Software-type Wave–Particle Interaction Analyzer on board the Arase satellite

We describe the principles of the Wave–Particle Interaction Analyzer (WPIA) and the implementation of the Software-type WPIA (S-WPIA) on the Arase satellite. The WPIA is a new type of instrument for the direct and quantitative measurement of wave–particle interactions. The S-WPIA is installed on the Arase satellite as a software function running on the mission data processor. The S-WPIA on board the Arase satellite uses an electromagnetic field waveform that is measured by the waveform capture receiver of the plasma wave experiment (PWE), and the velocity vectors of electrons detected by the medium-energy particle experiment–electron analyzer (MEP-e), the high-energy electron experiment (HEP), and the extremely high-energy electron experiment (XEP). The prime objective of the S-WPIA is to measure the energy exchange between whistler-mode chorus emissions and energetic electrons in the inner magnetosphere. It is essential for the S-WPIA to synchronize instruments to a relative time accuracy better than the time period of the plasma wave oscillations. Since the typical frequency of chorus emissions in the inner magnetosphere is a few kHz, a relative time accuracy of better than 10 μs is required in order to measure the relative phase angle between the wave and velocity vectors. In the Arase satellite, a dedicated system has been developed to realize the time resolution required for inter-instrument communication. Here, both the time index distributed over all instruments through the satellite system and an S-WPIA clock signal are used, that are distributed from the PWE to the MEP-e, HEP, and XEP through a direct line, for the synchronization of instruments within a relative time accuracy of a few μs. We also estimate the number of particles required to obtain statistically significant results with the S-WPIA and the expected accumulation time by referring to the specifications of the MEP-e and assuming a count rate for each detector.

The Arase (ERG) satellite was launched on 20 December 2016 to study plasma process in the inner magnetosphere. The Magnetic field experiments (MGF), which is one of the scientific experiments onboard the Arase satellite, observes the background magnetic field and its low frequency fluctuations.
The MGF has a set of tri-axis ring-core type fluxgate sensors (MGF-S) to observe the magnetic field in the inner magnetosphere. For accurate measurements of the magnetic field vector along the Arase orbits, ground calibration experiments of MGF-S are needed.
We have been performed in order to determine the sensitivity and alignment via ground calibration experiments. From response of MGF-S to known applied magnetic field, we determined the sensitivity of each axis and found that the error of the sensitivity is less than 0.06%. The axis of the sensor is orthogonal to each other within 0.95 degrees. The estimated error of alignment is within 0.07 degrees. We also have examined the temperature dependence of the sensitivity and offset. The sensitivities relative to the room temperature have linearity with the standard error less than 0.0016, while the offset of the sensors have no clear linearity but reproducibility against temperature. From these ground examinations, the determination accuracies of the amplitude and direction of the magnetic field observed by the MGF will satisfy the science requirements for the Arase observations. In this presentation, we will also evaluate and show measurement error of MGF-S along the Arase orbit.

ERG satellite、Magnetic Filed experiment ERG satellite, Magnetic Filed experiment
The electric fields at diplarization sites in the Earth's tailside have been found to be disturbed when geomagnetic activities occurs (i.e., AL index decreases). These fields can accelerate electrons so that they are possible to be associated with electron injection or changes in electrons' pitch-angles. Therefore, it is essential to understand the variations of these environmental electric fields when dipolarization occurs. In this study, observational data of electric fields from the EFI (Electric Field Instrument) on board of THEMIS mission are analyzed. The database are selected based on dipolarization events around 10 Earth radii identified according to THEMIS observations from year of 2008 to 2011. Both the large-scale and wave-scale features of these dipolarization electric fields will be investigated. The preliminary results of this analysis will be shown in the poster.

