Based
on the papers published from November of 2001 to October of 2004, we have
compiled major achievements in the field of plasma waves and related studies
made by Japanese scientists and their collaborators. We have categorized the
studies into two groups. One is based on observations and experiments, and the
other is theories and computer simulations. Studies in each category are
further divided into several sections. Each section provides a specific summary
of important scientific achievements rather than a comprehensive 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 we have collected from the Japanese Commission H members.
The three years covered by this report mark the start and growth
of the ground-based remote-sensing of the magnetospheric
plasma mass density by using ULF waves; from a geomagnetic field-line eigen-frequency, that is identified by applying method(s)
in a group of methods called "gradient methods" to the data from two
ground magnetometers separated in latitude by about 1 degree, one can estimate
the plasma mass density at the equatorial point along the field line that runs
through the midpoint of the two magnetometer sites. By applying this procedure
to a chain of ground magnetometers, one can
remote-sense the L-dependence of the magnetospheric
equatorial plasma mass density.
There exist papers on Pc pulsations: Matsuoka et al. [2002]
studied high-latitude narrow-band Pc3 pulsations by using ground magnetometer
arrays, SuperDARN radars, and the GEOTAIL
satellite. As a result they found
that, at times, there existed high coherence between the pulsations in the dawn
magnetosheath and on the ground, from which fact they
suggested that the driving source was located in the magnetosheath.
Tanaka et al. [2004] statistically examined the longitudinal structures of
coherence, amplitude, and phase of the Pc-3 H component by using three
longitudinally separated sub-equatorial stations, and reported for the first
time a nearly in-phase structure in the 0730-1700 LT sector and a nearly
180-deg phase jump across 0730 LT. Motoba et al. [2002; 2003; 2004] reported the existence of,
and studied, Pc5-range magnetic-field oscillations on the ground that were
actually caused by oscillations of a DP2-type current system.
Electric and magnetic field variations inside the plasmasphere associated with sudden commencements (SCs) are analyzed based on the Akebono satellite
observations. Shinbori et al. [2004] showed that
intense electric field disturbances with a bi-polar waveform associated with SCs are followed by a dumping oscillation with a period of
Pc3-4 ranges. The dumping oscillation persisted for about 3-7 minutes in the
equatorial region of the plasmasphere. The phase
relation of Ex and Bz components of the oscillation
reveals that there is a phase lag of about 90 degrees with compression nature.
From this result, they concluded that the dumping oscillation generated by SC
disturbances may be fast mode waves propagating in the plasmasphere.
The Hall-induced inductive shielding effect (ISE) of the
ionosphere affects currents and electric fields that have impinged into the
ionosphere from the magnetosphere.
Yoshikawa et al. [2002] developed a new formula describing the inductive
behavior of the magnetosphere- ionosphere-atmosphere-Earth system, and by using
it, they investigated the ISE on geomagnetic pulsations. As a result, they found that dayside Pc
3-4 pulsations may be frequently affected by the ISE.
Many scientists worked on Pi2 pulsations: Yamaguchi et al.
[2002] presented a case study in which a bursty bulk
flow (BBF) in the plasma sheet started prior to the corresponding ground Pi2
onset, but was preceded by the corresponding Pi2 onset at GOES8. From this and another feature they
suggested that the BBF was not the cause of the low-latitude Pi2. Shiokawa et al. [2002] examined 10s-resolution
ground-observed auroral images at the times of Pi2s,
but did not find an oscillation of the auroral
luminosity synchronized with the oscillation of Pi2. Higuchi et al. [2002] presented a new
method to identify the Pi2 onset time; the method is based on statistical
science and uses, e.g., Akaike Information Criterion
(AIC). Saka et al. [2002; 2004] suggested, mainly
based on observations at the synchronous orbit, that impulsive dusk-to-dawn
current near the nightside synchronous orbit, which
current is closed by field-aligned currents, is a source of Pi2.
Nose et al. [2003] investigated a morning-side Pi2 using
ground stations and the ETS-VI and EXOS-D satellites; from the dependence on
(L,LT) of the observed waveform, period and phase, they concluded that the Pi2
was caused by the plasmaspheric cavity mode resonance
and that its longitudinal structure was rather uniform. Uozumi et al.
[2004] investigated propagations of high-latitude Pi2s observed by CPMN ground
stations. With the aid of POLAR/UVI
auroral images, they found that Pi2 was observed
earlier (by about35s) in the polar cap than in the auroral
region; thus, Pi2 in the polar cap is to be used to determine the substorm onset time.
They also found the starting MLT of Pi2 to be 22.5 hr.
Fujita et al. [2001] numerically calculated how a Pi2
pulsation propagates in the magnetosphere- ionosphere system. They also showed
its relation with the substorm current wedge [Fujita
et al., 2002]. In recent years, a cavity resonance mode has been widely
believed as the main mechanism of low-latitude Pi2 pulsations. Although it has
been implicitly assumed that the frequency should be the same throughout
different local time zones for cavity resonance mode, Kosaka
et al. [2002] and Han et al. [2003] found a local time dependence of the
dominant frequency. To explain
their results, Fujita and Itonaga [2003] made a
numerical simulation and showed that the frequency can be local time dependent
in the longitudinally non-uniform plasmasphere. The propagation
mechanism of Pi2 pulsations has also been investigated using satellite data by
and Han et al. [2004]: They confirmed that the cavity resonance mode is the
most plausible mechanism in low latitudes.
As regards Sudden
Commencements/Impulses (SC/SI), Takeuchi et al. [2002a]
reported that negative SIs are not caused by reverse
shocks but by varied structures such as tangential discontinuities at high-low
speed stream interfaces, front boundaries of interplanetary magnetic clouds,
and trailing edges of heliospheric plasma
sheets. Takeuchi et al. [2002b]
reported that, for an SC with long rise time (30 min), the corresponding
interplanetary shock, observed in the solar wind, was as sharp as usual SCs, but its normal was highly inclined duskward. Araki et al. [2004] statistically
analyzed SCs, and reported that the rise time is
essentially determined by time for an interplanetary shock to sweep geoeffective magnetopause length L, which they estimated to
be about 30 Re.
Nakagawa et al. [2003] reported left-handed ULF waves with
frequency of 0.3-1.1 Hz detected by GEOTAIL at 27 lunar radii upstream of the
moon when GEOTAIL was located on field lines that ran through the lunar
wake. They explained the observation
by polarization-reversal of right-handed, sunward-propagating electron whistler
waves with frequencies above 1.4 Hz in the solar wind rest frame, and suggested
that the waves were excited by electron beams that had field-aligned-flowed
anti-sunward through the lunar wake.
