Commission H: Waves in Plasmas (November 2013 - October 2016)
Edited by Yoshiya Kasahara (kasahara@is.t.kanazawa-u.ac.jp)
Based on the papers published from November of 2013 to October of 2016, we compiled
major achievements in the field of plasma waves and related studies made by Japanesescientists and their collaborators. We collected published papers from the JapaneseCommission H members and categorized them into three groups as shown in Contents.

Contents
H1. Space Observation and Experiment of Plasma Waves
H1.1 Magnetospheric Plasma Waves
H1.2 Lunar and Planetary Plasma Waves
H1.3 Ground Observation and Experiment of Plasma Waves
H1.4 Laboratory Experiment
H2. Theory and Computer Experiment on Plasma Waves
H2.1 Theory and Computer Experiment on Whistler-mode Chorus
H2.2 Theory and Computer Experiment on EMIC Wave
H2.3 Mode Conversion Theory in Inhomogeneous Plasma
H2.4 Other Generation Mechanisms of Plasma Waves
H3. New TechniquesH3.1 New Instruments and Sensors for Plasma Wave Experiments
H3.2 Simulation Codes and Data Analysis Systems
References Published Papers (November 2013 – October 2016)1

H1. Space Observation and Experiment of Plasma Waves
H1.1 Magnetospheric Plasma Waves<Akebono>
The Akebono was launched on February 22, 1989 and operated for 26 years. Its
observation activities were terminated on April 23, 2015, due to deterioration of onboard
instruments and reduced flight altitude after 26 years and two months of operation.
Because of its unique orbit, it achieved various observation results not only in the auroral
region but also in the radiation belt. Plasma wave instruments named VLF and PWS,
and radiation monitor (RDM) were achieved regular data acquisition for 26 years andcontributed important science output in the long-term periodical changes of the radiation
belt.
Polarization reversal and mode conversion from R-mode to L-mode (and viceversa) of the waves in ELF range are important clue to derive ion constituents in theplasmasphere. Matsuda et al. [2014a] reported EMIC waves in the vicinity of thegeomagnetic equator exhibiting a sudden decrease in intensity (characteristic lower
cutoff) at just above half of the proton cyclotron frequency. The waves were observed
during a magnetic storm in April 1989. They demonstrated that the waves propagate
with a large wave normal angle with respect to the geomagnetic field line and that they
had a crossover frequency above the characteristic lower cutoff. The waves wererepeatedly observed within a half day after sudden decreases in Dst; however, they
disappeared when the recovery of the Dst index became moderate. They suggested thatwave generation appears to be closely correlated to fresh energetic particle injection, andthat the existence of a few percent of M/Q=2 ions can explain the lower cutoff of the
EMIC waves under the condition of multiple ion species.
Ion cyclotron whistler is left-handed polarized electromagnetic ion cyclotron
mode wave converted from a lightning electron whistler. Matsuda et al. [2014b]
introduced M/Q=2 ion cyclotron whistlers observed by Akebono in the altitude region
around 3200–10000 km (L = 1.5–3.4). The observation point was a considerably higher
altitude than those previously reported, that suggests M/Q=2 ions are present not onlyin the low-altitude region but also in the inner magnetosphere around L=3.4. Following
this study, Matsuda et al. [2015] examined the spatial occurrence distributions of H+,
He+, and M/Q = 2 ion band ion cyclotron whistler waves observed by Akebono below analtitude of 10,500 km. The statistical analysis showed that H+ band ion cyclotron
whistlers are rarely observed in the equatorial region, while M/Q = 2 ion band ion
2cyclotron whistlers are frequently observed. They proposed a model for generation ofseveral bands of ion cyclotron whistlers along a propagation path. They also suggested
density enhancement process of M/Q = 2 ions in the nightside plasmasphere. This kindof ion cyclotron whistler waves are also observed by Van Allen Probes [Matsuda et al.,2016], and their specific frequencies such as cross-over frequencies and lower-hybrid
frequencies in the multicomponent ions could be important clue to derive ion constituent
in the magnetosphere and plasmasphere.
The VLF instruments on board Akebono measures not only wave spectrum indigital format but also analogue waveform, and the analogue waveform data aretransmitted via analogue telemetry. Huge amount of analogue data have been stored,
but data analyses are not comprehensively performed so far because of the difficulties of
their peculiar characteristics. Oike et al. [2014] statistically analyzed lightning whistlers
detected from the analog waveform data using a newly developed data analysis system
introduced by Kasahara et al. [2015]. Large amount of data from 1989 to 2010 were
statistically analyzed. Oike et al. [2014] demonstrated that the lightning whistlers weremainly observed inside the L shell region below 2. They also showed seasonal dependence,
diurnal variation of lightning whistlers in the plasmasphere, and comparison study withthe ground-based observation revealed consistent results considering the effects ofionosphere. Similar type of statistical study is performed by Suarjaya et al. [2016] using
narrow-band waveform receiver named Poynting Flux Analyzer (PFX). Using the PFX,
Omega signals transmitted from the ground stations were continuously observed along
the trajectories, and the detected signals are valuable for studying the propagation
characteristics of VLF waves in the ionosphere and plasmasphere.
Agapitov et al. [2014] evaluated amplitude distributions of hiss, lightninggenerated, and other whistler mode waves from terrestrial VLF transmitters obtained
from Akebono and fitted as functions of L and latitude for two geomagnetic activity
ranges (Kp<3 and Kp>3). Based on this statistics, simplified models of each wave type
are presented, and quasi-linear pitch angle and energy diffusion rates of electrons by thefull wave model are calculated.