THEMIS mission, Electric Fields, Dipolarization
Relativistic electron microbursts are short-lived bursty precipitations of relativistic electrons observed by low-altitude satellite in the radiation belt. They are considered as a consequence of pitch angle scattering of radiation belt electrons by discrete whistler-mode emissions known as chorus. Microbursts are frequently observed during geomagnetic storms and previous studies show that atmospheric loss through microbursts appears to contain enough electrons to deplete the radiation belt. They suggest that microburst is an important loss process of radiation belt electrons during the main phase of geomagnetic storms. Microbursts are also frequently observed during high-speed solar wind stream (HSS) events, while important solar wind parameters for the frequent microburst precipitations have not been well understood. We perform a superposed epoch analysis of the microburst occurrence during HSS events, considering the polarity of interplanetary magnetic field (IMF) and solar wind speed according to the method used by Miyoshi and Kataoka (2008). We find the most frequent microburst precipitations during the highest-speed solar wind streams with a southward offset of IMF (SBZ-fast HSS events), indicating that both the southward IMF and fast solar wind are important for enhanced microburst precipitations. We also demonstrate that fluxes of radiation belt electrons with energies from hundreds keV up to 7 MeV preferentially increase during the SBZ-fast HSS events. The result suggests that loss through microbursts is not major loss process of radiation belt during the HSS events. We conclude that relativistic electron microbursts can be a proxy of acceleration of MeV electrons by chorus. Interplanetary (IP) shock is known to have a large effect on the electrons trapped in the inner magnetosphere. Observations have shown that the enhancement of the electron flux depends on the pitch angle and energy. It is also proposed that when the IP shock impinges on the magnetosphere, the electrons in the radiation belts are energized not only by induced electric field but also waves excited by low-energy electrons. Therefore, we conduct simulations for acceleration processes of both energized and low-energy electrons by using the global magnetohydrodynamics(MHD) simulation and Comprehensive Inner Magnetosphere-Ionosphere Model (CIMI).In MHD simulation, 12 solar wind conditions are imposed on the upstream boundary condition by changing solar wind velocity, solar wind density and Bz of the Interplanetary magnetic field (IMF). We examine the results of response of the electron flux, temperature anisotropy, the ratio of cyclotron frequency and plasma frequency, the ratio of hot and cold electron density and cold electron density.
We obtained the simulation results as follow. 1) Generally, when the IP shock arrives, energetic electrons (>50 keV) in the dayside magnetosphere are accelerated by the sudden enhancement of the electric field associated with a compressional wave. On the nightside when southward IMF is imposed electrons are transported inward due to E×B drift because the convection electric field is developed. 2) Temperature anisotropy is increased on the nightside by the E×B drift. The value is more than 1 when southward IMF is imposed. 3) Plasmapause is slightly compressed by the compressional wave. Plasmapause is contracted by the convection electricfield when sauthward IMF is imposed. 4) The ratio of plasma frequency and cyclotron frequency is decreased because the magnetic field is increased. Relativistic electron fluxes of the outer radiation belt dynamically change in response to solar wind variations. There are several time scales for the particle acceleration in MeV energy range. One of the shortest acceleration processes is wave-particle interactions between drifting electrons and fast-mode waves induced by compression of the dayside magnetopause through interplanetary shocks (e.g., Li et al., 1993). In order to investigate how relativistic electrons are accelerated by fast-mode waves driven by solar wind pressure pulse, we perform a code-coupling simulation using the GEMSIS-RB test particle simulation (Saito et al., 2010) and the GEMSIS-GM global MHD magnetosphere simulation (Matsumoto et al., 2010).
As a case study, the interplanetary pressure pulse with the dynamic pressure of ~ 5 nPa is used as an up-stream condition. In the magnetosphere, the fast mode waves with the azimuthal electric field ( negative E phi : |E phi | ~ 10 mV/m) propagates from the dayside and then extends to the entire dayside magnetosphere from 0600 to 1800 MLT. Using the electric/magnetic fields simulated by the GEMSIS-GM, we calculate the electron motion with different initial conditions (energy, and pitch angle). As a result, the increase of electron fluxes occurs for a wide energy range and energy spectrum become hard. The acceleration depends on the initial energy of electrons. We also investigate initial pitch angle dependence of acceleration and find that the fluxes of electron whose initial pitch angle closer to 90°are largely enhanced. The pitch angle dependence may be a result of the latitudinal structure of the induced electric fields and the pich angle dependence of the drift velocity.
