COMMISSION H: Waves in Plasmas (November 2004 – October 2007)
Edited by Toshimi Okada and Yoshiharu Omura

Based on the papers published from November of 2004 to October of 2007, we compiled
major achievements in the field of plasma waves and related studies made by Japanese scientists
and their collaborators. We categorize the studies into three groups as shown in Contents. Eachsection provides a specific summary of important scientific achievements rather than acomprehensive report of the whole research activities of Japanese Commission H. On the other
hand, the reference list attached at the end is intended to be used as a database of all papers wehave collected from the Japanese Commission H members.
Contents
H1. Space Observation and Experiment of Plasma Waves
H1.1 Magnetospheric Plasma Waves< AKEBONO, GEOTAIL and related Satellite >< Jovian Radio Emission >H1.2 Ionospheric Radio Waves< Rocket Experiment >H1.3 Ground Observation and Experiment of Plasma Waves< Solar Radio Burst >< ULF Wave >< Polar Region Experiment >< Sub-Ionospheric Radio Waves including Seismic and Lightning Emissions >H2. Theory and Computer Experiment on Plasma Waves
H2.1 Wave Propagation and Wave-Particle Interaction
H2.2 Antenna in Space Plasma
H3. New Projects for Lunar and Planetary Plasma Wave Study< KAGUYA >< BepiColombo >< ERG >
< Jupiter Mission >References
Acknowledgement
H1. Space Observation and Experiment of Plasma Waves
H1.1 Magnetospheric Plasma Waves<AKEBONO , GEOTAIL and related Satellite>
Nineteen years has past since Akebono was launched in 1989. The instruments onboard
Akebono is still successfully working and enormous dataset has been stored. The total amountof the digital (PCM) data is about 2 tera-bytes, and the analogue data will amount to 20
tera-bytes if we digitize all of them, which are recorded in 20,000 tapes of DAT. In order tomanage the huge datasets effectively, a database system on the VLF/ELF waves observed by
Akebono is now under construction [Takata et al., 2006; 2007].
Goto et al., [2004] introduced an inversion technique to estimate electron density profile in
the plasmasphere based on the propagation characteristics of whistler mode wave. As lightning
whistlers were frequently observed by the wideband receiver (WBA) onboard Akebono, thistechnique is a quite useful method not only for scientific interests but also for engineering
applications since the plasmaspheric plasma cannot be ignored for high-precision navigationand positioning from artificial satellites [Goto et al, 2006].
Kasahara et al. [2004] have studied chorus emissions observed by Akebono in the vicinity ofthe outer radiation belt associated with magnetic storms. They estimated the energies of whistler
mode wave and relativistic electrons during recovery phase of magnetic storms, and the totalenergy of chorus generated during magnetic storm is large enough to accelerate relativistic
electrons.
Miyoshi et al. [2007] studied evolution of energetic electron fluxes, related solar windconditions, and relevant plasma waves in the inner magnetosphere during the two corotatinginteraction region (CIR)-driven magnetic storms in November 1993. They reported that the fluxof the outer radiation belt electrons increased significantly during the 3 November storm, while
it did not increase above the prestorm level during the 18 November storm. They concluded thatthese differences can be related to the southward offset of interplanetary magnetic field (IMF) inthe high-speed coronal hole stream, which is influenced by the IMF sector polarity via the
Russell-McPherron effect.
Kumamoto et al. [2004] investigated long-term variations of ambient electron number density
in the nightside auroral region based on auroral hiss data observed by the PWS. The electron
number density in the nightside auroral region shows clear dependence on solar activity.
Morioka et al. [2007] identified two sources of auroral kilometric radiation (AKR) and theirdevelopment prior to and during substorms. One source is a low-altitude source region
corresponding to middle-frequency AKR and the other is a high-altitude source region
corresponding to low-frequency AKR.
Seasonal and solar cycle dependences of the correlation between auroral kilometric radiation(AKR) and the auroral electrojet (AE) index have been investigated based on the plasma wave
data obtained by the Akebono satellite [Kumamoto et al., 2005, 2006]. AKR power flux
increases as about the 1.2 power of AE index in all seasonal and solar activity conditions.
However, even for the same AE index, AKR power flux during solar minimum is 5 dB larger
than that during solar maximum.
The behavior of AKR during magnetically quiet periods is investigated by Morioka et al.
[2005a]. Features of quiet-time AKR indicated that the onset of AKR is one of the elementarycomponents of the contracted substorm. Unexpected features showing that AKR spectra do notalways depend on the substorm magnitude are also presented.
Seki et al. [2005] presented a paper concerning the magnetosphere-ionosphere coupling (M-I
coupling) process in the upward field aligned region during magnetic storm, using AKR
observations. The paper found that the auroral precipitation during the main phase of magnetic
storms is not characterized by the inverted-V type electron precipitation but by the Maxwellian
type precipitation, indicating the missing of the field aligned potential in the M-I couplingregion during the main phase.
LHR band emissions observed at mid-latitude were investigated using data from the EXOS-C(Ohzora) satellite by Morioka et al. [2005b]. The results are, (1) LHR propagates in the LHR
duct formed horizontally in the mid-latitude upper-ionosphere, (2) The emission is closely
related to the occurrence of ionospheric ELF hiss, and (3) LHR emissions are commonly
observed in the slot region of the radiation belt.