<GEOTAIL>GEOTAIL spacecraft has been operated since 1992. The Plasma Wave
Instrument (PWI) is continuously collecting the high-resolution waveform data as wellas the spectrum data. The color plots of the spectrum data have been opened in the PWI
web site http://www.rish.kyoto-u.ac.jp/gtlpwi, and http://www.stp.isas.jaxa.jp/geotail.
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Furthermore, one can easily also make the color spectrum plots in flexible time scales in
the NICT web page http://geotail.nict.go.jp/.
Li et al. [2014] reported a sub-Alfvenic jet in the tailward outflow region near
the separatrix of the magnetic reconnection observed by GEOTAIL. Several dozens ofelectrostatic solitary waves/pulses (ESWs) were observed, respectively, on the current
sheet-side and the lobe-side of the separatrix. The ESWs on the current sheet-side are of
type-B with direction outward (toward to the tailward) while on the lobe-side they are of
type-A directed to X-line. Comparing these ESWs, they suggested that energies flowing
outward from the reconnection X-line are much larger than those flowing inward. The
observations show, that electron beams associated with ESWs are much stronger on thecurrent sheet-side than on the lobe-side of the separatrix. Furthermore, the direction of
the electron beam on the lobe-side of the separatrix is mainly antiparallel to the ambient
magnetic field and it is mainly parallel on the current sheet-side. These results are
consistent with the propagation and generation mechanisms of ESWs.
Chorus elements are generated near the magnetic equator (or the high-latitude
minimum-B pockets in the outer magnetosphere) as discrete emissions covering afrequency range of 0.1-0.65 fce0, where fce0 is the cyclotron frequency in the generation
region, with wave vectors parallel to the ambient magnetic field. Habagishi et al. [2014]
made a statistical analysis of upper band and lower band chorus emissions observed by
the GEOTAIL spacecraft. They found that the lower cutoff of the upper band emissions
coincides with 0.5 fce, while the upper cutoff of the lower band emissions represents 0.5fce0.
When 0.5fce exceeds 0.65 fce0, the chorus emission is observed as a lower band-only
emission. As the emissions propagate away from the generation region, it is possible thatthey undergo the nonlinear damping at half the local cyclotron frequency 0.5fce becauseof the quasi-parallel propagation. The nonlinear damping can separate the emissions
into the upper band and lower band chorus emissions. Since the local gyrofrequency
gradually increases away from the generation region, the upper cutoff of a lower band
element should represent half the gyrofrequency at the generation region, whereas thelower cutoff of an upper band element should follow half the local gyrofrequency. Yagitani
et al. [2014] confirmed that the frequency sweep rates and amplitudes of the observed
chorus wave packets are consistent with those predicted by the nonlinear growth theoryof chorus emissions, except for the frequency gap.
The wave modes in the ion-electron hybrid scales, such as the lower hybrid drift
wave, has been the center of attention because they enable coupling between electron
and ion dynamics and thus can be the agent for the anomalous resistivity. Shinohara etal. [2016] reported the results of a statistical survey on the wave activity in the lower4hybrid frequency range observed by GEOTAIL. They stressed the importance of thedawn-dusk asymmetry in the spatial distribution of the electric wave energy densities
that coincides with the spatial structure of the reconnection region.

<Observation by the other STP satellites>
Using the plasma wave and electron data obtained from THEMIS, Kurita et al.
[2014] showed a signature of electron pitch angle scattering driven by Electrostatic
Cyclotron Harmonic (ECH) waves in the velocity distribution function (VDF). The
diffusion curve of whistler-mode waves is used as a proxy to identify changes in VDFs
due to wave-particle interactions. They confirmed that the shape of the VDF well agrees
with the diffusion curve of whistler-mode waves when whistler mode chorus alone isactive. On the other hand, they found that the shape of the VDF deviates from thediffusion curves at low pitch angles when ECH waves are active following theinactivation of chorus waves. The result is observational support for electron pitch angle
scattering caused by ECH waves and suggests that ECH waves can contribute to
generation of diffuse auroras.
Nakamura et al. [2014] reported observations of electromagnetic ion cyclotron(EMIC) triggered emissions observed by THEMIS outside the plasmasphere. They
performed a survey of the THEMIS data and found various types of emissions mainly on
the dayside at radial distances from 6 to 10 RE. They studied three distinctive events indetail and compared these events with the nonlinear wave growth theory. They foundthat the observed relationship between the amplitudes and frequencies of the emissions
are in good agreement with the theory. Nakamura et al. [2015] investigated subpacket
structures found in EMIC rising tone emissions observed by THEMIS and showed thatthe time evolution of the observed frequency and amplitude can be reproduced
consistently by nonlinear growth theory. They also compared the observed time span ofeach subpacket structure with the theoretical trapping time for second-order cyclotron
resonance, and demonstrated that an individual subpacket is generated through anonlinear wave growth process, which excites an element in accordance with thetheoretically predicted optimum amplitude.
Nosé et al. [2014] studied magnetic fluctuations embedded in dipolarizations in
the inner magnetosphere (a geocentric distance of ≤6.6 RE) and their associated ion fluxchanges using the data from AMPTE/CCE. Seven events of depolarization, which areconsidered to be excited by the drift-driven EMIC instability, were introduced. They
perform particle tracing for H+ and O+ ions in the electromagnetic fields modeled by the5linear dispersion relation of the drift-driven EMIC instability and suggest that theelectromagnetic fluctuations associated with the dipolarizations can accelerate O+ ions
locally and nonadiabatically in the inner magnetosphere. As was demonstrated by Noséet al. [2016], magnetic field dipolarization is commonly observed in the innermagnetosphere at L=4.5-6.6. It is accompanied by strong magnetic fluctuations that havea dominant frequency close to the O+ gyrofrequency. This selective acceleration of O+
ions may play a role in enhancing the O+ energy density in the storm time ring current.
Nosé et al. [2015] studied the formation process of an oxygen torus during the
12-15 November 2012 magnetic storm, using the magnetic field and plasma wave dataobtained by Van Allen Probes. They estimate the local plasma mass density (ρL) and the
local electron number density (neL) from the resonant frequencies of standing Alfven
waves and the upper hybrid resonance band. They concluded that the oxygen torus
identified in their study favors the formation scenario of supplying O+ in the innermagnetosphere during the initial phase and subsequent drift during the recovery phase.
Using in-situ observations from the Republic of China Satellite-1 spacecraft,
Takahashi et al. [2015] investigated the time response and local time dependence of theionospheric electric field at mid-low latitudes associated with geomagnetic suddencommencements (SCs) from 1999 to 2004. The analysis supports the global instanttransmission of electric field from the polar region. In contrast, the peak time detectedin the ionospheric electric field is earlier than that of the equatorial geomagnetic field(~20 s before in the PI phase). They also showed that the electric potential distribution
is asymmetric with respect to the noon-midnight meridian, explained by the divergenceof the Hall current under non-uniform ionospheric conductivity.
Obara et al. [2016] examined a large increase of relativistic electrons in theouter radiation belt and its penetration into the inner radiation belt over slot region
using the MDS-1 satellite observations. Result of analyses demonstrates that a large
increase took place in the spring and autumn seasons, and they have newly confirmedthat the penetration of outer belt electrons to the inner radiation zone took place during
the big magnetic storms by examining a pitch angle distribution of the penetrating
electrons. They suggested that strong wave-particle interaction should take importantroles in both processes.
Parrot et al. [2015] surveyed both expected and unusual events recorded by
DEMETER when it was in operation. They showed some events are related to man-maderadio waves emitted by VLF ground-based transmitters or power line harmonic radiation.
Natural waves such as atypical quasi-periodic emissions or uncommon whistlers werealso introduced. In addition to these works, recent wave observation revealed a variety
6

of plasma wave such as compression-induced EMIC waves [Engerbretson et al., 2015],
rising-tone magnetosonic waves (MSW) [Fu et al., 2014], and fine structure ofplasmaspheric hiss [Summers et al., 2014] in the Earth’s magnetosphere.
Plasma waves generated around the plasma wake of a supersonically moving
rocket are studied by Endo et al. [2015] using data from an impedance probe and a wave
receiver installed on the sounding rocket S-520-26. During the flight of the S-520-26,
three types of plasma waves were observed: short-wavelength electrostatic waves suchas electrostatic electron cyclotron harmonic waves, upper hybrid resonance mode waves,and whistler mode waves, assuming that the observed waves are produced in the nearwake of the rocket. The wave generation mechanisms are discussed by calculating thelinear growth rates of electrostatic waves.