The results of investigation for initial energy and pitch angle imply that the acceleration condition of electrons is related to propagation speed of fast-mode waves, drift velocity of electrons and the spatial structure of electric field.  (2) Multiple energy-time dispersion appears in energy-time spectra of the ions with energy less than ~100 keV due to adiabatic acceleration at high latitudes. This is associated with bounce motion (bounce phase bunching), and consistent with the Cluster satellite observation reported by Zong et al. (2012). (3) The ion flux depends on gyro phase due to gyro phase bunching. The gyro phase bunching is prominent for ions with initial speed being comparable to, or less than the ambient ExB drift speed. These results imply that the guiding center approximation is invalid for the ring current ions when large-amplitude fast mode wave is propagating associated with the IP shock.
We also calculated temperature anisotropy. The temperature anisotropy increases near the leading edge of the wave where the dawnward electric fields is strong. The increase in the temperature anisotropy may favor the excitation of electromagnetic ion cyclotron (EMIC) waves, and may lead to rapid precipitation of ions and electrons. We evaluated growth of EMIC waves by using KUPDAP (Kyoto University Plasmas Dispersion Analysis Program). We will discuss the effect of IP shock on growing EMIC waves.

キーワード：
Keywords: Deeper and earlier penetrations of oxygen ions than protons into the inner magnetosphere observed by Van Allen Probes 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. The early penetration of oxygen ions suggest that the source of the transported oxygen ions was located closer to the Earth than the inner edge of plasma sheet protons. We also discuss the possibility that the interaction between >200 keV oxygen ions and Pc3 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.
Van Allen Probes、リングカレント、酸素イオン We statistically investigate the spatial distribution of magnetosonic waves at f < 32 Hz and proton ring-like distribution observed by Van Allen Probes from September 2012 to December 2016. The spatial distribution of magnetosonic waves has an occurrence peak at L = 4 −6 and 13 −16 MLT and that of proton ring-like distribution has an occurrence peak at L = 4 -7 and 13 -17 MLT. The coincidence of the occurrence frequency peaks suggests that proton ring-like distribution is likely to be an energy source of magnetosonic waves. We reveals that the proton ring-like distribution with V r > 2V A has potential to excite magnetosonic waves at f < 32 Hz, where V r and V A are ring velocity and Alfvén velocity, respectively. Case studies of convective growth rate analysis confirms the possibility of wave excitation by the proton ring-like distribution near the frequency of waves observed by satellites in these cases. Under the disturbed magnetospheric condition, the occurrence rate of magnetosonic waves increase up to 10 % and the ring energy increases up to ∼20 keV. This is consistent with an idea that and the high ring energy satisfies the wave growth condition of V r > 2V A . The condition of wave excitation at low frequency is attributed of a weighting function included in the calculation of the convective growth rate. A statistical analysis of the wave frequency reveals that magnetosonic waves in plasma trough are observed around the multiples of local proton cyclotron frequency except the first harmonics and most of them are considered to be excited locally, while some of magnetosonic waves observed inside the plasmapause seems to propagate from the other region.