Electric fields in the inner magnetosphere associated with sudden commencements (SCs) areinvestigated using the data measured by the Akebono satellite [Shinbori et al., 2006]. After apassage of a bi-polar waveform associated with fast-mode hydromagnetic waves, the increase of
the convection electric field takes place in the entire magnetic local time sector in the innermagnetosphere. The origin of the convection electric field in the inner magnetosphere is a
plasma motion caused by the compression of the magnetosphere due to the solar wind shock.
Shinbori et al. [2007] investigated electrostatic electron cyclotron harmonic (ESCH) waves inthe low-latitude plasmasphere (MLAT<45◦) by using the long-term plasma wave observation
data obtained from the plasma wave and sounder experiment (PWS) onboard the Akebono
satellite.
Nishimura et al. [2006, 2007a] revealed the generathin mechanism of the so-called"equatorial enhancement of the plasma wave turbulence (EPWAT)”. From the Akebono PWS
measurements theyshowed that the Z-mode waves are excited directly through a wave-particle
interaction rather than the mode conversion from electrostatic waves. The ring-current electrons
originating in the premidnight tail region are accelerated perpendicular to the ambient
magnetic field and confined around the geomagnetic equator because of the conservation of
the first and second adiabatic invariants.
Plasma Wave Instrument (PWI) onboard Geotail spacecraft continues to survey plasma waves
in the terrestrial magnetosphere as well as in the magnetosheath and solar wind regions at the
distance of 10Re to 30Re from the earth for more than 15years since the launch in 1992.
Shin et al. [2005] reported the electrostatic quasi-monochromatic (EQM) waves in thefrequency range near 1 kHz. Geotail spacecraft observations show good correlation of EQM
wave activities with the existence of cold electron beam-like component which correspond to
the electrons accelerated in the bow shock. They show that under the existence of the cold
beam-like component and background electrons with different temperatures, most plausible
wave mode of the EQM waves is electron acoustic wave.
Shiokawa et al. [2005] examined the rapid decrease in Bz just before dipolarizations observedby the GEOTAIL satellite in the near-Earth plasma sheet. The magnetic Bz component
suddenly decreased 2-4 s prior to the dipolarization. Characteristic waves with frequencies of
5-20 Hz and amplitudes of 1-3 mV/m and 5-15 nT/s were observed in the electric and magnetic
field data at the time of the sudden decreases in Bz. They argue that the observed sudden
decreases in Bz prior to the dipolarizations are possibly the explosive growth phase andsubsequent disruption of the tail current caused by the observed characteristic field oscillationsin the lower hybrid frequency range.
Oka et al. [2006] discuss a possible relationship between the Whistler critical Mach
number(M-crit(w)) and the electron acceleration based on Geotail observations. They report thatM-crit(w) seems to regulate the electron acceleration efficiency at the shocks. At the shocktransition layer it is found that the spectral index Gamma of electron energy spectra defined byf(E) proportional to E-Gamma G is distributed between 3.5 and 5.0 in the sub-critical regime,
while the hardest energy spectra with Gamma = 3-3.5 are detected in the super-critical regime.
In the study on the electromagnetic waves radiated in the upstream region of the bow shock,Kasaba et al. [2005] summarized the generation mechanism of electrostatic and electromagnetic
2fp emissions based on the Geotail observations and computer simulations. They also discuss
the electron acceleration in the quasi-perpendicular shock region comparing with intensities of
2fp emissions and shock normal angles.
Kasaba et al. [2005] summarize the characteristics of the DC electric field measurement by
the double probe system, PANT and EFD-P, aboard Geotail. In better conditions, accuracy of Ey
is 0.2 mV/m. The potential accuracy would be better because those values are limited by theaccuracy of the particle measurement especially in low density conditions. In practical use, thecorrections by long-term variation and spacecraft potential are effective to refine the electricfield data.
Hori et al. [2005] studied the electric field by the Geotail spacecraft in the near-Earthmagnetotail during magnetic storms. The observed electric field properties in the near-Earthplasma sheet are basically classified into the two categories: one is characterized by intermittent
bursts of fluctuating duskward electric fields associated with substorm expansions, and the otheris dominated by a relatively steady, weak duskward electric field. The weak strength of theconvection electric field in the latter category is seen even during storm main phase.
Lobe trapped continuum radiation (LTCR) has been observed onboard the Geotail spacecraft,at frequencies as low as 1 kHz in the distant geomagnetic tail region. By comparing the
waveform observations of the LTCR with the 3-d ray-tracing analysis, the possible source
regions of the LTCR is identified as the plasma sheet boundary layer away from the nominal tailaxis and the low latitude boundary layer (Takano et al., 2005).
Morioka et al. [2007] studied detailed features of micro-type-III radio bursts, which areelements of the so-called type III storm, by using long-term observations made by the Geotailand Akebono satellites. Micro-type-III radio bursts are characterized by short-lived, continuous,
and weak emissions. It was found that both micro and ordinary type-III bursts emanated fromthe same active region without interference, indicating the coexistence of independent electron
acceleration processes.
