosphere. Especially when it comes to the interaction between particles and ULF waves, they play important roles in order to understand mechanisms such as the particle acceleration process, the particle diffusion process and so on. I will talk about what have been discussed so far by introducing some basic papers on the differences after brief self-introduction and show the results of ERG data I’m focusing on now.

第14回

日時 7/14 15:00
場所 理学部1号館807号室
話者 天野孝伸
題目 In-situ signatures of whistler-electron interactions in the Earth’s
bow shock and the implication for the electron injection

要旨を見る

The acceleration of nonthermal particles is one of the most important problems in space physics and astrophysics. The standard first-order Fermi mechanism needs a seed population. It must be provided by some microscopic plasma processes occurring in the collisionless shock transition layer, which is
known as the injection problem. Recently, NASA’s MMS spacecraft with its unprecedented temporal resolution revealed the electron scale dynamics in the shock for the first time. I will discuss how the observed signatures fit into proposed theories of electron acceleration that may ultimately lead to the injection. Similarities and dissimilarities between the observations and fully kinetic particle-in-cell simulation results will also be discussed.

第12回

日時 6/30 15:00
場所 理学部1号館701号室
話者 岩本昌倫
題目 Particle Acceleration in Relativistic Magnetized Pair Shocks

要旨を見る

The origin of ultra-high-energy cosmic rays (UHECRs) is not well-understood. UHECRs are believed to be generated in active galactic nuclei (AGNs) and gamma-ray bursts (GRBs).Since the shock wave associated with the relativistic outflow form the compact central object is the common feature in these environment, Fermi acceleration is one of the most commonly proposed mechanisms for producing UHECRs. However, it is well known that the Fermi acceleration becomes less efficient in a relativistic shock propagating in a magnetized plasma. Therefore, other particle acceleration mechanism is required to explain the origin of UHECRs.
In this talk, we will show the non-thermal particle acceleration for relativistic shocks propagating in magnetized pair plasmas by using two-dimensional PIC simulation. The particle acceleration efficiency was measured as a function of the magnetization parameter. Based on this results, we discuss the non-thermal particle acceleration for astrophysical application.

第11回

日時 6/23 15:00
場所 理学部1号館807号室
話者 星野真弘
題目 Ion and Electron Acceleration during Magnetic Reconnection

要旨を見る

Magnetic reconnection receives a great deal of interest for its role in explosive magnetic energy release in many space and astrophysical phenomena such as earth’s substorms and solar flares. Not only the hot plasma production but the nonthermal high energy particle acceleration has been reported by modern satellite observations, but the strong ion acceleration events are not necessarily observed compared to the electron acceleration. PIC simulation studies have also demonstrated the high efficient electron acceleration in several key regions such as the diffusion region, the magnetic field pile-up region, and the plasma sheet boundary and so on, but the ion acceleration have not necessarily clearly demonstrated in the simulation, and is still controversial whether or not the efficient ion acceleration can occur during reconnection. We study both electron and ion accelerations in a driven reconnection system by using PIC simulations, and elucidate the high energy ion acceleration. We show in two-dimensional PIC simulation that not only the electron acceleration but also the ion acceleration can happen by injecting a finite Poynting flux from the upstream boundary. However, in three-dimensional system, the lower-hybrid-drift instability can be excited in the plasma sheet boundary, and the hot electron plasma with a flat-top velocity distribution function are generated. Therefore, the energy transfer to the electron heat occurs faster than ion, and the ion acceleration becomes less efficient compared to the electron acceleration.

第10回

日時 6/16 15:00
場所 理学部1号館807号室
話者 河野隼也
題目 MHD wave propagation and heating in the solar chromosphere

要旨を見る

The chromospheric heating is a major problem in solar physics. In the chromosphere, the dominant mechanism of energy loss is radiation. The mechanism that heats the chromosphere and maintains the temperature profile remains unclear. MHD waves, which are generated by convective motion in the photosphere, have been suggested to carry sufficient energy to the upper solar atmosphere and cause heating through wave dissipation.
In this talk, we report on our numerical works of MHD wave propagation from the convection zone to the corona. In one-dimensional MHD simulations, we calculated the transmission rate of Alfven waves from the boundaries of the chromosphere, and estimated the energy used for the chromospheric heating. We are going to extend this work to two-dimensional study and investigate the propagation of magnetoacoustic and Alfven wave modes in the solar atmosphere.