内部磁気圏、プラズマ波動、magnetosonic waves、equatorial noise、ring like distribution、Van Allen Probes inner magnetosphere, plasma waves, magnetosonic waves, equatorial noise, ring like distribution, Van Allen Probes Nonlinear generation mechanism of EMIC falling tone emissions We have conducted a self-consistent hybrid simulation, successfully reproducing EMIC emissions with falling-tone frequencies. The hybrid simulation is implemented with a parabolic ambient magnetic field. In the simulation, strong oxygen band EMIC emissions are generated through nonlinear wave growth. The cold ion density is modulated by electrostatic structures which are induced by the forward and backward propagating oxygen band EMIC waves. Along with the growth of the oxygen band, the helium band waves also grow because of the linear growth and the nonlinear growth. The nonlinear growth of the helium band waves is affected by the cold plasma density modulation, and there appear short wave packets of helium band emissions. The short wave packets entrap energetic protons efficiently, resulting in electromagnetic proton hills in the velocity phase space. The proton hill forms a nonlinear resonant current causing the falling frequency of the EMIC waves. We find strong deformation of the velocity distribution function of the energetic protons due to the proton hill being guided by the increasing resonance velocity. are calculated using measurements of the hot (>1 keV) proton anisotropy, parallel hot proton plasma beta, the hot proton density, and the density of electrons. We examine occurrence rates and spatial distributions for the wave-favorable plasma conditions and the ratios of wave vs. non-wave occurrences under these conditions. Plasmas most favorable for EMIC wave generation are primarily observed at the probe apogee (L = ~6). Peak EMIC wave occurrence is found in the afternoon -midnight (1600 -0100) MLT sectors. This same region coincides with the enhancements of parallel hot proton plasma beta and hot proton density. Hot proton anisotropy measurements peak in the midnight -noon (0 -1200) MLT sectors.

PEM16-P17
Plasma waves and instabilities, Wave/particle interactions, Magnetospheric configuration and dynamics, Magnetosphere -inner, Ring current EMIC waves-driven radiation belt electron precipitation into the atmosphere with ground-based observations in the subauroral region Energetic electron losses from the outer radiation belt occur during magnetic storm and substorm. One of the mechanisms is precipitation into the atmosphere and electromagnetic ion cyclotron (EMIC) waves are one of candidates to cause pitch angle scattering of energetic electron. EMIC waves ,which are observed in the Pc1-Pc2 frequency range (0.1-5Hz) are excited by the ion cyclotron instability in the equatorial region of the magnetosphere during the main and the recovery phase of magnetic storms. It has been theoretically studied that EMIC waves play an important role in energetic electron precipitation into the atmosphere, but there have been limited experimental observations to support this idea.
Here, we investigated relation between occurrence of EMIC waves and energetic electron precipitation by means of ground-based magnetometers and low frequency (LF) radio wave propagation observation and confirmed EMIC waves to be driving electron precipitation. We detected energetic electron precipitation from the LF radio wave observation in 07:00-09:20 UT on July 7, 2011 and EMIC waves were observed by the induction magnetometer at Athabasca in 05:35-10:55 UT on the same day. At the almost same time, EMIC waves were observed at some CARISMA stations.
These observations indicate that EMIC waves are expected to cause detected electron precipitation.
Polarization characteristics of EMIC waves which reflect locations where the waves inject into the ionosphere and direction of subsequent horizontal propagation in the F-region were examined by cross-spectrum analysis of EMIC waves.
Based on time variations in intensity, frequency, polarization sense, and angle of the major axis, the period of EMIC appearance could be divided into six sequential events. This suggests that source of the EMIC waves observed in 05:35-10:55UT was not a single but consisted of multiple locations locations.
We found that time variation of the LF wave phase corresponds to that of EMIC waves, and the deviation of the LF wave phase only occurred during the 2nd, 3rd and 4th EMIC events. This result implies that the source locations of the three EMIC events were close to the Athabasca-WWVB radio wave propagation path and the EMIC-driven energetic electron precipitation caused the phase deviation of WWVB signal.
Identification of actual source locations of the EMIC events is a future work.  Simulation results show formation of characteristic PADs depending on the energy and location (L value), which can be explicable of the pitch angle dependence of resonance conditions. At some fixed location and energy range, the PADs can change from pancake-like to butterfly-like distributions, as the transport by the monochromatic Pc5 wave progresses. These butterfly distributions can be seen when electrons with small (oblique) pitch angles satisfy the resonance condition. It is also found that the small pitch angle electrons can be transported further inward because PA change to larger value through the adiabatic transport enables them to satisfy resonance condition in wider L range compared to the 90-degrees PA electrons. It is well known that MeV electron flux efficiently increases during the recovery phase of magnetic storms.