Hashimoto et al.[2005] showed new sources of the Kilometric continuum radiation, which
was first identified with the Geotail Plasma Wave Instrument (PWI) and has been observed withvarious satellites. Using the multiple satellite data, they revealed that the kilometric continuum
can be radiated at the equatorial density irregularities inside the plasmasphere as well as at theplasmapause. Further, IMAGE and Geotail simultaneous kilometric continuum observations
measure a very broad emission cone of up to about +/- 30 degrees.
The auroral kilometric radiation is the intense emissions radiated in the polar region in therelation to auroral activities. Murata et al. [2005] examined the simultaneous observation data of
Geotail and Polar spacecraft. They found the two distinct regions where the AKR is osculated.
One is the night side region at lower region less than 60MLAT and the other is the vicinity ofthe plasma pause regions of the MLAT between 30 and 50 degrees in the day side and between
10 and 30 degrees in the night side.
An empirical formula correlating the Geotail spacecraft potential measured by the single
probe and the electron number density as determined by the plasma wave observations in thesolar wind and broader magnetosphere have been obtained. Using this formula and plasma
particle measurements, the problem how much and how the low-energy plasma exist in themagnetosphere is investigated [Ishisaka et al., 2005].
The extensive collaboration of the Geotail observations and computer simulations was
conducted on the modulated Langmuir waves observed by Geotail. Usui et al. [2005] studied
the amplitude modulation of Langmuir waves using fill particle electromagnetic computer
simulations. They succeeded on explaining it by the nonlinear trapping theory instead of theconventional theories such as the decay instability and the modulational instability.
By using a test-particle simulation, Nakagawa and M. Iizima [2005, 2006] studied velocity
distribution of the solar wind electrons injected into the lunar wake boundary. They showed thatthe pitch angle of the electrons are largely diffused by the electric field at the wake boundary.
The component perpendicular to the backgoround magnetic field became large enough to excite
whistler mode wave as observed by GEOTAIL in the solar wind upstream of the lunar wake.
<Jovian Radio Emission>
Morioka et al. [2004] investigated the characteristics of the Jovian Anomalous Continuum(JAC) in interplanetary space, using Ulysses observation. Some new source characteristics of
JAC were obtained: (1) JAC tends to occur when the solar-wind dynamic pressure decreases
after a rapid increase, (2) JAC appears most likely when the System III longitude of the
sub-solar point is near 270°, and (3) the periodic appearance of JAC is not due to its intensity
modulation but its repeated individual excitation.
Morioka et al. [2006] investigated the occurrence characteristics of Jovian multiple
quasi-periodic bursts based on Galileo spacecraft observations. They showed that Multiple QP
bursts recurrently appeared in a group with a planetary spin period of 10 hr, i.e., they werepreferably excited when Jupiter had a particular spin phase angle with respect to the sun (at asub-solar longitude of System III around 260-320º).

H1.2 Ionospheric Radio Wave<Rocket Experiment>
Ashihara et al. [2005] studied the mid-latitude D-region ionosphere by measuring, onboard
rocket S-310-33, the intensities of radio waves at 238 kHz and 873 kHz transmitted from theground stations. The electron density profile was estimated from absorption of these radio
waves and it is found that there was a thin layer of high electron density of 2.4×103 cm-3 at thealtitude of 89 km. The thickness of its layer is about 0.9～1.0 km.
Ishisaka et al. [2005] studied the ionosphere in the auroral region by the MF radio absorption
method. The SRP-4 rocket was launched at Poker Flat in Alaska on 18 March 2002. The Low
frequency and Medium frequency band radio Receiver (LMR) and the DC Probe System (DPS)
were installed on-board the rocket to estimate the electron density in the D-region as low as 50
km altitude.
The number density of electrons by impedance probe (NEI) instrument provided high-quality
data of the electron density in the midlatitude and auroral ionosphere in the SEEK-2 and DELTA
campaigns, respectively [Wakabayashi et al., 2005a; Wakabayashi et al., 2005b; Wakabayashi
and Ono, 2006]. It measured multi-layered sporadic E layer (Es) and enhancements of theelectron density associated with precipitations of auroral electrons.
The occurrence character of the ionization ledge was investigated by using the topsidesounder experiments on-board Ohzora and ISIS-2 [Uemoto et al., 2006, 2007a]. The ionization
ledge tends to align along the geomagnetic field line, and to appear within local time sectors
from morning (9 LT) to slightly after midnight (2 LT). The occurrence of ionization ledges iscorrelated with eastward electric fields applied in the equatorial ionosphere, which cause
upward plasma drifts.
Simultaneous magnetic conjugate observations of the F3 layer have been performed by using
the meridional ionosonde network located in Southeast Asia (SEALION) between November 16,
2004 and March 31, 2005 [Uemoto et al., 2007b]. A clear dependence of the F3 layer on themagnetic latitude is found. The magnetic latitude dependence can be explained by the plasma
diffusion effects along the magnetic field lines in the magnetic low-latitude region.
For precise measurements of the electron density in the ionosphere, Wakabayashi et al.