第9回

日時 6/9 15:00
場所 理学部1号館807号室
話者 三谷憲司
題目 Deeper penetrations of oxygen ions than protons into the inner magnetosphere observed by Van Allen Probes

要旨を見る

It is observationally known that protons and oxygen ions are the main components of the ring current during magnetic storms and are considered to have different source and supply mechanisms. In order to characterize the ion supply to the ring current during magnetic storms, we study the properties of energetic proton and oxygen ion phase space densities (PSDs) during the 23-25 April 2013 geomagnetic storm observed by the Van Allen Probes spacecraft. We calculated ion PSDs for specific first adiabatic invariants ( for proton; for oxygen ion) and the local pitch angles near 90 degrees. The PSD profiles as a function of L show that both proton and oxygen ions penetrated to L < 5 during the main phase of the magnetic storm. The timing of oxygen ion penetration was approximately the same for all values. The observations also show that oxygen ions penetrated more deeply in L and earlier in time than protons for the same value. We discuss the possibility that the interaction between >200 keV oxygen ions and Pc3 or Pc5 ULF waves in the inner magnetosphere causes selective transport of oxygen ions. Our results imply the importance of the contribution from >200 keV oxygen ions to the storm-time ring current.

第8回

日時 6/2 15:00
場所 理学部1号館807号室
話者 Yikang Wang
題目 Effect of radiative loss in chromosphere to spicule formation and wave propagation

要旨を見る

Radiation is one of the major tools for observing the sun. In the chromosphere, it is even more important since it is a main source of energy loss, that has a significant influence on chromosphere dynamics. While previous studies are likely to ignore radiative loss due to its difficulty, we perform 1D radiative MHD simulation and shown that the height of transition region and temperature distribution is affected by radiative loss obviously. The effect on temperature distribution also changes the Mg II line profiles. On the other hand, the energy flux transported to corona, which is crucial to coronal heating, however, is not affected decidedly.

第7回

日時 5/26 15:00
場所 理学部1号館807号室
話者 横山央明
題目 Solar chromospheric dynamics by ALMA observations

要旨を見る

From Cycle-4 of the ALMA proposal period, solar observation capability became open to the community. In the millimeter and sub-millimeter range, the solar chromosphere is a main target for studies. In this talk, we would like to describe the content of our proposal for the solar observations by using ALMA. Our team proposed an observation of chromospheric spicules; the needle-like jets ubiquitously found in the chromosphere, though their driving mechanism is still under debate. The observation has finished on late-April but, unfortunately the data is not yet delivered. So we describe what we are expecting to see based on our numerical simulations.

第6回

日時 5/19 15:00
場所 理学部1号館807号室
話者 庄田宗人
題目 High-frequency chromospheric Alfven waves generated via mode conversion

要旨を見る

Alfvenic waves propagating along spicules have high-frequency components whose typical period is around 40-50 sec. Because the typical period of photospheric oscillations is a few minutes, the origin of this high-frequency component is not trivial. Using one-dimensional numerical simulation, we show that these high-frequency waves come from longitudinal-to-transverse mode conversion occurring around the equipartition layer. Our calculation is performed in a self-consistent manner, except an additional heating that maintains coronal temperature. We show that (1) mode conversion efficiently excites high-frequency transverse waves; (2) the typical period of the high-frequency waves is explained as the sound-crossing time of the mode conversion region; (3) simulated root-mean-square velocity of high-frequency component is consistent with the observed value, respectively. Our result indicates that the observed oscillation shows high enough amplitudes if we take into account the low-frequency components.

第5回

日時 5/12 16:00
場所 理学部1号館807号室
話者 Shuoyang Wang
題目 Reconnection pattern in 3D MHD reconnection

要旨を見る

Magnetic reconnection is one of the most important fundamental processes in plasma physics. The fast magnetic energy conversion is always an interesting issue since it helps to understand many eruptive astronomical events, such as solar flares. As the classical models fail to explain the fast reconnection as observations suggested, advanced models come into view. Presently, the three-dimensional (3D) turbulence reconnection becomes a hot topic. Many studies prove that reconnection rate becomes independent on diffusivity when turbulence is highly developed, but the details for energy transfer or how the reconnection pattern changes are still not clear. In our study, we implement eigenfunctions of tearing instability to initiate reconnection in a sheared current sheet. By doing so, we could track the energy cascade in a clear way by observing the coupling between two tearing layers. We notice that the cascade primarily is by the coupling of the initial perturbed tearing layers. Then a transfer of energy is initiated along the guide field direction near the current sheet boundary on the newly convected in magnetic field. They activate new tearing instability and create new diffusion regions. On the other hand, the mode with highest energy is along the anti-parallel field at the sheet center. New diffusion regions couple with each other, which further enhances reconnection. We believe that this secondary coupling is the key to understand the final state of turbulence reconnection.