The GEOTAIL spacecraft has observed Lobe Trapped Continuum
Radiation (LTCR) in the Earth's distant magnetotail
in the frequency range from several hundreds of Hz up to 8 kHz. Takano et al.
[2001, 2004] have estimated the generation region of the LTCR by means of
direction finding and three-dimensional ray tracing analyses. The direction
finding analysis with the wave form data of the LTCR has shown that most of the
LTCR propagates along the dawn-dusk direction. Comparing this result with the
three-dimensional ray tracing analysis, the generation region of the LTCR has
been estimated to be located around the plasma sheet boundary layer and the low
latitude boundary layer of the distant magnetotail.
The low latitude boundary layer (LLBL) is a region where
solar wind momentum and energy is transferred to the magnetosphere. Enhanced
“broadband” electric plasma waves from <5 Hz to 105 Hz and magnetic waves
from <5 Hz to the electron cyclotron frequency are characteristic of the LLBL.
Tsurutani et al. [2003] reviewed wave-particle
interactions, with focus on cross-diffusion rates and the contributions of such
interactions toward the formation of the boundary layer and presented a
scenario where the global solar wind-magnetosphere interaction is responsible
for the auroral zone particle beams, the generation
of plasma waves, and the formation of the boundary layer.
Shinbori et al. [2002]
reported that plasma wave phenomena associated with sudden commencements (SCs) are analyzed by using the Akebono satellite
observation data which have been carried out for more than 13 years since March
1989. The 719 cases of SC events showed an enhancement of plasma waves with
one-to-one correspondence to the SC onsets measured at Kakioka
in the inner magnetosphere, plasmasphere, and polar
ionosphere. In the middle latitude and in the equatorial region of plasmasphere, electromagnetic whistler, LHR, and ion
cyclotron mode waves are generated, while in the high latitude region, clear
enhancements of electrostatic whistler mode waves with broad-banded spectra are
observed.
From time difference between the onset times of SC on the
ground and the plasma wave enhancements, Shinbori et
al. [2003b] verified that the propagation nature of the SC disturbances deduced
from these observations has shown two folding signatures; one route is crossing
the equator regions with an average speed of 389.5 km/s, and the other route is
passing the polar regions entering from the cusp region and propagating from
the dayside to the nightside polar ionosphere with an
average speed of 47 km/s.
Higashi et al. [2004] estimated the impedance of the wire
dipole antennas onboard the Akebono satellite by using the electromagnetic
field observations for Omega navigational signals. The estimated capacitance 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. [2004]
studied the effective lengths of a wire dipole antenna onboard spacecraft and
found the frequency dependence from DC (static) to AC (wave) electric fields by
a “rheometry” experiment, where a scale model of the
antenna is immersed in a water tank with two electrodes creating a quasi-static
electric field in it.
The SS-520-2 rocket experiment was carried out over Ny-alesund,
Two large scientific balloons (PPB: Polar Patrol Balloon)
were launched on
Singh and Hayakawa [2001, 2003] examined the relative merits
of ducted and non-ducted propagations of low-latitude whistlers critically in
the light of works done mostly in the Asian countries. They found a growing
consensus in favor of the non-ducted pro-longitudinal mode of propagation for
nighttime whistlers, and ducted propagation for daytime whistlers. Hayakawa and
Ohta, [2003] reviewed the direction finding systems
and suggested the importance of the use of direction finding in VLF studies
with a few experimental examples.
In an attempt to monitor subsurface VLF electric field
changes associated with earthquakes, a borehole antenna has been installed at
Hayakawa and Nickolaenko [2001]
reviewed lightning effects onto the mesosphere and lower ionosphere extensively
in relation to the generation of sprites and elves and the associated ELF
transients. Hobara et al., [2001, 2003] and Hayakawa
et al, [2004b] have carried out the observation of sprites for the winter
lightning in the Hokuriku area of Japan and found that sprites are really
triggered mainly by +CGs whose charge moment change
is exceeding the threshold of 200 ~ 300 C·km.
Otsuyama et al. [2002,
2003a, 2004a, 2004b] studied the VLF signature of ionospheric
perturbations (Trimpis) associated with winter lightnings in the Hokuriku area. They found that there is
no significant difference in the Trimpi occurrence
rate between – and + CGs. Otsuyama
et al. [2002] also performed an FDTD computer simulation for VLF scattering in
the Earth-ionosphere waveguide. Molchanov et al. [2001] investigated the modulation in the
amplitude and/or phase of subionospheric VLF
propagation. The result indicated the significant power in the frequency range
of atmospheric gravity waves.
Hayakawa et al. [2004a] have presented the long-term
observational results on the ionospheric Alfven resonance at middle latitudes on the basis of
observation at
Ando et al. [2002] have theoretically investigated the
penetrations of power line harmonics and compared with the previous satellite
VLF observation. Soloviev and Hayakawa [2002, 2004] have proposed an
algorithm to study the VLF scattering with taken into account a 3D local ionospheric irregularity over the ground of the solar
terminator transition on the basis of a mathematical model, an asymptotic
theory and an appropriate numerical method.
Hayakawa and Otsuyama [2002], Otsuyama et al. [2003b] and Otsuyama
and Hayakawa[2004] have applied the FDTD method to the global Schumann
resonances. They demonstrated that this application is expected to be very
useful for the complicated ionospheric models
(day/night asymmetry, local ionospheric perturbation
etc.). Ando and Hayakawa [2004] have studied the inverse problem extensively
for the Schumann resonance data observed at a few stations in the world and
deduced the global distribution of background lightning activity. Nickolaenko et
al., [2004a, 2004b] have developed an algorithm to accelerate the convergence
of the time domain formal solution for the natural ELF transient pulses in the
Earth-ionosphere waveguide.
Electrostatic waves associated with reconnection phenomena
in the dayside magnetosphere region, were reported by Matsumoto et al. [2003]
using the observation results by GEOTAIL skimmed along the dayside
magnetopause. They confirmed the 3-dimensional multiple x-line magnetic reconnections
take place in the same time period. The observed electrostatic waves are
Electrostatic Solitary Waves (ESW) and Amplitude Modulated Electrostatic Waves
(AMEW). They showed that the
enhanced broadband electrostatic emissions associated with reconnection are not
random noises but are nonlinear coherent structures which may provide important
dissipation in the electron diffusion region during reconnection.
In the auroral zone and polar
cap region outside the plasmapause, Shinbori et al. [2002, 2003b] reported that electrostatic
whistler mode waves with broad-banded spectra suddenly appear below the local
electron cyclotron frequency associated with SC onsets measured at Kakioka in the plasma wave data of the Akebono satellite.