[2005a] and Wakabayashi and Ono [2006] developed impedance probes using the direct digitalsynthesizer (DDS) and logarithmic amplifier. It allows measuring the electron density with anaccuracy of less than 3%. The impedance probes were mounted on the S310-31 and S310-32(SEEK-2 campaign, without log amp), and S310-35 (DELTA campaign, with log amp) rockets.
See below for the results.
H1.3 Ground observation and Experiment of Plasma Waves<Solar Radio Bursts>
A new solar radio spectrograph covering frequency ranges from 18 to 38 MHz and 190 to 350
MHz has been installed at the Husafell station in Iceland [Hiyama et al., 2006]. Thirty solar
bursts have been measured since September 2004. They compared our ground measurementwith solar bursts simultaneously detected by the WIND spacecraft.
<ULF Wave>
From the observed frequency (in the ULF range) of the field-line resonance (FLR), one canestimate the plasma mass density along the field line being observed. Kawano et al. [2006]
compared the L profile (at L>2.3) of the electron density during a magnetic storm, observed by
Akebono/PWS, with simultaneous ion density at L=2.07, estimated by Chi et al. [2000] by using
FLR identified in ground magnetometer data. As a result, Kawano et al. suggested that theplasmapause remained outside L=2.07 during the storm but the density within the plasmaspheredecreased.
Takasaki et al. [2006] observed FLR at L~1.4, from which they reported an increase in theequatorial plasma density at L~1.4 during a large storm. This is surprising, because it isusually thought that the plasmasphere shrinks during a storm; Takasaki et al. interpreted theincrease in terms of an outflow of heavy ions (e.g., O+) from the ionosphere to theplasmasphere.
Uozumi et al. [2007] studied the generation and propagation of Pi 2 waves in themagnetosphere by comparing the ground-based signatures of Pi 2, observed by the Circum-pan
Pacific Magnetometer Network (CPMN), with their model calculations. They suggested that thesource region of Pi 2 is located at 9 Re and 22.5 MLT on the equatorial plane. They alsosuggested that, to successfully explain the observations, Pi 2 has to start from the source region
as fast mode waves.
Kawano and Lee [2007] applied, for the first time, the so-called gradient methods tosimulated ground magnetic field data (simulated by an MHD code). They reported that there doexist cases in which the gradient methods successfully identify FLR. They then went further andreported a case in which a non-FLR wave component biases the gradient-method output; thenon-FLR component appears to have arisen from the coupling of an FLR component and acavity-mode component where the two frequencies match.
Tokunaga et al. [2007] applied, for the first time, the Independent Component Analysis (ICA)
method to a Pi 2 event observed by CPMN. As a result, they found that the Pi 2 had two
components; the one component looked, at low latitudes, similar to previously reported cavity
mode, but it had a common waveform even outside the nominal plasmasphere. The othercomponent was localized at nightside high latitudes, suggesting its relevance to substorm
current systems; it is also to be noted that this component was also observed near the dayside
dip equator.
Abe et al. [2006] identified the plume from the ground for the first time by using ULF waves
measured by ground magnetometers. They confirmed the identification by comparisons with thedata from the EUV imager on board the IMAGE satellite.
Iyemori et al. [2005] reported a long-period Pc5 pulsation in Thailand shortly after the onset
time of the Sumatra earthquake on December 26, 2004. They suggested that the Pc5 was
generated by dynamo action in the lower ionosphere, set up by an atmospheric pressure pulse
which propagated vertically as an acoustic wave when the ocean floor suddenly moved
vertically. This study was followed by the study of Shinagawa et al. [2007], who used atime-dependent two-dimensional nonhydrostatic compressible atmosphere-ionosphere model,
ran numerical simulations, and successfully reproduced the atmospheric pressure pulse.
Tsurutani et al. [2006] reviewed geomagnetic activity due to corotating solar wind streams.
They demonstrated that geomagnetic storms associated with high-speed streams/CIRs(corotating interaction regions) have the same initial, main, and “recovery” phases as those
associated with ICME (interplanetary coronal mass ejections)-related magnetic storms but thatthe interplanetary causes are considerably different. They showed that elongated storm“recovery” phases are caused by nonlinear Alfven waves within the high streams proper, and theacceleration of relativistic electrons occurs during these magnetic storm “recovery” phases.
Sakaguchi et al. [2007] reported very good correspondence between 13 isolated auroral arc
events at subauroral latitudes and Pc 1 geomagnetic pulsations using one-year data from
Athabasca, Canada (magnetic latitude: 62 deg, L=4.6). The observed Pc 1 frequencies were
almost the same as the frequencies of He+ electromagnetic ion cyclotron (EMIC) waves at theequatorial plane connected to observed isolated arcs. These results indicate that interactions ofspatially-localized EMIC waves with ring current ions cause high-energy ion precipitation andassociated isolated auroras at subauroral latitudes.
<Polar Region Experiment>Miyake et al. [2004] carried out successfully the PPB experiment in Antarctica in January
2003, and recently reported the observational results such as the Pc1 pulsations, ELF hiss, polarchorus and auroral hiss. In the PPB experiment, two challenging techniques for the datatransmission were carried out. First, all the observed data were transmitted directly from theballoons to National Institute of Polar Research in Japan, by way of the IRIDIUM satellites forthe world-wide mobile telephone.