第4回

日時 4/28 15:00
場所 理学部1号館807号室
話者 高橋直子
題目 Evolution and propagation of electric fields during magnetospheric disturbances based on multiple spacecraft and ground-based observations

要旨を見る

The Earth’s magnetosphere is affected by the solar wind. The input from the solar wind leads to the global variation of the particle and electromagnetic field, which triggers magnetospheric disturbances. Among these processes, there is global evolution of electric fields, which involve the energy transmission from the solar wind and the development of large-scale convection and current systems. Thus, the evolution and propagation of electric fields is essential to understand the electromagnetic energy transmission in the magnetosphere and the magnetosphere-ionosphere (M-I) coupling system. The studies on the electromagnetic energy transmission have been performed for more than half of a century. However, there are few papers that have focused on the electric field variation due to the lack of simultaneous and multi-point in-situ measurements in the magnetosphere and ionosphere.
For the last decade, many satellites have been launched and widely distributed in the whole M-I coupling system. It can provide us a great opportunity to investigate the spatial and temporal evolution of electric fields in the magnetosphere and ionosphere. Taking advantage of this opportunity, we focus on electric field as a key parameter to clarify the electromagnetic energy transmission, and investigate the evolution and propagation processes of electric fields in the M-I coupling system. First, we deal sudden commencements (SCs) known as the phenomenon associated with the compression of the magnetosphere by the enhancement of the solar wind dynamic pressure. Unlike magnetic storms and substorms, which involve complex plasma physical processes, SCs can be identified as distinct magnetic variations that sharply change on a global scale. Those magnetic variations are caused by shock waves and discontinuity in the solar wind and propagate through the magnetosphere. From the three-dimensional evolution and propagation of electric and magnetic fields in the M-I coupling system, SCs contributes to the identification of the magnetospheric response to the outer disturbances, which is the basis to understand the whole magnetospheric reaction processes. Next, we verify whether the established evolution and propagation processes are applicable to more complex plasma physical process, such as substorms.
We investigated the following three topics:
1. Response of ionospheric electric field at mid-low latitude based on ROCSAT-1 satellite
2. Evolution and propagation of electric fields in the M-I coupled system based on multiple spacecraft (THEMIS, RBSP, GOES, and C/NOFS) and ground-based observations (SuperDARN and magnetometers)
3. Propagation of Pi2 pulsations in the M-I coupled system based on spacecraft (THEMIS and RBSP) and ground-based observations (THEMIS-ASI and magnetometers).
In December 2016, Japan Aerospace Exploration Agency (JAXA) successfully launched the Exploration of energization and Radiation in Geospace (ERG) satellite, which recently renamed ‘ARASE’, into the inner magnetosphere. Our results can contribute to one of the ARASE’s science goal of understanding how the electric field in M-I coupling system evolves and propagates during the geospace storms.

第3回

日時 4/21 15:00
場所 理学部1号館807号室
話者 成影典之
題目 Next satellite mission for the investigation of magnetic reconnection and particle acceleration

要旨を見る

We plan to realize the satellite mission for the detailed investigation of magnetic reconnection and particle acceleration. The observation target is the sun (with 5 degree offset to observe other heavenly bodies, namely, Crab Nebula). The observed wavelength is soft X-rays (0.5 – 10 keV), hard X-rays (5 – 20 keV) and soft gamma rays (up to 600 keV). For the X-ray observations, we use new observation technology as follows: In the soft X-ray observation, the imaging spectroscopic observation will be realized for the first time in the solar coronal observation using a high-speed CMOS camera. In the hard X-ray observation, we will use focusing mirrors for the higher dynamic range than the existing (modulation collimator type) hard X-ray telescope. These instruments are designed to investigate the region around the X-point, where key phenomena related to reconnection, i.e., shocks, particle acceleration, etc.,are predicted. Now, we are organizing a working group for this mission as an consortium among solar, magnetosphere, astronomy, and laboratory groups.

第2回

日時 4/14 15:00
場所 理学部1号館807号室
話者 桂華邦裕
題目 Contribution of ionospheric oxygen ions to plasma pressure in the Earth’s inner
magnetosphere: Relative importance of enhanced outflow and local acceleration

要旨を見る

Singly-charged oxygen ions, O+, which are of Earth’s atmospheric origin, are accelerated up to >100 keV in the magnetosphere. The energetic O+ population makes a significant contribution to the plasma pressure in the Earth’s inner magnetosphere in response to the arrival of solar wind structures such as coronal mass ejections and corotating interacting regions. The pressure enhancements are caused by adiabatic heating through earthward transport of source population in the plasma sheet, local acceleration in the inner magnetosphere and near-Earth plasma sheet, and/or enhanced ion supply from the topside ionosphere. Although several acceleration mechanisms and O+ supply processes have been proposed, it remains an open question what mechanism(s)/process(es) play the dominant role in O+ pressure enhancements.
In this talk, I introduce previous important observational studies and ongoing/future research on heavy ion transport and acceleration. Examples are remote-sensing observations that indicate oxygen non-adiabatic acceleration; in-situ observations that suggest adiabatic transport of pre-existing warm (100 eV to 10 keV) oxygen ions. Another study to be presented is about the long-term evolution of energetic ion energy spectra during an unexpectedly intense magnetic storm.

第1回

日時 4/7 15:00
場所 理学部1号館807号室
題目 顔合わせと趣旨説明

 

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