The ratio (E/H) of electric and magnetic field intensity of the plasma waves at
17.8 kHz obtained by the VLF instruments onboard the Akebono satellite is much
larger than that of electromagnetic waves in vacuum. This result suggested
electrostatic nature of the whistler mode waves. From simultaneous observation
of low energy electrons by the Akebono satellite, Shinbori
et al. [2003b] showed that the electrostatic whistler mode waves are excited by
electron beams with an energy range of less than 100 eV.
Shin et al. [2004] showed the waveforms of the intense
electrostatic waves observed in the downstream region are quasi-monochromatic.
They named their waves Electrostatic Quasi-Monochromatic (EQM) waves. By
comparing the plasma wave data with electron data, they found the good correlation
of the observations of EQM waves with beam-like cold electrons. They suggested
that the EQM waves are electron acoustic mode waves based on the preliminary
linear dispersion analyses.
Using the Plasma Wave Instrument (PWI) data from the
GEOTAIL satellite, Nagano et al. [2003a] showed that the angular intensity
distribution of the Continuum Radiation (CR) received in the magnetotail regions changes from isotropic to anisotropic
above a specific frequency. They interpret the transition as evidence of the magnetosheath cavity trapping of terrestrial radiation and
that the magnetosheath plasma relaxes at the local Alfven speed, rather than the solar wind convection speed.
Kilometric continuum (KC) radiation was first identified
from GEOTAIL plasma wave observations. This emission has a frequency range that
overlaps that of the auroral kilometric radiation
(AKR) but is characterized by a fine structure of narrow bandwidth with nearly
constant or drifting frequency. Its source region is probably associated with
the low-latitude inner magnetosphere. Menietti et al.
[2003] reported new high-resolution electric and magnetic field observations of
KC obtained by the Polar plasma wave instrument in the near-source region.
These observations show intense electrostatic and less intense electromagnetic
emissions near the magnetic equator at the plasmapause.
Simultaneously, GEOTAIL, located at 20 to 30 RE in radial distance, observes KC
in the same frequency range. These data support a possible mode-conversion
source mechanism near a region of high-density gradient.
Green et
al. [2004] compared a year's worth of observations of kilometric continuum (KC)
from the plasma wave instrument (PWI) on GEOTAIL and extreme ultraviolet (EUV)
images of the plasmasphere from IMAGE. KC was observed to be associated with
density depletions or notch structures in the plasmasphere. IMAGE observations from the radio plasma
imager (RPI) during passage through a plasmaspheric
notch structure found that KC was generated in or very near the magnetic
equator at steep gradients in density.
GEOTAIL and POLAR Plasma Wave (PWI) and WIND Radio
Science (WAVES) experiments’ detections from typically widely separated
positions of emissions are compared and contrasted by Anderson et al. [2001] in
order to study the plasma characteristics near the sources and the generation
mechanisms for 2fpe emissions, AKR, and other terrestrial wave phenomena. The GEOTAIL and
POLAR Plasma Wave Instruments (PWI) both included sweep frequency receivers
that had an upper frequency limit of 800 kHz and the WlND
WAVES Thermal Noise Receiver (TNR) and Radio Receiver Band I (RAD1) went to 256
kHz and 1024 kHz, respectively. Anderson et al. [2004] have been able to observe
the majority of the AKR spectrum in better detail than with earlier
instrumentation and have made many important new discoveries concerning
Terrestrial low frequency (LF) bursts, which are a part of AKR observed during
strong substorms. Data from both satellite and
ground-based experiments show that the LF bursts are well correlated with
expansive phase onsets and occur during very geomagnetically-disturbed
periods.
Imhof et al. [2003] compared simultaneous observations of bremsstrahlung
X-rays above 2 keV from the Polar Ionospheric
X-ray Imaging Experiment (PIXIE) on the POLAR satellite with the frequency
distributions of AKR waves measured with the Plasma Wave Instrument (PWI) on
the GEOTAIL satellite. Various AKR characteristics such as the low- and high-
frequency cutoffs and the frequencies at peak intensity are compared with
various X-ray parameters such as the magnetic local times of emission, the
total intensities, and the spectral shapes. Imhof et
al. [2004] further made comparisons between X-ray (>2 keV)
emissions emanating from the Earth's Northern Hemisphere aurora observed on the
Polar satellite and auroral kilometric radiation
(AKR) plasma wave intensities detected on the GEOTAIL satellite. It is found
that short time-scale variations of the LF-AKR activity often correspond to the
temporal fine structure of the intensity (5-10 min) of X-ray auroral emissions. HF-AKR intensity enhancements generally
precede enhancements of the X-ray emissions, while the LF-AKR intensity
enhancements generally lag the X-ray enhancements.
The
propagation characteristics of auroral kilometric
radiation (AKR), the propagation mode, power flux as well as propagation
direction, have been analyzed by applying the wave distribution function method
to the Poynting flux measurement data of the Akebono
satellite. Hosotani et al. [2001] showed that the
power flux of O-mode waves was about 10% of the X-mode wave intensity in strong
AKR emissions. The X-mode AKR waves tend to fill inside the radiation cone of
an auroral field line, while the O-mode AKR waves
showed two different propagation directions: one was directed to almost 90
degree with respect to the local magnetic field and the other showed the
propagation angle of about 40 degree. From the above results, they concluded
that the source locations of the O-mode AKR waves with the above propagation
angle located close to the source of the intense X-mode AKR waves.
It is well known that auroral
kilometric radiation (AKR) is intensified during substorms
and has a good correlation with AE index. In the case of the magnetic storms,
however, AKR characteristics have not been investigated. Morioka et al. [2003] report
unexpected behavior of the storm-time AKR and its related particle
precipitation: (1) AKR often disappears in the initial and main phases of the
magnetic storms in spite of the large enhancement of AE index and field-aligned
current, (2) At that time, the energy spectra of precipitating electrons do not
show signature of the field- aligned acceleration but hot electron injection,
(3) The radiation activates strongly in the recovery phase, and (4) AKR tends
to disappear in larger storms. These results suggest that the field-aligned
electric field which accelerates precipitating electrons and drives
field-aligned currents is not formed in the initial and main phases of magnetic
storms.
Kumamoto
et al. [2001] studied the seasonal variations of AKR activities and up-flowing
ion (UFI) events based on long-term plasma wave and particle data obtained by
the Akebono satellite. The analysis results suggested that field-aligned
potential drops vary depending on the seasons and cause AKR seasonal
variations. Furthermore, Kumamoto et al. [2003a] have investigated seasonal and
solar cycle variations of AKR and UFI. In the summer polar region, the peak of
the vertical distribution of the occurrence probability of AKR sources is at an
altitude higher than 5000 km with a value of 10% in the solar maximum period
and at an altitude of 5000-6000 km with a value of 40% in the solar minimum period.