Ozaki et al. [2007] observed natural ELF/VLF waves (chorus and hiss) in Antarctica from
December 2005 to December 2006 at three sites near Showa Station, which measured intensities
and polarizations of ELF/VLF magnetic fields. With the preliminary analysis they haveconfirmed that the intensities and polarizations of the observed waves could be used to calculate
their ionospheric exit points, during substorms as well as in quiet times. Such information will
provide a quantitative clue to the stereoscopic structures of the ELF/VLF propagation in thepolar ionosphere and magnetosphere.
Optical observations of flickering aurora by a high-speed imaging photometer system werecarried out at Syowa Station in 1998 [Sakanoi et al., 2005]. They made a comparison study
between observed parameters of flickering aurora and theoretical values of dispersive Alfven
waves and demonstrated that observed flickering aurora would be produced by electron flux
modulations by electromagnetic ion cyclotron waves or inertial Alfven waves in the auroral
acceleration region located over the altitude range of about 2000–5000 km.
<Sub-Ionopsheric Radio Waves including Seismic and lightning Emissions>
Ionospheric Alfven Resonances (IARs) as a kind of resonance phenomenon in the ionosphereand mangetosphere, were observed in Kamchaktka, Russia (L = 2.1) by Hayakawa et al. [2004],
who have reported its statistical results on the spectral resonance structures in the ULF /ELF
range from 0.1 to 5.0 Hz on the basis of the long-term observation during 2.5 years. Then,
Surkov et al. [2006] have presented a theory for mid-latitude IARs excitation due toelectromagnetic waves radiated from the lightning discharges, and have found that nearby
thunderstorms in a range of 1000 - 2000 km make a main contribution to IARs.
ELF wave phenomena in the Earth-ionosphere cavity, known as Schumann resonance, havebeen studied in order to monitor the lower ionosphere and global lightning activity. Ando et al.
[2005] have developed an algorithm to deduce the global lightning activity map as an inverse
problem to the ELF data observed at a few stations in the world. Anomalous Schumann
resonance effects have been found for earthquakes by Hayakawa et al. [2005], who have found
an anomaly in Schumann resonance (e.g., enhancement in the fourth harmonic etc.) in Japan, in
possible association with a large earthquakes in Taiwan. They have interpreted that this anomaly
is due to the interference between the direct signal from a major lightning source in America andthe signal scattered from the Seismo-ionospheric perturbation over Taiwan.
Nickolaenko and Hayakawa [2007] have reviewed the latest works on Schumann resonancesand related ELF transient events during the last several years, including ionospheric
non-uniformities, the use as a global thermometer, new objects for studies, and new results in
old problems.
Nickolaenko et al. [2004] have developed a computer algorithm for accelerating theconvergence of the time series computations of the ELF pulsed waveforms propagated in the
Earth-ionosphere waveguide.
Hayakawa [2007] has reviewed the subionospheric VLF/LF propagation during earthquakes,
and have presented event and statistical studies on the correlation of ionospheric perturbations
as seen by VLF/LF and earthquakes with large magnitudes, say with magnitude larger than 6.0.
Also, a few possible mechanisms have been suggested and discussed.
By using the full-wave method, Ozaki et al. [2004] have calculated the ionospheric
penetration of the ELF/VLF electromagnetic field radiated from a dipole source on the ground.
The results have shown a clear difference in day and night wave propagation characteristics.

They have examined the possibility of detecting the electromagnetic wave radiated by anearthquake, directly onboard a satellite.
Higashi et al. [2005] studied the anomalous electromagnetic signals onboard satellite in theionosphere and the lower magnetosphere over seismic areas. In order to estimate the wave
intensities related with seismic activity, they performed a numerical analysis of theelectromagnetic waves in the lower ionosphere radiated from an underground transient dipole
source.
Tsutsui [2005] detected an EM pulse just when an earthquake occurred on January 6 in 2004,
and found that the arrival direction of the pulse pointed toward the earthquake epicenter. And
by examining dispersion characteristic curve seen in frequency dynamic spectra (f-t diagram) of
the detected EM pulse, the propagation distance was determined.Recently, he developed new
analysis method to determine arrival directions of the EM pulses. [Tsutsui et al. 2007].
Seismogenic ULF emissions were detected prior to some large earthquakes ; for example,
2004 Niigata-Chuetsu earthquake [Ohta et al., 2005; Hayakawa et al., 2006] and 2004 Indonesia
Sumatra earthquake [Ohta et al., 2007]. Ohta et al. [2005] performed the direction finding from
Nakatsugawa, Japan and found that the observed azimuthal directions are consistent with theepicentral directions of both earthquakes, giving a strong evidence on the precursory ULF
emissions.
Some sophisticated signal processings were developed and utilized to detect any weakseismogenic ULF emissions [Serita et al., 2005; Hattori et al., 2006; Ida et al., 2006; Ida andHayakawa, 2006]. Ida et al. [2006] and Ida and Hayakawa [2006] have applied the fractal(mono- and multi-) analyses to ground-based ULF data to suggest that those fractal analysis arevery useful in examining the nonlinear process (self-organized criticality) taking place in thelithosphere.