ULF wave propagating in the magnetosphere is recognized as one of the possible candidates which can accelerate the electron in the radiation belt while various acceleration processes have been widely proposed by many investigators.
In this study, total 20 electron flux enhancement events associated with the CIR (Corotating Interaction Region) driven storms in 2008 have been analyzed using the magnetic field vector data obtained by GOES 10 and 11 satellites. The GOES 10 and 11 were located at 60 deg. and 75 deg. West in geographical longitude, respectively, which corresponds to 1 hour separation in local time. We used the bandpass filtered (150-1000 sec) magnetic data in the ENP coordinate system to investigate the oscillation mode of the field line and the propagation characteristics of Pc5 pulsations in the GEO orbit (6.6 Re).
As a result, following features are observed, that is: both the P (compressional mode) and T (transverse mode) components of the Pc5 strongly enhances at th beginning of the electron flux decreasing in the night side sectors: the Pc5 power is relatively low at the mooning sectors: the dominant frequencies vary from high to low during the electron flux decreasing, which is quite apparent at the afternoon-night sectors. These observational facts indicates that the source region of the Pc5 during the electron flux decreasing can be considered at the evening sectors. The particle injection from night side associated with substorms may generates the ULF wave in the evening sectors. The decreasing of the dominant frequencies also suggests the particle injection from night side associated with substorms from the night to evening sectors. Landau resonance between electrons and lower-hybrid waves in the inner magnetosphere In this presentation, we discuss the Landau resonance between electrons and LH waves, by performing test particle simulation. The LH waves are given as a superposition of sinusoidal waves with different frequencies propagating highly perpendicular to the background magnetic field. The given waves obey the cold plasma dispersion relation. We evaluate the pitch-angle diffusion coefficient of electrons with energies from a few eV to 1 MeV. We discuss changes in pitch-angle distributions related to the diffusion processes.  (Nunn, 1974).
In this study, we derive the equation of the motion of particles without the assumption of small pitch angle to consider pitch angle scattering near the loss cone in the velocity phase space. We clarify that electrons near the loss cone satisfying the cyclotron resonant condition are scattered away from the loss cone due to the Lorentz force caused by the wave magnetic field and the parallel velocity component of electrons.
In order to reproduce the pitch angle scattering caused by chorus emissions, we carry out a test particle simulation using the simulation system along a dipole magnetic field line and a whistler mode wave model. Results of the test particle simulation are consistently explained by the nonlinear theory we  Pitch-angle scattering by radio waves in the VLF ( 3-30kHz) band is thought to be a major loss mechanism for energetic radiation-belt electrons. Resonant interactions with Whistler-mode VLF waves can alter the reflection altitude of trapped electrons 100keV -1MeV; when a particle reflects at a low enough altitude, it can be removed from the magnetosphere through collisions with ionospheric constituents. Terres-trial lightning provides a natural and constantly-occurring source of VLF waves. Here we present a three-dimensional forward model of lightning-induced electron precipitation (LEP) due to resonant pitch-angle scattering from a single lightning stroke.
Previous efforts (Lauben 1998, Bortnik 2006 have used two-dimensional raytracing combined with analytical expressions of pitch-angle scattering to forward model precipitation from a single stroke as a function of input and output latitude. However these models are limited in geospatial accuracy by their use of ideal plasmasphere and magnetic field models. We expand on these techniques by incorporating three-dimensional raytracing through a realistic plasmasphere and magnetic field model, to better capture the spatial dependence of LEP.