H1.2 Lunar and Planetary Plasma Waves<Lunar Mission>
KAGUYA was a Japanese lunar mission to explore the surface distribution ofelements and minerals, surface and subsurface structures of the moon, magnetic fieldand plasma environment around the moon. The Lunar Radar Sounder (LRS) is one of
the scientific instruments on board the KAGUYA main orbiter. The LRS consists of two
orthogonal 30 m tip-to-tip antennas and three subsystems: the sounder observation(SDR), the natural plasma wave observation (NPW), and the waveform capture (WFC).
A main objective of the SDR is to investigate the surface and subsurface structures ofthe moon using an HF radar technique, and the NPW and the WFC are passive receivers
covering the frequency ranges from 20 kHz to 30 MHz, and from 100Hz to 1MHz,
respectively.
Bando et al. [2015] investigated subsurface stratifications below Reiner Gamma,
albedo feature in Oceanus Procellarum with a high crustal magnetic field, using the
LRS/SDR. Taking into account the LRS-determined dielectric constants, the influence of
surface clutter, and the energy loss of the LRS radar pulses in the high frequency band
(5 MHz), no evidence was found of subsurface boundaries down to a depth of 1000-m at
Reiner Gamma. Given the LRS range resolution of 75-m, the source of the magnetic
anomaly is considered to be either strongly magnetized thin breccia layers at depths
shallower than 75-m, or less magnetized thick layers at depths deeper than 1000-m.
Goto et al. [2016] proposed a calibration method for wave polarization dataobtained by LRS/WFC on board KAGUYA. Thanks to the precise calibration, the7polarization data were calibrated with a sufficient accuracy. Hashimoto et al. [2015]
analyzed polarization characteristics of auroral kilometric radiation (AKR) observed by
LRS/WFC. They utilized the lunar occultation of a lunar satellite to determine the source
hemisphere of AKR, and the results are examined by ray tracing from the Earth to theMoon. This ray tracing is also applied to “banded AKR” that is observed far from the
Earth and in which emissions around 200 kHz are missing.
Narrowband whistler mode waves with frequencies near 1 Hz have been
observed near the Moon. Tsugawa et al [2014] revealed that the narrowband spectra, thefrequency concentration near 1 Hz, and the relations between the wave vector, magnetic
field vector, and sunward directions can be explained by a condition in which the groupvelocity vector is almost canceled by the solar wind velocity vector in the spacecraft frame.
Hereafter, they referred to this condition as the group-standing condition. The spectral
density is modified and has a peak at the frequency satisfying the group-standing
condition because of the difference of the frequency width between the solar wind plasma
frame and the spacecraft frame. In addition, if the waves were decelerated to be groupstanding, the conservation of the energy flux results in the intensification of the wave
amplitude at that frequency. They also derived the analytical expression of the amountof the modifications, which depend on the group velocity. These effects can explain the
narrowband spectra near 1 Hz and support the relations between the wave vector,
magnetic field vector, and sunward directions. The estimated frequency, which satisfies
the group-standing condition, is in good agreement with the observed frequency withinerror bars of the estimation. Considering the group-standing condition, they suggested
that the narrowband waves observed in the spacecraft frame are originated from oblique
whistler mode waves in the frequencies near the lower hybrid frequency, which arepossibly generated by reflected ions from the lunar magnetic anomalies.
Tsugawaetal.

[2015]

investigatedharmonic

spectralfeaturesofelectromagnetic waves identified by KAGUYA in the frequencies of several Hz aroundthe Moon. The waves have steepened waveforms peculiarly in the compressional
component. The fundamental waves have almost the same properties as narrowband
whistler-mode waves with the frequencies near 1 Hz, which have been observed aroundthe Moon. The waves are observed around the terminator region in the solar wind near
the lunar magnetic anomalies at the altitudes under 120 km. They suggested that theharmonic spectra are a result of the nonlinear steepening of narrowband whistler-mode
waves. Although the narrowband whistler-mode waves have been observed in the
upstream region of many planetary bow shocks, such harmonics have rarely been
observed there. Since the harmonics are more frequently observed at lower altitudes of8the Moon, these waves are possibly caused by lunar intrinsic environments including
lunar dusts and local structures of lunar magnetic anomalies.
Nakagawa et al. [2015] studied magnetic fluctuations in the extremely lowfrequency (ELF) range from 0.1 to 10 Hz found by the Lunar Magnetometer (LMAG) andplasma experiment (MAP) on board KAGUYA in the deepest wake behind the moon,
where the magnetic field is usually quiet. The fluctuations were compressional and nonmonochromatic, showing no preferred polarization. They were often accompanied by“type-II entry” solar wind protons that were reflected by the dayside lunar surface or
crustal magnetic field, gyrated around the solar wind magnetic field, then entered the
deepest wake. The ELF waves persisted for 30 s to several minutes. The duration wasoften shorter than that of the type-II protons. Most of the waves were detected on themagnetic field lines disconnected from the lunar surface, along which the solar windelectrons were injected into the wake. Since a large cross-field velocity difference is
expected between the type-II protons and the solar wind electrons injected along themagnetic field, some cross-field current-driven instability such as the lower hybrid twostream instability is expected to be responsible for the generation of the waves.
Low frequency waves observed in the vicinity of the moon were reviewed by
Nakagawa [2016] in association with modified distribution function of the plasma
velocity. Harada and Halekas [2016] summarized an up-to-date catalog of Moon-relatedparticle populations and lunar upstream waves obtained from in situ measurements atlow (<˜100 km) and high altitudes. It outlines the observed properties of a variety ofclasses of lunar upstream waves, as well as their generation mechanisms currently
proposed, in association with the lunar upstream particle distributions. The lunar
upstream region magnetically connected to the Moon and its wake, the fore-moon,
represents a remarkably rich zoo of different classes of waves and different types ofparticles. Although recent observations have substantially enhanced our knowledge by
revealing a number of new categories of upstream particles and waves at the Moon, many
fundamental questions remain unanswered.