Hayakawa et al. [2007] have reviewed seismogenic ULF emissions, starting from earlier tothe latest results. The most important conclusion from all ULF events reported before, is that
there must be a threshold of the possible detection of seismogenic ULF emissions as functionsof earthquake magnitude and epicentral distantce. Also, the generation mechanisms of ULF
emissions (microfracturing, electro-kinetic effects etc.) are also discussed.
Nagano et al. [2006] and Yagitani et al. [2006] have developed a lightning detection system
to determine the lightning locations by observing the sferic waveforms at a single station.
Compared with the lightning locations identified by a conventional lightning location system(LLS) with multiple stations, it has been confirmed that the developed system could locate thelightnings within the distance of several hundred km with the location errors of about 10%, for
the VLF sferics measured with distinguishable pulse trains.
H2. Theory and Computer Experiment on Plasma Waves
H2.1 Wave Propagation and Wave-Particle Interaction
In order to explain the solar wind transport across the low latitude magnetopause, Matsumotoand Hoshino [2004, 2006] and Matsumoto and Seki [2007] proposed new turbulent transportmechanisms by the secondary instabilities excited by the primal Kelvin-Helmholtz instability(KHI). It was found by 2-D MHD and full particle simulations that the secondary
Rayleigh-Taylor instability greatly contributed to the formation of a broad mixing layer by
exciting large amplitude electrostatic fields. 3-D MHD simulations also found a new secondary
Magneto-Rotational instability excited inside a vortex. This type of 3-D secondary instability
not only enhances a mixing process (in the magnetosphere) but also transports the kinetic
energy in the direction of the ambient magnetic field (ionosphere).
Nonlinear evolution of the electron two-stream instability is systematically studied by a seriesof two-dimensional particle-in-cell simulations [Umeda et al., 2006a]. Detailed stability

conditions of electron phase-space holes and electrostatic wave emission mechanism fromphase-space holes are revealed.
A numerical method for solving linear dispersion equation for Maxwellian ring velocity
distribution function is developed [Umeda, 2007a]. Generation and competition processes andelectrostatic electron cyclotron harmonic (ECH) waves and electromagnetic whistler mode
waves are examined by a two-dimensional particle-in-cell simulation [Umeda et al., 2007].
A robust numerical interpolation scheme for Vlasov code simulations is developed by Umeda
et al. [2006]. The code is applied for generation mechanism of Langmuir wave packets in spaceplasmas. It is shown that Langmuir waves are spatially modulated by highly nonlinear processes
involving both coherent trapping and incoherent turbulent mechanisms [Umeda, 2006, 2007b].
A parametric decay process of Alfven waves into ion acoustic waves is examined by ahigh-resolution magneto-hydro-dynamic (MHD) simulation [Tanaka et al., 2007]. It is shownthat sinusoidal Alfven waves propagating in a radially expanding plasma exceed an amplitude
threshold of the decay instability, exiting forward density fluctuations and backward-scattered
Alfven waves. The density fluctuations also generate shocks and discontinuities, which maylead to turbulence of Alfven waves. Diffusion of energetic particles in such turbulence is studied
by a test particle simulation by Otsuka et al. [2007].
A new model to excite collsionless shocks in computer simulations is developed by Umeda
and Yamazaki [2006]. The new model allows us to follow full-kinetic dynamics of collisionlessshocks in the shock rest frame, which is useful to perform a long-time simulation run.
Resonant diffusion processes of high energy electrons are studied numerically by using an
original simulation scheme with hot electrons including fully relativistic effects and a fluid ofcold electrons [Katoh et al., 2005]. A difference between results from their simulation and thequasi-linear diffusion is identified, indicating the importance of the nonlinearity which is notincluded in the quasi-linear theory.
A mode conversion process from slow X-mode waves to fast X-mode waves by the tunneling
effect has been studied by solving Maxwell equations numerically [Katoh and Iizima, 2006].
The mode conversion is effective where the width of the evanescent layer between the local
UHR frequency and the local fast X-mode cut-off frequency, is of the order of the wavelength of
the incident slow X-mode waves. The result indicates the importance of the mode conversion in
the auroral zone and magnetopause.
The electric field structure around the moon is studied by using a 2-dimensional,
electromagnetic full particle simulation [Kimura and Nakagawa, 2006]. A plasma wake isformed behind the moon in the solar wind flow, and more intense electric field is produced at
the terminator region of the moon due to the absorption of the plasma particles at the surface ofthe moon.
Katoh and Iizima [2006] studied the mode conversion process from slow X-mode waves tofast X-mode waves by the tunneling effect by means of the computer simulation. On the basis of
the new approach by the simulation, they have confirmed that the mode conversion to the fast
X-mode waves is especially effective in a case where the width of the evanescent layer which
exists between the local UHR frequency and the local fast X-mode cut off frequency is of theorder of the wave length of the incident slow X-mode waves.
Triggering process of VLF triggered emissions is studied by a self-consistent electron hybrid
simulation with a homogeneous [Katoh and Omura, 2006a] and a dipole magnetic field model[Katoh and Omura, 2006b].