The AKR and UFI occurrence probabilities decrease with increasing solar EUV
ionization in the ionosphere. Kumamoto et al. [2003b] have derived long-term
variations of ambient plasma density in the auroral
regions from whistler wave data, and discussed as a control factor of solar
cycle variations of field-aligned potential drops and AKR sources. AKR
occurrence maximum coincides not with solar wind dynamic pressure peak, but
with sunspot number and F10.7 minimum. UFI events and ambient plasma density
also show similar behavior.
Shinbori et al. [2003a] showed that the plasma
wave data from 263 satellite passages covering the SC onsets included 85 cases
of AKR enhancement within a frequency range from 100 kHz to 1.2 MHz. The start
time of the AKR enhancements tended to occur after the SC onsets determined by
using the geomagnetic records of the Kakioka Magnetic
Observatory within a time range from 3 to 8 minutes. The averaged time is about
5.26 minutes. Based on the delay time feature, the magnetic disturbances
associated with SCs were thought to propagate from
the dayside magnetosphere to the nightside tail
region where they compressed the plasma sheet.
The
second harmonic wave properties of AKR were investigated by using the plasma
wave data of the Akebono satellite. The statistical analysis results by Hosotani et al. [2003] showed that the probability of a
harmonic event occurrence is more than 60% of all AKR events, whose
relationship between the frequencies of the fundamentals and the second harmonics
is exactly two times for the upper and lower cut-off frequencies of the spectra
as well as the fine structures. They showed that the intensity ratio of the
second harmonics to the fundamentals exhibits a two-fold nature, with both a
linear and a quadratic relationship. Furthermore, the second harmonic waves of
the X-mode of AKR are generated from a source which is identical to that of
fundamental waves of the O-mode. These data analysis results suggest that
possible generation mechanism of AKR harmonic structure should allow the
coexistence of different AKR emission processes.
Characteristics of type III solar radio bursts are studied
by Kasahara et al. [2001] using high-frequency
resolution of the SFA of the PWI instrument on board the GEOTAIL spacecraft.
Abnormal type III bursts which have separated frequency bands or have prolonged
tails at particular frequencies are often observed. These observations provide
observational clues to detect density inhomogeneities
in the upstream interplanetary medium. They propose possible models of
interplanetary density structures which can account for some type III
structures observed.
Murata et al. [2004a] studied the Auroral kilometric radiation(AKR) occultations
in the vicinity of the Earth using two observations by GEOTAIL and POLAR. They
compared the dynamic spectra of both satellites for eight months paying
attention to times and frequencies at which AKR is observed simultaneously.
Then, we carefully examined the AKR illumination regions using the POLAR
two-month orbit data. Two distinct regions where the AKR is occulted are found
during the period. One is the region on the night side of the Earth, where the
AKR does not propagate at frequencies > 400 kHz. The other region is in the
vicinity of the plasmapause, on both the day and
night side of the Earth.
Long-term
data analysis results of the seasonal variations of AKR activity by Kumamoto et
al. [2001] suggested that field-aligned potential drops varies depending on the
seasons. The idea was supported by Kumamoto et al. [2001], which clarified the
similar seasonal variations of upflowing ion (UFI)
events. Furthermore, Kumamoto et al. [2003a] have discovered the solar cycle
dependence of vertical distribution of AKR sources and UFI events: AKR and UFI
are quiet during solar maximum while they become active during solar minimum.
By Kumamoto et al. [2003b], long-term variations of ambient plasma density in
the auroral regions has been derived from whistler
wave data, and discussed as a control factor of solar cycle variations of
field-aligned potential drops and AKR sources.
By
using their model to explain the production of
modulation lanes in the dynamic spectra of Jupiter's decametric
emission and the analysis of the curvature of the modulation lanes, Imai et al.
[2001] have obtained the cone half-angle of the emission for the Io-B source.
Their results show that the value of the cone half-angle remains at a fixed
value of 60 degrees for each of the storms analyzed and that the longitude of
the intersection of the active magnetic flux tube with the equatorial plane
increased linearly with time. Imai et al. [2002] used the model with newly
available data to test the model and to measure emission source and beam
parameters. This measurement is consistent with the long-held idea that the
sources Io-B, Io-A, and non-Io-A are due to the same rotating hollow-cone beam
and that the only difference between the latter two is the intensification of
Io-A radiation by the connection with Io in comparison with that of non-Io-A.
The characteristics
of the Jovian Anomalous Continuum (JAC) in
interplanetary space and in the magnetosheath are
investigated using Ulysses observation. Morioka et al. [2004] obtained some new
source characteristics of JAC in addition to those found in previous works.
They also evaluate possible sources of JAC and hypothesize that its origin is Langmuir waves excited at the magnetopause by energetic
particles such as QP bursts ejected from the polar magnetosphere. The relation
of magnetospheric disturbances to the generation of
JAC is also discussed.
Morioka
et al. [2002] investigated the persistence of the most intense Jovian decameter bursts observed during 17 consecutive
years (1974 - 1990). The results showed that even the most intense group of decametric storms lasted only one-earth-day or less. When
it is assumed that the persistence of the Jovian decametric radio storms indicate the duration of the Jovian magnetospheric
disturbance, the result implies that even the large Jovian
magnetospheric disturbance appears in a major
singular event without sequential activities. From this argument, it would be
supposed that the Jovian magnetosphere unloads the
stored magnetospheric energy in a burst and has no
geomagnetic storm-like disturbance.
The dynamic behavior of
electrons with energies from a few tens keV to a few MeV and its relation to plasma waves were examined, using
the data from the NOAA and EXOS-D satellites during the November 3, 1993
magnetic storm [Miyoshi et al., 2003]. After the late main
phase, relativistic electron flux started to recover from the heart of the
outer radiation belt, where the cold plasma density was extremely low and
intense whistler mode chorus emissions were detected. The phase space density
showed a peak in the outer belt, and the peak increased gradually. The
simulation of the inward radial diffusion process could not reproduce the
observed energy spectrum and phase space density variation. On the other hand,
the simulated energy diffusion due to the gyroresonant
electron-whistler mode wave interactions, under the assumption of the Kolmogorov turbulence spectra, could generate the
relativistic electrons without the transport from the outer region.
Krasovsky et al. [2002] studied the dynamics of high energy
electrons in gyroresonance with a quasi-monochromatic
circularly polarized whistler mode tracing a geomagnetic field line are studied
numerically. The space-time
dependence of the electromagnetic field manifests itself in the existence of an
approximate invariant of the electron motion. Under the conditions characteristic of
the magnetosphere, this invariant is found to be conserved with very high
accuracy even in the process of resonant wave-particle interaction, whereas the
constancy of the electron magnetic moment is strongly violated in the
resonance.