<Planetary Mission>
Hisaki satellite with the EUV spectrometer (Extreme Ultraviolet Spectroscopefor Exospheric Dynamics: EXCEED) is the UV/EUV space telescope dedicated toplanetary sciences. Hisaki has provided continuous observations of Jovian system in UV
aurora total flux and EUV Io torus plasma distributions and plasma diagnostics, whichconnected the solar wind information and ground-based radio (Decameter [aurora] - VHF
9

[radiation belt]) and IR (aurora and airglows) observations. Tsuchiya et al. [2015]
analyzed the data from the EUV spectrometer continuously observed the Io plasma torus(IPT) brightness. Its variation is caused by the increase in the hot electron population in
the region downstream of Io. The longitude dependence suggests that the electron
heating process is related to the plasma density around Io. The interaction between Io
and the IPT continuously produces a large amount of energy around Io, and 140 GW ofthat energy is immediately converted to hot electron production in the IPT.
Kita et al. [2015] reported the first comprehensive observations of Jovian
synchrotron radiation (JSR) and H3+ emission from the Jovian thermosphere toinvestigate the generation process of short-term (days to weeks) variations in the Jovian
radiation belt. The observations were made by the Giant Metrewave Radio Telescope andNASA Infrared Telescope Facility during November 2011. Variations of the total JSR flux
density and thermospheric temperature seem consistent with the scenario, and thebrightness distribution of JSR can be explained by the increase in radial diffusion
accompanied by internal loss processes.
Many Japanese scientists are involved in planetary mission jointly planned by
JAXA and ESA [Kasaba et al., 2014; 2016]. BepiColombo is a Mercury exploration project.
It consists of two orbiters; the Mercury Planetary Orbiter (MPO) and the Mercury
Magnetosphere Orbiter (MMO). JAXA is responsible for development of the MMO. MMO
is at ESA/ESTEC (European Space Research and Technology Centre, Netherlands) from
April 2015. For the plasma wave, Plasma Wave Investigation is aboard this spacecraft.
JUICE (JUpiter ICy moons Explorer) is the L-class mission of ESA, planned for launch
in 2022 and arrival at Jupiter in 2030s. It will spend at least three years making detailed
observations of the Jovian system including Ganymede, Callisto and Europa, and finallybe on the orbit around Ganymede. For the plasma wave, Radio and Plasma Wave
Investigation is aboard this spacecraft and covers the information of the exospheres,
surfaces, and conducting subsurface oceans of icy satellites and their interactions withsurrounding Jovian magnetosphere. From Japan, High Frequency part (Preamp andReceiver) will be supplied, and provide the highly resolved information of Jovian
radiation emitted from Jupiter and Ganymede by the first 3-axis E-field measurement.
For the access to the conductive subsurface ocean, RPWI will first observe cold plasmaand electric fields, in order to separate the global conductivity and current from theionospheres. As a byproduct, reflected Jovian radio emission can be expected from theboundary of crust (ice) and subsurface ocean (conductive water).

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H1.3 Ground Observation and Experiment of Plasma Waves
Katoh et al. [2014] investigated the type IV burst event observed by
AMATERAS on 2011 June 7, and revealed that the main component of the burst wasemitted from the plasmoid eruption identified in the EUV images of the Solar Dynamics
Observatory (SDO)/AIA. They showed that a slowly drifting narrowband structure(SDNS) appeared in the burst’s spectra. Using statistical analysis, they revealed that
the SDNS appeared for a duration of tens to hundreds of milliseconds and had a typicalbandwidth of 3MHz. To explain the mechanism generating the SDNS, they proposed
wave-wave coupling between Langmuir waves and whistler-mode chorus emissions
generated in a post-flare loop, which were inferred from the similarities in the plasma
environments of a post-flare loop and the equatorial region of Earth’s innermagnetosphere.
Kaneda et al. [2015] investigated the polarization characteristics of a zebra
pattern (ZP) in a type-IV solar radio burst observed with AMATERAS on 2011 June 21
for the purpose of evaluating the generation processes of ZPs. The degree of circularpolarization was 50%-70% right-handed and it varied little as a function of frequency.
Cross-correlation analysis determined that the left-handed circularly polarizedcomponent was delayed by 50-70 ms relative to the right-handed component over theentire frequency range of the ZP and this delay increased with the frequency. Our results
suggest that the ZP emission was originally generated in a completely polarized state in
the O-mode and was partly converted into the X-mode near the source.
Morioka et al. [2015] studied Solar micro-type III burst storms and dipolar
magnetic field in the outer corona. In solar micro-type III radio bursts, their frequencyof occurrence with respect to radiation power is quite different from that of ordinary typeIII bursts. Micro-type III bursts occur near the edge of coronal streamers. Electron beams
are trapped along closed dipolar field lines in the outer coronal region, which arise fromthe interface region between the active region and the coronal hole. A 22-year statistical
study reveals that the apex altitude of the magnetic loop ranges from 15 to 50 R_S. The
apex altitude has a sharp upper limit around 50 R_S suggesting that an unknown but
universal condition regulates the upper boundary of the streamer dipolar field.
Shiokawa et al. [2014] reported observations of ELF/VLF chorus waves taken
by High-resolution Aurora Imaging Network (VLF-CHAIN) at subauroral latitudes at
Athabasca (L=4.3), Canada. ELF/VLF waves were measured continuously to monitor
daily variations in VLF/ELF emissions. They found quasi-periodic (QP) emissions whose
repetition period changes rapidly within a period of 1 h without corresponding magnetic
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pulsations. Falling-tone ELF/VLF emissions were also observed with their rate of
frequency change varying from 0.7 to 0.05 kHz/s over 10 min. Martinez-Calderon [2015]
calculated spectral and polarization parameters of VLF/ELF waves with high temporal
resolution using the data measured by the VLF-CHAIN. They suggest that thefrequency-dependent events, which usually last several tens of minutes, might be theconsequence of the broadening of the ray path that the waves follow from theirgeneration region to the ground. Ozaki et al. [2015b] observed a direct link between
discrete chorus elements and pulsating aurora (PA). These observations show a close
connection between chorus emissions and PA on timescales from milliseconds forgeneration of discrete chorus elements on the microphysics of wave-particle interaction
to minutes for the variations of the geomagnetic field inhomogeneity related with thesubstorm activity.
Nomura et al. [2016] studied rising tone emissions with a dispersion of 1 Hz pertens of seconds in a Pc1 on the ground. They demonstrated that pulsations of the proton
aurora have one-to-one correspondences with Pc1 rising tones, and suggested that Pc1
rising tones and associated pulsating proton auroras are due to EMIC-triggeredemissions. To understand the role of electromagnetic ion cyclotron (EMIC) waves indetermining the temporal features of pulsating proton aurora (PPA) via wave-particle
interactions at subauroral latitudes, Ozaki et al. [2016b] analyzed Pc1 pulsations thatconsisted of successive rising-tone elements with a spacing for each element of 100 s andsubpacket structures. In accordance with the temporal features of the Pc1 pulsations,the auroral intensity showed a similar repetition period of 100 s and an unpredicted fast
modulation of a few tens of seconds. These results indicate that PPA is generated by pitch
angle scattering, nonlinearly interacting with Pc1/EMIC waves at the magnetic equator.
Pulsating auroras show quasi-periodic intensity modulations caused by theprecipitation of energetic electrons of the order of tens of keV. It is expected theoreticallythat not only these electrons but also sub-relativistic/relativistic electrons precipitate
simultaneously into the ionosphere owing to whistler-mode wave–particle interactions.
Miyoshi et al. [2015] analyzed the data observed with the European Incoherent Scatter(EISCAT) Tromsø VHF radar and found electron density enhancements at altitudes >68
km in association with the pulsating aurora, suggesting precipitation of electrons with abroadband energy range from ~10 keV up to at least 200 keV. During this period, thefootprint of the Van Allen Probe-A satellite was very close to Tromsø and the satellite
observed rising tone emissions of the lower-band chorus (LBC) waves near the equatorial
plane. Considering the observed LBC waves and electrons, Miyoshi et al. [2015]
conducted a computer simulation of the wave-particle interactions, and showed12simultaneous precipitation of electrons at both tens of keV and a few hundred keV. This
result revealed that electrons with a wide energy range simultaneously precipitate into
the ionosphere in association with the pulsating aurora, providing the evidence that
pulsating auroras are caused by whistler chorus waves.
Kurita et al. [2015] reported a case in which relativistic electron precipitations
are associated with diffuse aurora based on a conjugate observation between the
SAMPEX spacecraft and the all-sky TV camera at Syowa Station. The SAMPEX
observation shows that the precipitations of > 1MeV electrons are well accompanied withthose of > 150 and > 400keV electrons. This indicates that electrons in the energy range
from several keV to > 1MeV precipitate into the atmosphere simultaneously. This result
supports the idea that whistler mode waves contribute to both generation of diffuse
auroras and relativistic electron precipitations.
Morioka et al. [2014] studied the substorm onset process on the basis of thevertical evolution of auroral acceleration regions derived from auroral kilometricradiation (AKR) spectra and Pi pulsations on the ground. The field-aligned auroral
acceleration at substorm onset demonstrated two distinct phases. Low-altitude
acceleration (h~3000–5000 km), which accompanied auroral initial brightening,prebreakup Pi2, and direct current of ultralow frequency (DC-ULF) pulsation were firstactivated and played an important role (precondition) in the subsequent substorm
expansion phase onset. Prebreakup Pi2 is suggestive of the ballooning mode wave
generation, and negative decrease in DC-ULF suggests increasing field-aligned current(FAC). They called this stage the substorm initial phase. A few minutes after this initial
phase onset, high-altitude acceleration, which accompanied auroral breakup andpoleward expansion with breakup Pi1 and Pi2 pulsations, suddenly broke out in an
altitude range from 8000 to 16,000 km. Thus, substorm expansion onset originated in
the magnetosphere-ionosphere (M-I) coupling region, i.e., substorm ignition in the M-I
coupling region. Statistical investigations revealed that about 65% of earthward flow
bursts observed in the plasma sheet were accompanied by enhanced low-altitude AKR,
suggesting that flow braking of bursts causes FAC and resulting low-altitude fieldaligned acceleration in the M-I coupling region. On the basis of these observations, they
propose a substorm onset scenario in which FAC that originated from the braking ofplasma flow bursts first enhances low-altitude acceleration (substorm initial phase
onset) and then the increasing FAC induces current-driven instability in the M-I
coupling region, which leads to high-altitude acceleration and resulting substorm
expansion phase onset.