We then combine our end-to-end model of the LEP process with terrestrial lightning activity data from the GLD360 sensor network to construct a realtime geospatial model of LEP-driven energy deposition into the ionosphere. We explore global and seasonal statistics, provide precipitation estimates across a variety of magnetospheric conditions, and compare the total impact to other magnetospheric loss processes. The completed model is well-suited for comparison with satellite electron flux measurements, such as those from the Arase mission. The new wave model in the current simulation represents the sub-packet structure in its amplitude variation. Sub-packet amplitude structure is such that when the wave amplitude nonlinearly grows to reach the optimum amplitude, it starts decreasing until crossing the threshold. Once it crosses the threshold, the wave dissipates and a new wave arises to repeat the nonlinear growth and damping in the same manner. The multiple occurrence of these wave generation to dissipation processes forms a saw tooth-like amplitude variation called sub-packet. This sub-packet structure is one of the most distinctive features of chorus waves we can find from the observations and hence should be carefully included in the simulation wave model. Due to the rapid variation of amplitude sub-packet structure, however, the wave frequency as a function of amplitude also undergoes a fluctuation in time variation. This fluctuation is assumed to decrease the duration and efficiency of wave-electron resonance and resultant electron acceleration. We examine the electrons acceleration processes including RTA and URA by the sub-packets and analyze the formation mechanism of a highly energized radiation belt. First we insert 36 test particles assigned with different gyro-phases for 3 different initial energy levels: 500keV, 1MeV and 2MeV with the pitch angle of 85 degrees. The simulation results here are compared with those from the preceding study to well understand the acceleration mechanism of individual electrons. Based on this, we next conduct a statistical analysis how these accelerated electrons collectively form the outer radiation belt. We apply the Green's function method covering a sufficient number of electrons with the initial energies from 10keV to 2MeV and the initial pitch angles from 10 to 90 degrees. By the overall simulations, we reach a conclusion on how in detail the individual electron is sufficiently accelerated by the sub-packet chorus waves, and how the accelerated electrons collectively form the outer radiation belt. We perform two-dimensional electromagnetic particle simulations to study basic characteristics of whistler-mode wave particle interaction involved in chorus emissions propagating oblique to the static magnetic field.

Wave-Particle Interactions, Radiation Belts, Lightning-Induced Electron Precipitation
We assume a simple periodic (x, y) system with the magnetic field taken in the  Thus, in this study, we do a statistical analysis of substorm-associated SAR arcs observed at Athabasca.
We analyzed all-sky images at wavelengths of 630.0 nm obtained at Athabasca from 3 September, 2005 to 31 December, 2009, and found 98 events. This result indicates that the SAR arcs are often detached from the main oval after substorms at Athabasca. We investigated dependences of these SAR arc appearances and their latitudes and durations on AU/AL indices, SYM-H, X component of magnetic field variation at Yellowknife (YKC), north of Athabasca in the auroral zone, solar wind pressure, and IMF-Bz.
We found that when SAR arcs occur, AL and YKC-X component tend to decrease, indicating substorm association of these SAR arcs. We found that the SAR arc occurrence peak is around midnight with a peak rate of ~5 % with decreasing rates in both pre-midnight and post-midnight sectors. We then classified these SAR arcs into 3 types by using simultaneous 557.7-nm images as: 1) 557.7-nm images show weak structures similar to the 630.0-nm SAR arcs (30 %), 2) 557.7-nm images does not show structures similar to the 630.0-nm SAR arcs (55 %), 3) 557.7-nm images show structures different from the 630.0-nm SAR arcs (15 %). In the presentation, we will discuss possible cause of the detachment of SAR arcs from the main oval associated with substorms. The influence of the ionosphere on the aurora can be evaluated by examining the asymmetry of conjugate aurora at various time-space scales. We conducted a high-speed imaging observation of aurora at Tjornes/Iceland and Syowa/Antarctica for the time interval from 2 September 2016 to 7 September 2016 when high aurora activity continued for several days, which was driven by high-speed solar wind from a large coronal hole. It is found that an overall conjugacy is not good as we originally expected, even considering the modeled conjugate points. For example, vortex evolution from small scale (so called folds, a few ten km) to large scale (spirals, a few hundred km) occurred over whole field of view at Syowa, while such vortex structures themselves are hard to recognize at Tjornes at the same time. In this talk we discuss the conjugate morphology in more detail. Further we present the current situation and future development of the high-speed conjugate imaging observations. オーロラ、共役、高速撮像 Aurora, Conjugacy, High-speed imaging