Ishisaka et al., [2004] investigated that the
relationship between the GEOTAIL spacecraft potential and the electron number
density determined by the plasma wave observations in the solar wind and
broader magnetosphere (except for the high-density plasmasphere)
and obtained an empirical formula shown by the relation between them. Using
this empirical formula and plasma particle measurements, they have shown the
distribution of low-energy plasma in the magnetosphere.
Goto et al., [2002] proposed a method to
determine the global plasma profile in the plasmasphere
from the satellite observation data. They adopted a stochastic model to
represent the distribution of plasma. In the model, the parameters were
determined by ABIC (Akaike Baysian
Information Criterion) deduced from observed wave data. The validity of our
method was evaluated using simulated data and it was found that the given
distributions were successfully reconstructed by smoothing the observation data
appropriately.
A
determination method of plasmaspheric electron
density profile has been developed by using OMEGA signals observed by the
Akebono satellite. The wave parameters of the signals reflect the density along
the propagation paths and can be calculated theoretically by ray tracing if the
density profile is given. Thus the profile is reconstructed by model fitting so
that the observed and theoretical wave parameters are consistent with each
other. A novel algorithm based on this method was proposed, in which stochastic
factors were taken into account. Goto et al., [2003]
proposed a technique to separate the effects of ionosphere and plasmasphere to the wave parameters in this algorithm and
apply it to some observational data of Akebono. The result for a recovery phase
of a geomagnetic storm reveals the global compression and refilling clearly. In
the other example, the method is applied to examine the symmetry of the plasmaspheric profile. Then Goto
et al., [2004] have improved the method in order to deal with nonducted whistlers which are one of the most typical VLF
wave in the plasmasphere. The nonducted
whistlers originate from atmospherics, and the occurrence probability at an
observational satellite is higher than that of Omega signals.
In
order to determine the propagation mode of Jovian decametric radiation (DAM), Nakajo
et al. [2001] instrumented the long range baseline interferometer and examined
the stability of the phase information to the interferometry
system. In the long baseline interferometer observation, it has been well known
that the observed fringe phases are fluctuated by the temporary variation of
TEC (Total Electron Contents). The dual frequency interferometer method is a
powerful method to eliminate the influence of TEC; however, the problem caused
by the dependence of the linear equations must be considered in the case of the
observation of Jovian decametric
radiation.
S-burst
phenomena of DAM are investigated by Oya et al.
[2001a], who reported that dynamic spectra of the S-bursts are obtained by
using a high time resolution radio spectrograph with a time resolution of 2 ms
and a bandwidth of 2 MHz. Within the occurrence feature of 65 S-burst events
observed in the period from 1983 to 1999, 26 events have been identified as the
S-N burst events, which are characterized by the interaction between the
S-burst emissions and the Narrow band emissions.
Oya et al. [2001b] have developed array
antenna system and multi-frequency interferometer network to investigate the
electromagnetic radiation process in the Jovian
magnetosphere. To understand the energy source and the radiation process of DAM
with correlation to the Jovian auroras,
ionosphere-magnetosphere couplings and interactions with satellite Io, it is
important to obtain the information on the source location and the polarization
of DAMs. The array antenna system consists of 9
antennas covering a frequency range from 20 MHz to 30 MHz. The new long
baseline interferometer system employs the multi-frequency interferometer
method by which ionosphere scintillation effect can be largely reduced.
In
the dynamic spectra of the S-N burst, Oya et al.
[2002] found the trend of emissions with negative and slower frequency drift
named as "Trailing Edge Emission (TEE)", which are often observed
shortly after the appearance of the S-burst. Detailed analyses of these
phenomena revealed that the TEE is not a manifestation of S-burst with slower
drift rate but a variation of N-burst. The results suggested that S-burst and
the associated TEE are formed simultaneously started from a common region with
different drift rates.
Oya and Iizima
[2003] proposed a new method for detecting the phase difference of cesium
frequency standards facilitated at coupling stations of an interferometer of
100km range baselines for observations of decameter wavelength radio waves. The
feasibility of the proposed method has been verified by applying the method to
observations of a 100km range baseline interferometer for decameter wavelength
radio waves at
Hashimoto et al., [2003] developed a software wave
receiver utilizing a programmable down converter (HSP50214B) and a digital data
processor (TMS320C31) to obtain the spectra and waveform of plasma waves in
wide frequency ranges of ELF, VLF and LF bands with high frequency and time
resolution. They reported the successful flight test by using the SS520-2
rocket experiment on Dec. 2000 launched from Ny-Alesund
in
Tsutsui [2002] developed a newly developed system for measuring electromagnetic
(EM) environment in the earth to detect the earth-origin electric pulses which
were leaking out of the ground. The author reported that intensity of the
electric pulses detected above the ground was weaker than those in the earth.
Computer simulations of the self-consistent nonlinear
evolution of electrostatic and electromagnetic 2fp waves excited by
electron beams with electromagnetic particle code have been carried out by Kasaba et al. [2001]. Their results showed that in both
one- and two-dimensional periodic systems an electrostatic 2fp wave
is generated at twice the wave number of forward propagating Langmuir waves by wave-wave, while the electromagnetic 2fp
wave is only excited in two-dimensional systems.
Kasaba et al. [2004]
studied several topics related to the 2fp radiation generated in the
terrestrial electron foreshock. They present a summary of the generation
mechanism of electrostatic and electromagnetic 2fp waves and the electron
acceleration at the quasi-perpendicular shock.
Omura et al. [2003]
have studied the response of thermal plasmas to an induction electric field via
one-dimensional particle simulations. Because of acceleration of electrons and
ions in the opposite directions, there arise counter streaming electrons and
ions that cause the Buneman instability. hey found
that the induction electric field can form an electron beam along the magnetic
field line.
Matsukiyo et al. [2004]
succeeded in reproducing the high-frequency electric wave spectra observed in
the auroral upward current region by one-dimensional
particle-in-cell simulations. Using distribution functions suggested by the
measurements, they found that in the nonlinear state, ion acoustic waves and
electron two-stream (Langmuir) waves dominate the
spectrum. In the absence of cold electrons, electron acoustic waves are not
excited initially but appear only at a late time. This is due to the result of
the formation of a two-temperature electron plasma by nonlinear interactions
when all other instabilities have saturated.