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Teramoto et al. [2014] investigated Pi2 pulsations in the nightside ionosphereobserved with high-temporal (8 s) resolution by beam 4 of the Super Dual Auroral Radar
Network (SuperDARN) Hokkaido radar. From the radar observations and the IGRF
model, the amplitude of the eastward (EEW) component of the electric field of the Pi2
pulsations in the ionosphere was estimated ~8.0 mV/m in the F region and ~2.0 mV/m inthe E region. Corresponding Pi2 pulsations appeared dominantly in the horizontal
northward magnetic field component (H) at nearby ground stations, Moshiri (MSR), St.
Paratunka (PTK), and Stecolny (STC). At the dominant frequency of 8.8mHz, thecoherences between H and EEW were high (>0.9), the cross phases of EEW relative to H
were −56° and −45°, and the amplitude ratios were 2.7 × 105 m/s and 8.4 × 105 m/s, inthe E and F regions, respectively. Based on a comparison of these results with theoreticalpredictions, they suggested that the concept of a pure cavity mode is not sufficient to
explain the combined observations for midlatitude Pi2 waves and that the contributionof an Alfvén waves must be taken in account. Teramoto et al. [2016] studied a harmonicPi2 wave simultaneously observed by three mid-latitude Asian-Oceanian SuperDARN
radars, three THEMIS satellites, and ground-based magnetometers at low and highlatitudes. The Poynting flux derived from the electric and magnetic fields indicated thatthese pulsations were waves propagating earthward and duskward. They suggest thatcompressional waves propagate duskward away from the midnight sector, where theharmonic cavity mode is generated.
Imajo et al. [2016] statistically analyzed the longitudinal phase and amplitudestructures of Pi2 pulsations at middle- to low-latitude stations around both the dawn
and dusk terminators in order to clarify the effect of the dawn and dusk terminators on
Pi2 pulsations. Some features of the D component Pi2s depended on the location of theterminator rather than the local time. Nosé [2016] studied the long-term variations of
substorm occurrences in 1992–2015 that are evaluated with the number of Pi2
pulsations detected at the Kakioka observatory. The results suggest no clear correlation
between the substorm occurrence and the Mg II index.
Quarter-wave modes are standing shear Alfvén waves supported along
geomagnetic field lines in space. They are predicted to be generated when the ionosphere
has very different conductance between the north compared with the south ionosphere.
It was suggested that the resonant frequency is sometimes very low around the dawn
terminator due to quarter-wave modes. Obana et al. [2015] examined the resonancestructure that provides further evidence of the presence of quarter-wave modes using
the data from three magnetometers in New Zealand. These observations are strong
evidence of the presence of quarter-wave modes and mode conversion from quarter- to14