Katoh and Omura [2006a] studied frequency variation of a coherent whistler-mode wave in a
homogeneous magnetic field. Simulation results show that an injected whistler-mode wave
packet grows due to an instability driven by temperature anisotropy and the amplified wave
packet triggers emissions with frequency shift during its propagation. They clarified that theresonant currents due to the nonlinear wave-particle interaction play significant roles in both
wave growth and frequency variation. Based on the simulation results, we show that the range

of the frequency shift in a homogeneous system is quantitatively estimated by the trapping
frequency of trapped electrons.
Katoh and Omura [2006b] studied the generation mechanism of VLF triggered emissions in a
dipole magnetic field. The evolution of a wave packet propagating along a reference magnetic
field line is solved by Maxwell's equations, while the bounce motion of energetic electrons in
the nonuniform magnetic field is taken into account. They found that a triggered emission with arising tone is generated near the equatorial region after the wave packet passes through themagnetic equator, and 26% rising from the original frequency of the injected wave packet isreproduced.
The simulation model with a dipole magnetic field used in Katoh and Omura [2006b] hasbeen applied to the study of the generation mechanism of whistler-mode chorus emissions[Katoh and Omura, 2007a]. Katoh and Omura [2007a] reproduced chorus emissions withrising tones by the electron hybrid simulation. They assumed energetic electrons forming ahighly anisotropic velocity distribution in the equatorial region. In the early stage of thesimulation, coherent whistler-mode waves were generated from the equator through an
instability driven by the temperature anisotropy of the energetic electrons. During the
propagation of the whistler-mode waves, they found formation of a narrowband emission withnegative frequency gradient (NEWNFG) in the spatial distribution of the frequency spectrum inthe simulation system.
Dynamics of energetic resonant electrons interacting with whistler-mode waves has beenstudied by a test-particle simulation with a dipole magnetic field and a coherent whistler mode
wave [Omura and Summers, 2006]. A very efficient acceleration mechanism called relativistic
turning acceleration (RTA) has been found in the test particle simulation, and it is analyzed
theoretically [Omura et al., 2007], The RTA process has also been found in the self-consistent
simulation of chorus wave generation [Katoh and Omura, 2007b].
Sugiyama and Kusano [2007] developed a new simulation model to interlock the fluid
simulation and kinetic simulation with particle-in-cell model, and confirmed smoothpropagation of Alfven wave through boundaries of small-scale and MHD domain.
Parametric instabilities of incoherent Alfven waves are intensively studied by Nariyuki and
Hada [2005, 2006a, 2006b, 2007a,2007b,2007c].
Katoh et al. [2006] studied generation of ion cyclotron waves through the ion pickup processsurrounding Io by hybrid simulation. They simulated the excitation of ion cyclotron waves anddiscuss the modification of the velocity distribution of picked-up ions due to the wave-particle
interaction.
2.2 Antenna in space plasma
The characteristics of dipole antenna or probe antenna have been studied in two ways; one is theconstruction of electrical equivalent circuit using the AKEBONO and GEOTAIL observation
data. Another approach is the computer simulation using the particle code. Usui et al. [2006]
have been studying the antenna properties of a dipole antenna immersed in magnetized plasma
by performing PIC (Particle-In-Cell) electromagnetic simulations.
Higashi et al. [2005] studied the effective length and the impedance of the wire dipole
antennas onboard the Akebono satellite. The effective length of each wire dipole antenna isestimated to be nearly the half of its tip-to-tip length of 60 m, which is consistent with theconventional assumption of the effective lengths of the dipole. On the other hand, the estimatedcapacitance and resistance exhibit specific spin variation, which would be caused by the plasma
sheath formation around the antenna wires, depending on the angle between the antenna
direction and the geomagnetic field line.
Imachi et al. [2006] have investigated the low-frequency characteristics of wire antennas
onboard spacecraft like Geotail. With the ground-based “Rheometry Experiment” using anantenna scale model to pick up an electric field generated inside a water tank, they have foundthat for a wire dipole antenna covered with a thin insulator except for its tips, the antenna’s
effective length is almost equal to its tip-to-tip length at very low frequencies (less thanhundreds of Hz), while it becomes half of it at higher frequencies.
The frequency dependence of the effective length has been explained by theoretical
calculations as well as by numerical electromagnetic simulations [Imachi et al., 2007].
Especially the simulations have revealed the detailed spatial structures of ambient electric fields
and potentials deformed under the influence of the antenna wires. The structure of deformed
electric fields and potentials varies with frequency, which can quantitatively explain thefrequency dependence of the antenna’s effective length.
H3. New Projects for Lunar and Planeatary Plasma Wave Study< KAGUYA >KAGUYA was launched at 10:31:01 a.m. on September 14, 2007 (JST) from Tanegashima
Space Center by JAXA. KAGUYA consists of a main orbiting satellite at about 100km altitude
and two small satellites (Relay Satellite and VRAD Satellite) in polar orbit. The orbiters will
carry instruments for scientific investigation of the Moon, on the Moon, and from the Moon.