Deng et al. [2004] have provided possible evidence of
multiple X lines collisionless reconnection in the magnetotail at the microscopic level by combining the
observations of plasma, magnetic field, particles, and waves. On
Whistler-mode wave-electron interactions constitute an
important physical mechanism in the Earth’s magnetosphere and the radiation
belts of the magnetized planets. Omura and Summers [2004] performed an electromagnetic
particle simulation to confirm analytical results for the growth rate of
whistler-mode waves in a relativistic bi-Maxwellian
plasma with given temperature anisotropy.
Okada et al. [2001] evaluated the propagation characteristics of ELF and VLF
electromagnetic waves in the Martian ionosphere, and discussed the possibility
for the detection of Martian atmospherics by NBOZOMI observation.
To investigate the occultation of auroral
kilometric radiation (AKR) in the vicinity of the Earth, the dynamic spectra
from GEOTAIL and POLAR satellites are compared by Murata et al. [2004a]. They
reported two distinct regions of AKR occultation, where are the night side of
the Earth and vicinity of the plasmapause.
In collision-free magnetized plasma the solution
of the wave equation becomes singular and unstable. To cope with this problem,
Takano et al. [2003] developed an integral approximation method. By applying
this technique to the mode coupling from a Z mode to an L-O mode in space
plasma, they evaluated the mechanism of wave energy absorption at the resonance
point.
In order to investigate detailed space and time
evolution of elves, Nagano et al. [2003b] computed rigorously propagation in a
magnetized ionosphere of EM pulses radiated by lightning current strokes, by
using a full-wave analysis. Computed results showed that an optical ring is
created at the altitudes of 85-100 km above the lightning, quickly expanding
horizontally over 200 km within < 1 ms, which is consistent with the actual
observation of elves.
Ozaki et al. [2004] computed rigorous wave
intensities on the ground surface and in the ionosphere caused by earthquakes,
by using the full-wave analysis. The computed results in the frequency range
from 10 Hz to 10 kHz showed the difference in spatial distributions of the wave
intensities due to the whistler-mode propagation in the ionosphere.
Hikishima et al. [2004]
investigated the cyclotron resonance and pitch-angle diffusion of the resonant
electrons, to analyze the generation mechanism of the chorus emissions. Their
results indicated that the initially large pitch-angle anisotropy of the
resonant electrons is rapidly pitch-angle diffused by a generated whistler mode
wave, and the pitch-angle anisotropy decreases down to the small anisotropy
which saturates wave growth.
Ikeda [2002] examined the possibility of the
sideband wave generation in whistler-mode via a non-linear Doppler-shifted
cyclotron resonant interaction between untrapped
electrons and the whistler mode carrier signal by using a new equation system.
The untrapped electrons resonant with the
quasi-monochromatic whistler mode signal are phase-bunched with the trajectory
gap, just outside the separatrix, on the phase space
in the frame of electron of the Doppler-shifted cyclotron resonance with the
carrier. Then, they may be able to radiate the whistler mode sideband waves
with frequencies of fundamental, second and third harmonics, whose currents may
never be zero because of strong non-linear interaction. It is imagined that, at
the same time, two kinds of plasma may interact with the carrier signal to form
the broadening, and with the sideband waves showing frequencies of fundamental,
second and third harmonics. The fundamental, second and third harmonics
sideband wave frequencies may be related to the saturated amplitude of the
carrier signal.
Nishimura
et al. [2002] studied the acceleration and heating of electrons at
quasi-parallel shock waves by means of a one-dimensional full particle computer
simulation. Their simulation shows that the ion beam instability due to the
anomalous cyclotron resonance excites whistler mode waves in the upstream
region. The electron acceleration
parallel to the magnetic field results from the parallel electric fields caused
by both the whistler mode waves and the electrostatic shock potential. They
found that the contribution of the whistler waves to the parallel acceleration
is as important as that of the electrostatic shock potential below the critical
Mach number.
The
properties of reformation in perpendicular collisionless
shocks were investigated by Nishimura et al. [2003] using one-dimensional
particle-in-cell simulation. The reformation is known to be associated with ion
reflection at the shock ramp and subsequent ion gyromotion
in the upstream region. However, it
is also known that the shock reforms intermittently at sufficiently high Mach
number if ions are reflected continuously at the ramp. The simulations were performed to
investigate this issue and they found that the shock potential changes
dramatically through the re-formation cycle, so that the potential variation
leads to the intermittent response of the shock.
Hada et al. [2003] analyzed the shock front nonstationarity of perpendicular shocks in super-critical
regime by examining the coupling between "incoming'' and "reflected''
ion populations. For a given set of parameters including the upstream Mach
number and the fraction alpha of reflected to incoming ions, a self-consistent,
time-stationary solution of the coupling between ion streams and the
electromagnetic field was sought.
The analytic results were in good agreement with full particle
simulations for low beta case.
Futaana et al. [2003] studied the nonthermal ions which were measured by Particle Spectrum
Analyzer/Ion Spectrum Analyzer (PSA/ISA) on board the Nozomi
when the spacecraft was very close to the Moon. It was found that the nonthermal ions were protons and had a partial ring
structure in the phase space. By
conducting particle tracing calculation, their source location was found to be
the dayside of the Moon, and the nonthermal ions seem
to have large velocities when they were generated. It was proposed that the
electromagnetic field in the vicinity of the Moon must have a dynamic
structure, possibly a miniature bow shock associated with a local magnetic
anomaly, where some of the solar wind protons are deflected to forms a partial
ring structure in the velocity phase space.
Cross field diffusion of energetic particles (cosmic rays)
in a two-dimensional static magnetic field turbulence is studied by Otsuka and Hada [2003] by
performing test particle simulations. Qualitatively different diffusion
processes were observed depending on the ratio of Larmor
radius to the correlation length of the magnetic field fluctuations. The
diffusion was found to be composed of several regimes with distinct statistical
properties, which can be characterized using Levy statistics.
Lembege et al. [2004] published a review to address a subset of
unresolved problems in collisionless shock physics
from a theoretical and/or numerical modeling point of view. The topics are the nonstationarity of the shock front, the heating and
dynamics of electrons through the shock layer, particle diffusion in turbulent
electric and magnetic fields, particle acceleration, and the interaction of
pickup ions with collisionless shocks.
Supra-thermal particle acceleration for a perpendicular magnetosonic shock was discussed by Hoshino [2001] by
focusing on the interaction of particles with a large amplitude solitary wave
formed in the shock front region/shock transition layer. The author showed that
the shock surfing acceleration in a relativistic electron-positron shock occurs
under the interaction of the trapped particles by the magnetosonic
solitary wave with the shock motional electric field, and that the trapped
particle can be efficiently accelerated up to the shock potential energy
determined by a global shock size.