half-wave resonances. These experimental results were compared with the ULF wave
fields obtained from a 2.5-dimensional simulation model.
Sato et al. [2015] reported polarization measurement of auroral roar emissions
near 4 fce by a ground-based passive receiver in Iceland. In 9 of 11 cases, 4 fce roar was
left-handed elliptically polarized waves. The O-mode 4 fce roar was observed under bothsunlit and dark ionospheric conditions during geomagnetic storms. For O-mode 4 fce roar
generation during darkness, the condition fUH = 4 fce might be satisfied by a high-density
F region ionosphere due to auroral precipitation or tongue of ionization. In two cases,
right-handed elliptically polarized 4 fce roar was observed during darkness hours and themain phase of a geomagnetic storm. This polarization indicates that nonlinear couplingof two upper hybrid waves may also work to generate X-mode 4 fce roar. Sato et al. [2016]
reported simultaneous measurements of medium-high frequency (MF/HF) auroral radio
emissions (above 1 MHz) by ground- and satellite-based instruments. Observational data
were obtained by the ground-based passive receivers in Iceland and Svalbard, and by the
Plasma Waves and Sounder experiment (PWS) mounted on the Akebono satellite. They
found that the frequencies of the auroral roar and MF bursts detected at ground level
were different from those of the terrestrial hectometric radiation (THR) observed by the
Akebono satellite passing over the ground-based stations. This frequency difference
confirms that auroral roar and THR are generated at different altitudes across the F
peak. Space- and ground-level detections did not always accompany one another, whichwere explained as spacecraft could detect THR from wider regions while auroral radio
emissions generated in the bottomside F region were masked by ionospheric absorption
and screening in the D/E regions associated with ionization which resulted from auroralelectrons and solar UV radiation.
Tatsuta et al. [2015] studied quantitatively the effect of geomagnetic storms on
the sub-ionospheric VLF/LF propagations for different latitudes based on 2-yearnighttime data from Japanese VLF/LF observation network. Pal and Hobara [2016]
compared the amplitude of VLF signals with the atmospheric parameters (total column
Ozone (TCO) density, stratospheric temperatures etc.) for the first time for threedifferent latitudinal regions to investigate the relationship between the lower
atmosphere and upper mesosphere-lower ionosphere (UMLI) region. This study
indicates the experimental observation of latitudinal dependence of atmosphericinfluence on the upper mesosphere. Shimizu et al. [2016] analyzed lightning current
waveforms measured by a Rogowski coil installed at Mt. Ogkami and ELF waveforms
measured at Onagawa observatory. Based on comparison between the ELF and thecurrent waveforms, empirical equations for conversion from the magnetic field
15

intensities into the current intensities and charge amount were obtained. Using ELF
waveform at Kuju station in Kyushu and the Japan Lightning Detection Network(JLDN) lightning data, they newly found a clear feature showing that the time variationof charge amounts drastically changed just before the downburst onset in the Kanto
Plain.
Tsutsui [2014] detected electromagnetic (EM) waves directly excited byearthquakes in a deep borehole and confirmed them by simultaneous capturing of theirwaveforms and of seismic waves measured at the same observation site. Furthermore,
the excitation mechanism of the EM pulse was confirmed as the piezoelectric effect by alaboratory experiment, in which a seismic P-wave was readily generated by a small
stress impact, and the EM wave was simultaneously excited basically by the P-wave.
Tsutsui [2014] showed behaviors of seismic waves and of their excited EM waves whensmall and large earthquakes occurred, and that the EM waves excited by seismic waves
have leaked out of the ground surface.

H1.4 Laboratory Experiment
Two dimensional
numbermicrostructuresofquasi-perpendicular collisionless shock

a

high
and

beta
the

and

low

associatedMachparticle

acceleration process are investigated [Matsukiyo and Matsumoto, 2015]. Shoji et al.
[2016] proposed an experimental design for producing a magnetized collisionless shockby using high power laser and reported a preliminary result of the experiment using
Gekko XII laser facility at Osaka University. A high power laser experiment of aspherical shock propagating in an external magnetic field was performed [Kuramitsu etal., 2016a] and electron density, electron and ion temperatures, charge state, and drift
velocity of the plasma jet were measured by collective Thomson scattering measurement[Ishikawa et al., 2016]. Matsukiyo et al. [2016] investigated collective Thomson
scattering of a monochromatic laser light in non-equilibrium plasmas, which may occur
in the vicinity of a collisionless shock. Kuramitsu et al. [2016b] reported experimental
results on Kelvin-Helmholtz (KH) instability and the associated vortices in laserproduced plasmas.

16H2. Theory and Computer Experiment on Plasma Waves
H2.1 Theory and Computer Experiment on Whistler-mode Chorus
Study on wave-particle interaction occurring in the magnetosphere arevigorously performed combining with simulations and observations to clarify generation
mechanisms of plasma waves such as chorus and EMIC as well as particle scatteringand acceleration. Particle precipitation into the atmosphere is believed to be one of thedominant mechanisms for the loss of energetic electrons from the Van Allen radiation
belts. Wave-particle interactions involving ULF through to VLF waves are thought to beimportant drivers of these loss events. There is growing interest in energetic electron
precipitation (EEP). Much of the renewed interest comes from NASA’s recent Van Allen
Probes mission, which has stimulated new experimental and theoretical research andopened up new understanding into the fundamental physical processes of radiation-belt
dynamics [Rodger et al., 2014].
Omura [2014] gave a brief account of the nonlinear theory of the generation
mechanism of chorus emissions. The nonlinear dynamics of resonant electrons, and theformation of the electromagnetic electron “hole” that results in resonant currents
generating rising-tone emissions are introduced. In contrast, falling-tone emissions are
generated through the formation of electron “hills.” The mechanism of nonlinear wave
damping due to quasi-oblique propagation, which results in the formation of a gap athalf the electron cyclotron frequency, is also described.
Omura et al. [2015a] showed a nonlinear theory of chorus waves to explain
observations of coherent hiss emissions. They derived optimum wave amplitudes fortriggering rising and falling tone emissions and demonstrated that upper limit of hiss isdetermined by optimum and threshold amplitudes for rising tones. Omura et al. [2015b]
proposed a formation process of relativistic electron flux through interaction with chorus
emissions. They demonstrated that chorus emissions can accelerate electrons from tensof keV to several MeV within a few minutes, and a dumbbell distribution of relativistic
electrons is formed by nonlinear trapping (RTA + URA). Finally, a numerical Green’s
function method for chorus wave-particle interaction is formulated.
Nunn and Omura [2015] investigated nonlinear wave-particle interaction in
oblique whistlers in the Earth's magnetosphere. They derived relativistic electron
equations of motion for oblique whistlers and the resonant particle distribution function,
resonant current, and nonlinear growth rate are computed.

17

Katoh [2014] studied the propagation of whistler-mode chorus in themagnetosphere by a spatially two-dimensional simulation code in the dipole coordinates.
The simulation system was set so as to assume the outside of the plasmapause,
corresponding to the radial distance from 3.9 to 4.1 RE in the equatorial plane and thelatitudinal range from −15° to +15°. A model chorus element is assumed to propagate
northward from the magnetic equator at L=4 with a rising tone from 0.2 to 0.7 fce0. The
simulation results showed that resultant wave spectra observed along the field line aredifferent between the density enhancement and density decrease duct cases. This study
clarifies that the variation of propagation properties of chorus should be taken into
account for the thorough understanding of resonant interactions of chorus with energetic
electrons in the inner magnetosphere.
Katoh and Omura [2016] carried out a self-consistent simulation of thegeneration process of whistler-mode chorus by a spatially one-dimensional electron
hybrid code, by assuming the magnetic field inhomogeneity corresponding to L=4 of thedipole field. They demonstrated that spectral fine structures found in simulation results
were similar with the observation by the Cluster spacecraft. But the gap at half the
gyrofrequency was not found in simulation results. That implies oblique propagation of
the waves with respect to magnetic field, which cannot be treated in one-dimensional
simulations, are essential for forming the half gyrofrequency gap.