The Lunar Radar Sounder (LRS) on-board KAGUYA has been planned to provide the data ofsubsurface stratification and tectonic features in the shallow part (several km depths) of thelunar crust, by using an FM/CW radar technique in HF (~5MHz) frequency range. The LRS
consists of three subsystems: the sounder observation (SDR), the natural plasma wave receiver(NPW), and the waveform capture (WFC). Knowledge of the subsurface structure is crucial tobetter understanding not only of the geologic history of the moon, but also of the regional andglobal thermal history of the Moon, and also of the origin of the Earth-Moon system. In
addition to the subsurface radar experiment, LRS will provide the spectrum of plasma waves,and solar and planetary radio waves in wide frequency range covering from 10 Hz to 30 MHz.
In order to achieve the lunar subsurface sounding and planetary radio wave observations by
the LRS, strict electromagnetic compatibility (EMC) requirements were applied for all
instruments and whole system of the spacecraft. The EMC performance of the spacecraft was
finally evaluated in the system EMC test. In the EMC test, following new techniques wereintroduced: (1) Systematic control and evaluation of common-mode current noises were first
performed to improve the spacecraft EMC performance. (2) Onboard battery operation was
utilized for reduction of ambient broadband noises during EMC measurements.
The WFC, which is a subsystem of the LRS onboard KAGUYA, is a high-performance andmulti-functional receiver for the measurement of plasma waves and radio emissions. Specificwave phenomena of interest to be obtained from the WFC data are dynamics of lunar wake as aresult of solar wind-moon interaction, physics of mini-magnetosphere caused by the magnetic
anomaly of the moon, kilometric radiation originated from the Earth, solar radio emissions, andmany kinds of plasma waves in the Earth’s magnetosphere.
Kobayashi and Ono [2006, 2007] propose a technique to estimate a detectability ofsubsurface echoes and a roughness parameter of a planetary surface by means of a sounderexperiment. The technique was examined by simulations of planetary sounding observations
which is based on physical optics, and demonstrated to estimate the RMS gradient of theplanetary surface in the range from some fraction of degrees to about ten degrees. The technique
can be applied to the radio sounder observation of Mars as well as that of the Moon by
KAGUYA/LRS.
<BepiColombo>
The BepiColombo is the science mission to Mercury. It is the first collaborative space
program of JAXA and ESA. The BepiColombo mission consists of two individual spacecraftcalled MPO (Mercury Planetary Orbiter) and MMO (Mercury Magnetospheric Orbiter). Twospacecraft of the BepiColombo will be launched in 2013.
Plasma Wave Investigation (PWI) was proposed in collaboration of the Japanese andEuropean science teams. The targets of the PWI are plasma/radio waves in and around the
Mercury magnetosphere. The MMO Payload Review Committee in JAXA selected the PWI for
the science payload onboard MMO spacecraft in 2005.
The PWI investigates plasma/radio waves and DC electric field in Mercury magnetosphere.
The detailed science objectives of the PWI are described by Matsumoto et al. [2006]. The PWI
consists of two components of receivers (EWO: Electric Field Detector/Wave-Form
Capture/Onboard Frequency Analyzer, and SORBET: Spectroscopie Ondes Radio & BruitElectrostatique Thermique), two sets of electric field sensors (WPT: Wire-Probe antenna, andMEFISTO: Mercury Electric Field In-Situ Tool), two kinds of magnetic field sensors (LF-SC:Low Frequency Search Coil, and DB-SC: Dual-Band Search Coil), and the antenna impedance
measurement system (AM2P: Active Measurement of Mercury’s Plasma).
After the Preliminary Requirements Review by JAXA in 2005, the PWI team started todesign the receiver system and sensors. The specifications and designs of the PWI are describedby Matsumoto et al. [2006] (whole PWI system), Blomberg et al.[2006a, 2006b](MEFISTO),
Moncuquet et al. [2006](SORBET), and Trotignon et al.[2006](AM2P).
<ERG Mission>
The Earth’s inner magnetosphere (inside 10 Re) is a region where particle energy increases tothe relativistic energy range. This region is very important as a laboratory where high-energy
particle acceleration can be directly measured in a dipolar field configuration, as well as forhuman activities in space. Shiokawa et al. [2006] reviewed unsolved scientific problems of theinner magnetosphere and proposed a new project name ERG that will provide new insights into
the dynamics of the inner magnetosphere. They made a rough assessment of possible
instruments and options for various scientific objectives for the ERG project.
<Jupiter Mission>
The Solar-Sail Project has been investigated by JAXA as an engineering mission with a small
orbiter into the Jovian orbit [Kasaba et al., 2007]. This paper summarizes the basic design ofthis project and possible Jovian system studies by this opportunity. The small Jovian orbiter
acompanied with the Solar-Sail Project will try to establish the technical feasibility of such
future outer planet missions in Japan. The main objective is the second target, the Jovian
magnetospheric and auroral studies with its limited payload resources. Radio and plasma wave
instruments are considered as one of base instruments.
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Acknowledgments
The editors thank Prof. M. Hayakawa, Drs. H. Kojima, H. Usui, T. Nakagawa, Y. Kasahara, S.
Yagitani, H. Kawano, and Y. Miyoshi for their collaboration in editing the report.