Hoshino and Shimada [2002] studied the suprathermal
electron acceleration mechanism in a perpendicular magnetosonic
shock wave in a high Mach number regime by using a particle-in-cell simulation,
and found that shock surfing/surfatron acceleration
producing suprathermal electrons occurs in the shock
transition region, where a series of large-amplitude electrostatic solitary
waves ( ESWs) are excited by Buneman
instability under the interaction between the reflected ions and the incoming
electrons.
Hoshino and Mukai [2002] found
that the energy spectrum of electrons in magnetic reconnection has a suprathermal population above a few keV,
and more importantly the higher energy spectrum can be fitted by exp(-αv).
A simple model to explain the suprathermal electrons
based on a Fermi acceleration process was proposed.
Shimada and Hoshino [2003] investigated the electron-ion
coupling process under Buneman instability between
inflow electrons and reflected ions in the shock transition region. The study
examined how electron holes affect the ions and interact with them. This study
may provide a first indication of what regulates strong electron heating in the
shock transition region through the coupling process between the electrons and
ions. Shimada and Hoshino [2004]
evaluated the effect of the frequency ratio omega(pe)/Omega(ce) on the electron energization
in the shock transition region by using periodic simulations with realistic
mass ratio. Their results showed that when omega(pe)/Omega(ce) is less than or equal to 1 no electron phase space hole
is generated and when omega(pe)/Omega(ce) is greater than or equal to 10 a clear series of
electron phase space holes is generated.
Trakhtengerts et
al. [2002] developed the kinetic theory for runaway electrons in a stochastic
electric field. The general kinetic equation for the isotropic part of the
electron distribution function was derived and was simplified to the
differential form for a particular case of electric field spectral intensity.
The stationary analytical solution and numerical dynamic solutions were
obtained and were discussed in connection with the problem of energetic
electrons in a thunderstorm cloud.
Electron acceleration by a stochastic (in space) electric
field in the atmosphere was considered by Trakhtengerts
et al. [2003a] taking into account limited scales of the acceleration layer.
Stationary solutions of the kinetic equation in a finite layer were analyzed
numerically in the presence of source of energetic electrons. These solutions
were discussed in connection with γ- and x-ray emissions observed inside
thunderclouds.
A role of the second-order cyclotron resonance
effect in the self-consistent approach to the problem of triggered ELF/VLF
emissions was estimated by Trakhtengerts et
al. [2001].The main and general conclusions are: (1)
The second-order cyclotron resonance effects give an important contribution to
triggered ELF/VLF emissions. (2) The short pump whistler wave packets generate
fallers, while the long packets generate predominantly rising tones. (3) There
are critical maximal and minimal values for the pump wave pulse duration.
Trakhtengerts et
al. [2003b] considered the effect of initial phase
bunching of energetic electrons on the generation of triggered ELF/VLF
emissions in the magnetosphere. They focused on a phase-bunched beam in the
velocity space, which serves as a traveling-wave antenna emitting secondary
waves, and showed that the antenna field is significant as the seed wave which
is further amplified by the same beam via the cyclotron resonant mechanism.
Electron accelerations in the outer radiation belt was
investigated based on the Akebono observations by Obara
et al. [2001]. Increase of the electron flux occurred in low L region and in
low energy. Phase space density for MeV electrons had
a peak around the center of the outer radiation belt. This means the internal
acceleration took place in the outer radiation belt
during the storm recovery phase.
Obara and Li [2003] showed that MeV electrons moved
Earthward quickly with a sudden commencement, filling the so-called the slot
region, and that the electron flux decayed slowly, forming the slot structure
again. Time constant of the decay was studied.
Miyoshi et al. [2003]
examined the dynamic behavior of electrons with energies from a few tens keV to a few MeV and its relation
to plasma waves, using the data from the NOAA and EXOS-D satellites during the
November 3, 1993 magnetic storm, and then numerically investigated the electron
acceleration process at the storm. Their study suggested that the acceleration
by whistler mode chorus via gyroresonant
wave-particle interactions outside the plasmapause
could play an important role to generate the storm-time relativistic electrons.
Katoh et al. [2003]
studied particle acceleration processes due to wave particle interactions by
employing numerical simulations based on a hybrid algorithm in order to
investigate the merging process of cometary oxygen
ions into the solar wind and verify a elementary process of energizing
mechanism of relativistic electrons in the outer radiation belt during a
geomagnetic storm recovery phase.
Krasovsky et al. [2003] studied the electrostatic pulses recorded
by the GEOTAIL spacecraft and labeled electrostatic solitary waves (ESW) within
the framework of Bernstein-Greene-Kruskal (BGK) solitons. The general approach developed in the article
applies to arbitrary particle distributions of the background plasma,
velocities of the BGK solitons and wide variety of
the recorded ESW waveforms. The new models and physical interrelations reveal
universal features of the BGK soliton structure and
allow a direct juxtaposition with the observations. The established
interconnections between the physical characteristics of the waves agree well
with the GEOTAIL data on ESW waveforms.
Krasovsky et al. [2004] clarified the
qualitative differences between the actual three-dimensional (3-D)
perturbations and the well-known 1-D Bernstein-Greene-Kruskal
(BGK) modes of the electron hole type. They showed that the anisotropy caused
by the geomagnetic field is a decisive factor and the hole-like structures is
closely connected with the quasi-one-dimensional nature of the electron motion,
predominantly along the external magnetic field.
The formation process of ESW was studied by Umeda et al. [2002]. They conducted one- and
two-dimensional electrostatic particle simulations with open boundaries. In the
open system, spatial structures of electron holes vary depending on the
distance from the source of the electron beam. A lower hybrid mode is excited
locally in the region close to the source of the electron beam through coupling
with electron holes at the same parallel phase velocity. The lower hybrid mode
modulates electron holes excited in later phases, resulting in formation of
modulated one-dimensional potentials.
Umeda et al. [2004]
extended the previous electrostatic particle model to an electromagnetic
particle model. In the present two-dimensional simulations of an electron beam
instability, electromagnetic field components are enhanced around
two-dimensional electron holes. They found that the enhancement of
electromagnetic fields is due to a current formed by electrons undergoing the E
× B 0 drift, where the electric field is a perpendicular
electrostatic field at the edge of a two-dimensional electron hole. An
electromagnetic beam mode is excited by the current due to the drifting
electrons moving with the electron hole.
Generation
of electrostatic multiple harmonic Langmuir modes
during beam-plasma interaction process has been observed in laboratory and spaceborne active experiments, as well as in computer
simulation experiments. Despite earlier efforts, such a phenomenon has not been
completely characterized both theoretically and in terms of numerical
simulations. Yoon et al. [2003] found analytic expressions for harmonic Langmuir mode dispersion relations and compared their
results with numerical simulation results.