H2.2 Theory and Computer Experiment on EMIC Wave
Shoji and Omura [2014] performed parametric analyses of electromagnetic ion
cyclotron (EMIC) triggered emissions with a gradient of the nonuniform ambient
magnetic field using a hybrid simulation. According to nonlinear wave growth theory, as
the gradient of the ambient magnetic field becomes larger, the theoretical threshold of
the wave amplitude becomes larger, although the optimum wave amplitude for nonlinear
wave growth does not change. With a larger magnetic field gradient, they obtained
coherent rising-tone spectra because the triggering process of the EMIC triggeredemission takes place only under a limited condition on the wave amplitude. On the other
hand, with a smaller magnetic field gradient, triggering of the emissions can be causedwith various wave amplitudes, and then the subpackets are generated at various
locations at the same time. The concurrent triggering of emissions results in incoherent
waves, observed as “broadband” EMIC bursts.

18

Kubota et al. [2015] performed test particle simulations of relativistic electronsinteracting with EMIC-triggered emissions in the plasmasphere. They found thatelectrons are guided to lower pitch angles by nonlinear trapping and precipitation ismodulated by the subpacket wave periods. They concluded that electrons at 0.5-6 MeV
are precipitated efficiently by EMIC-triggered emissions.

H2.3 Mode Conversion Theory in Inhomogeneous Plasma
Kalaee and Katoh [2014] investigated the effect of the spatial scale of thedensity gradient on the mode conversion efficiency in an inhomogeneous plasma where
the mode conversion can occur only by the tunneling effect. For a particular angle ofincidence wave, it is possible for a slow Z-mode wave incident on an inhomogeneous
plasma slab to be converted into an LO mode wave. For another wave normal angle ofthe incident wave, however, it has been considered impossible, since an evanescenceregion exists between two mode branches. By considering the steepness of the density
gradient, their simulation results show the efficient mode conversion could be expectedeven in the case that the mismatch of the refractive indexes prevents the close couplingof plasma waves. They also showed the cases the beaming angle does not correspond to
Jones’ formula. This effect leads to the angles larger and smaller than the angle
estimated by the formula. This type of mode conversion process becomes important in acase where the different plasmas form a discontinuity at their contact boundary.
Recent spacecraft's observations of kilometric continuum radiation showed thatthe observed beaming angle of radiations often deviates from the prediction of the linear
mode conversion theory (LMCT). Satellite observations also show some local fluctuationin the density gradient. Kalaee et al. [2014] considered the mode conversion process from
UHR- mode (slow Z- mode) to LO-mode (ordinary) waves, focusing on the effect of theangle between the density gradient and the external magnetic field on the efficiency of
the LMCT and the resultant beaming angle of converted LO-mode waves. From theresults of analyses, for both perpendicular and oblique cases, the highest conversion
efficiency is obtained for a certain value of the wave normal angle (critical wave normal
angle) of the incident slow Z-mode waves, corresponding to the case when two mode
branches are matched. The simulation results show in the perpendicular case that thebeaming angle is consistent with the conventional LMCT; but in the oblique case acritical wave normal angle becomes different from the perpendicular case and thebeaming angle is different from the LMCT prediction.
19

Kalaee and Katoh [2016a] studied a condition required for mode conversion ofelectrostatic waves propagating purely perpendicular to the ambient magnetic field, by
numerically solving the full dispersion relation. Numerical calculation revealed that theangle between the boundary surface and the magnetic field vector should be within a
specific range in mode conversion processes in inhomogeneous plasma, which imply thatthe angle between the magnetic field and the density gradient plays an important rolein the conversion process. The effect of the angle between the magnetic field and gradientdensity on beaming angle of mode conversion process was also investigated by Kalaee
and Katoh [2016b]. The calculated beaming angle in this study was consistent with
continuum radiation events, which are observed by CRESS and IMAGE.

H2.4 Other Generation Mechanisms of Plasma Waves
Kakad et al. [2014] performed both fluid and particle-in-cell (PIC) simulationsof ion acoustic solitary waves (IASWs) and estimated the quantitative differences in theircharacteristics like speed, amplitude, and width. They found that the number of trappedelectrons in the wave potential is higher for the IASW, which are generated by largeamplitude initial density perturbation (IDP). The present fluid and PIC simulation
results are in close agreement for small amplitude IDPs, whereas for large IDPs theyshow discrepancy in the amplitude, width, and speed of the IASW, which is attributed tonegligence of kinetic effects in the former approach.
Lee et al. [2014] presented a brief review of wave generation via the cyclotron
maser instability by an electron ring distribution, and the associated electron
acceleration by the excited Z-mode and whistler-mode waves. The electron ring
distribution can excite X-mode waves mainly in the perpendicular direction, Z-mode
waves in the perpendicular and parallel directions, and whistler-mode waves in theparallel direction.

20

H3. New techniquesH3.1 New Instruments and Sensors for Plasma Wave Experiments
It is very important to develop new instruments that are highly miniaturized
and lightweight for multipoint observations using small satellites in the Earth’s
magnetosphere as well as planetary missions [Saito et al., 2014].
Koyanagi et al. [2014] examined the strength and long-term durability of a spinaxis extensible rigid antenna element, made of tri-axial woven carbon fiber-reinforced
polymer (CFRP), for a spinning spacecraft. Due to a slight deviation between the spin
axis and antenna-extended axis with the spin, the antenna is subjected to centrifugal
body force; the centrifugal force enhances the antenna deflection. A relationship between
centrifugal force and antenna deflection is derived from beam theory. As the apparent
material modulus decreases with time, the deflection increases simultaneously. The timedependence of mechanical properties of the tri-axial woven CFRP is hence examined bya creep test. The time-dependent failure criterion of the antenna is then examined using
a flexural durability test. Based on the beam theory and experimental results, theyexamined the long-term reliability of applying the tri-axial woven CFRP to extensible
rigid antenna for the spinning spacecraft, especially for SCOPE mission; it was verified
that the current design tolerance for the mission assures certain durability for long-term
usage.
In order to considerably reduce circuit resources (mass, volume, and power) for
the analog front ends of plasma wave measurement systems, Ozaki et al. [2014] designed
a current-sensitive preamplifier for magnetic search coils (MSCs) with standard 0.25μm complementary metal-oxide-semiconductor (CMOS) technology. Since the input noise
current determines the output noise levels around the resonant frequency of an MSC, a
CMOS preamplifier operating with low noise current is suitable when combined with an
MSC instead of using bipolar junction transistors. A prototype of the CMOS preamplifier
was fabricated on a 1.9×3.3-mm2-silicon chip. The noise equivalent magnetic inductionof the CMOS preamplifier combined with a 100-mm-long MSC is 3.5 pT/Hz1/2 at 10 Hz
and 30 fT/Hz1/2 at 2 kHz with a power consumption of 4.6 mW for a 3.3-V supply.
Following this technique, Ozaki et al. [2016a] developed a preamplifier for the 3-axis
loop antenna of an electromagnetic sensor probe by using application-specific integrated
circuit (ASIC) technology with a 0.25-μm complementary metal-oxide-semiconductor
process.

21

On the other hand, Ozaki et al. [2015a] developed an equivalent circuit modelfor the electric field sensitivity of a magnetic search coil (MSC) in a collisionless isotropic
cold plasma. MSCs are sensitive to both magnetic and electric fields, but detecting
electric fields is unnecessary for magnetic observations of plasma waves. It is importantto evaluate both sensitivities for different geometries and electrostatic shields to avoid
electric field pickup. The electric field sensitivity is defined by a relationship between
the MSC impedance and the sheath capacitance. To confirm the validity of the circuit
model, the sensitivity to an electric field was measured by imposing an external electricfield using charged parallel metallic plates in laboratory experiments. The coupling
capacitance between the MSC and charged plates is equivalent to the sheath capacitancein a space plasma. The measured results showed good agreement with an approximate
expression deduced from the equivalent circuit model. This agreement supports thevalidity of the proposed equivalent circuit model. An electrostatic shield having slits isoften used to reduce eddy current losses in the shield. It has been found, however, thatsuch slits result in a deterioration of the electric field sensitivity by exposing a part ofthe sensor coil to the plasma sheath. These results will be useful in evaluating theelectric field sensitivity of an MSC covered by an electrostatic shield.
Miyake et al. [2015] developed 3D particle-in-cell simulations including longand extremely thin wire booms as well as a spacecraft chassis, and investigated anelectrostatic environment. Even subsonic ion flows can produce an appreciable potential
difference between the upstream and downstream sides of the spacecraft, and thepotential difference would be detected as a spurious field of a few mV/m. The necessary
condition for the spurious field is a relatively high (a few tens of V) spacecraft potential,
and also the spacecraft potential hump needs to be expanded by thin wire booms biased
at the spacecraft potential. The analysis also reveals that the presence of a heavy ion
flow and a field-aligned ion upflow can further enhance the spurious field up to 5 mV/m.

H3.2 Development of Simulation Codes and Data Analysis Systems
Kitahara and Katoh [2016] proposed a new method to detect pitch angle
scattering caused by plasma waves and evaluated the feasibility of the proposed method
using the simulation data. The proposed method enables us to identify the location where
pitch angle scattering occurs. It can be applied to the results of space-based observations
by the forthcoming ERG satellite.

22

Katoh et al. [2016] developed a spatially one-dimensional electron hybrid code
domain-decomposed by OhHelp, a library for PIC simulation with achieving bothdynamic load balancing and scalability for the study of the generation process ofwhistler-mode chorus emissions and relativistic electron acceleration in the Earth's
inner magnetosphere. They evaluated the efficiency and scalability of the developed codetested on the system A (Cray XE6) of Academic Center for Computing and Media Studies,
Kyoto University.
Sugiyama et al. [2015] studied EMIC wave instabilities in a kappa-Maxwellian
and showed characteristics of higher harmonics of EMIC waves. Technical description of
KUPDAP dispersion solver is also given.
Wave distribution function (WDF) method is one of most sophisticated direction
finding techniques based on the idea that observed signals consist of a number of
elementary plane waves that define wave energy density distribution. However, theresulting equations constitute an ill-posed problem in which a solution is not determineduniquely; hence, an adequate model must be assumed for a solution. Ota et al. [2015]
proposed a new method for direction finding of the plasma waves measured by plasma
wave receivers. Their method is based on the assumption that the WDF can be
represented by a Markov random field model with inference of model parameters
performed using a variational Bayesian learning algorithm. Using computer-generated
spectral matrices, they evaluated the performance of the model and compared the resultswith those obtained from two conventional methods.
A variety of satellite missions, Earth observations and environments, Space
physics and Astrophysics and Commercial uses, are carried out every year. Most of thesatellites yield a large-scale data, and high-performance data processing technologies
are expected. Murata et al. [2013a] developed a cloud system (the NICT Science Cloud)for big data analyses of Earth and Space observations via spacecraft. They proposed a
new technique to process large-scale data with paying attention to the fact that highspeed I/O (data file read and write) is important compared with data processing itself.
They also adopt a task scheduler, the Pwrake, for easy management of parallel dataprocessing. Many functions are expected to the science cloud; such as data
standardization, data collection and crawling, large and distributed data storage system,
security and reliability, database and meta-database, data stewardship, long-term data
preservation, data rescue and preservation, data mining, parallel processing and so on.,data publication and provision , semantic web, 3D and 4D visualization, out-reach andin-reach, and capacity buildings [Murata et al. 2013c; Watanabe et al., 2014a; Murata et23

al., 2014a; 2014b]. Due to rapid increase of network bandwidth in recent years, Watanabe
et al. [2016] discussed a distributed file system for high performance computing to store
large-scale data such as plasma simulations or observations. They developed a toolworking in long fat networks (LFNs) between Japan and USA with its latency (RTT:
round trip time) of 152ms and throughput of 7Gbps in reading and 5Gbps in writing.
Many applications were performed on the NICT Science Cloud for theevaluation of the system and for practical use. It is pointed out that research
environment for circulation and utilization of observation data in many research fields,
including the Solar-Terrestrial Physics (STP), is not sufficient because the data formats
of observation data are not common. To overcome this problem, a database systemdesigned for Linked Open Data and Semantic Web was proposed by Murata et al. [2013b].
Using a set of long-time scientific satellite observation data (GEOTAIL satellite),
Murata et al. [2014c] examined the performance of the system on the NICT Science
Cloud. They successfully archived high-speed data processing more than 100 times fasterthan those on traditional data processing environments. The 3D phased array radar
equipped in the Osaka University of Japan rotates in 30 seconds to capture a 3D
structure of (strong) rain within 60km in radius and 15km in altitude. Watanabe et al.
[2014b] succeeded in developing a real-time 3D visualization system which enables todraw the 3D animation of rain structure (51MB/step) at a remote client computer ofTokyo within 70 seconds after every rotation. In order to realize the concept of the World
Data System (WDS), Murata et al. [2014e] proposed a Web application forinterdisciplinary researches working on the NICT Science Cloud. Based on our design ofthe Web with help of HTML5 and Ajax technologies, we implemented a Web using acouple of mission datasets. Data plots are previewed on the Web application with higher
usability than traditional data plot tools. Kubota et al. [2014] developed a system of
Magnetic Field Tracing in Global MHD simulations in order to understandmagnetosphere convection. To trace magnetic flux tube with high precision, they
introduced a parallel distribution visualization technique for magnetic field tracing byusing NICT science cloud. Yagi et al. [2015] analyzed a set of waveform data measured
by the WFC-L receiver on board KAGUYA importing their original program, without
rewriting, on the NICT science cloud. They demonstrated that easy task scheduling andparallel processing is effective and practical for big data analysis even in case that thedata set is heterogeneous. The results of research works using the cloud system are also
summarized in Murata et al. [2014d] focusing on how we effectively take advantage of acloud system on research works in various fields.

24

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