Gaelzer et al. [2003] developed generalized
weak turbulence theory in which multiharmonic
Langmuir modes were included and the self-consistent
particle and wave kinetic equations were solved. The result shows that harmonic
Langmuir mode spectra exhibit a quasi-power-law
feature, implying multiscale structure in both
frequency and wave number space spanning several orders of magnitude. The generation of harmonic Langmuir modes during beam plasma interaction was studied
by Umeda et al. [2003] with nonlinear theoretical
calculations and computer simulations. In their Vlasov
simulation code, multiple harmonic Langmuir modes up
to 12th harmonics can be included in contrast to previously available
simulations which were restricted to the second harmonic only. The
frequency-wave-number spectrum obtained by taking the Fourier transformation of
simulated electric field both in time and space showed an excellent agreement
with the theoretical nonlinear dispersion relations for harmonic Langmuir waves. The saturated wave amplitude features a
quasi-power-law spectrum which reveals that the harmonic generation process is
an integral part of the Langmuir turbulence.
A linear
analysis and 2-1/2dimensional electromagnetic full-particle simulations were
performed by Fujimoto and
Shklyar and Matsumoto [2002] studied the initial problem of
plasma wave dynamics in the presence of a sharp density jump that divides the
space into transparent and opaque regions. A wave packet was assumed to be
initially localized in the transparent region. The transient process of field penetration
beyond the density barrier during the wave packet reflection from the density
jump was investigated.
In order
to self-consistently study the kinetic processes at the Venus ionopause, Terada et al. [2002] calculated the Venus ionopause-solar wind interaction region kinetically,
including the ionosphere, ionopause transition layer,
magnetosheath, and solar wind, by applying
boundary-fitted coordinates to the particle-in-cell code. They found that the
distribution of ionopause surface waves generated by
the Kelvin-Helmholtz (K-H) instability exhibits a
clear asymmetry between hemispheres of upward and downward solar wind motional
electric fields. Accordingly, the asymmetrical momentum transport across the ionopause yields an asymmetrical convection pattern of the
ionosphere. Terada et al. [2004] extended their work to study a viscous process
associated with the K-H instability around the ionopause,
which is less well understood compared to the pickup process of exsospheric ions and electrons. They studied the relative
importance of the escape processes for the case of low solar wind dynamic
pressure as well as for the high dynamic pressure case, and showed the viscous
removal process occurring at the ionopause plays a
significant role in the ion escape from Venus.
A merging process of cometary
oxygen ions into the solar wind particle was studied by Katoh
et al. [2003] employing numerical simulations based on a hybrid algorithm. The results of one-dimensional hybrid
simulation shows that a spatial extent of interaction region surrounding comet
nucleus is deeply related to the ion beam instability driven by a field aligned
motion of picked-up ions. Katoh and Omura [2004] studied
resonant interaction between relativistic electrons and whistler mode waves excited
by a temperature anisotropy using the hybrid simulation. The simulation shows that selected resonant electrons are effectively
accelerated in a homogeneous system where both forward and backward traveling
waves interact with the relativistic electrons.
Matsukiyo and Hada [2002] studied a
long time evolution of cyclotron maser instability at null wave number (k=0)
which is destabilized by relativistic ring distribution of plasma through the
cyclotron resonance. They performed
particle simulations using a plasma which consists of gyrotropic
or nongyrotropic relativistic ring electrons,
background positrons, and background electrons. The linear theory predicts
that, when the initial ring energy is strongly relativistic, there appears a
critical initial ring momentum at which the system is marginally stable.
Numerical simulations show, however, that the system is nonlinearly unstable
even when the initial ring momentum exceeds the critical momentum.
Matsukiyo and Hada [2003] examined
the dispersion relation and nonlinear evolution of the parametric instabilities
of circularly polarized Alfven waves in a relativistic electron-positron plasma. First, the
nonlinear dispersion was solved in a nonrelativistic
limit, then the weakly relativistic effect was examined. The one-dimensional
full particle simulation and bicoherence analysis of
the simulation result suggest that successive decay via the interaction between
the parallel propagating Langmuir-like wave and antiparallel propagating Alfven-like
wave can efficiently generate a continuum of low frequency electromagnetic
waves, which can interact with energetic particles.
Using topside sounder data obtained by the Ohzora (EXOS-C) satellite, Uemoto
et al. [2004] investigated the structure and dynamics of the ionization ledge
in the equatorial topside ionosphere. They found that the ionization ledge
observed in the local
Usui et al. [2004a,
2004b] for the first time applied electromagnetic PIC (Particle-In-Cell)
computer simulations to analyze the antenna characteristics in magnetized
plasma. They particularly examined the electron kinetic effects on the antenna
impedance. It is confirmed that the most obvious resonance point is the local
Upper Hybrid Resonance frequency. As the electron temperature increases, the
resonance frequency also increases in accordance with the modification of
dispersion relation for the UHR branch.
Numerical simulations on active perturbation of space
environment by microwave power transmission (MPT) and plasma beam emission for
the spacecraft charging control have been performed. Usui
et al. [2002] studied a three-wave coupling process occurring in an active
experiment of MPT in the ionospheric plasma by
performing one dimensional electromagnetic PIC (Particle-In-Cell) simulations.
Continuous emission of intense electromagnetic waves from an antenna located at
a simulation boundary excites a low-frequency electrostatic wave as the result
of a nonlinear three-wave coupling.
Usui et al. [2004c] also studied the basic
process of the spacecraft charging and its neutralization using dense plasma
emission by performing PIC simulations.
They particularly examined the electron/ion flux to the charged body and
the corresponding potential variation. It is shown that the negatively charged
body is neutralized mainly by the enhancement of ion flux of the emitted plasma
In the transient process of the charge neutralization, they found very
turbulent current variation at the emitted plasma cloud region, which may cause
electromagnetic perturbation in the vicinity of the body.
One of the most important methods for the studies of
plasma waves observed by spacecraft is to compare them with other observations
either with same spacecraft or with other spacecraft. Simultaneous ground-based
observations also help our understandings of the plasma wave generation
mechanisms. Murata [2003] and Murata et al. [2002a] have constructed a software
system (STARS) to gather observation data files individually managed at several
organizations. It also provides a variety of functions to plot and analyze the
data. For 3-dimensional data analyses of the observation data, a virtual
Earth’s magnetosphere system (VEMS) is produced by Murata et al. [2004b]. Murata et al. [2002b],
Murata et al. [2002c], Murata [2002d] and Murata et al. [2002e] have developed systems to achieve
high-performance computing and to support computer simulations for plasma
particle simulations.
Akimoto et al. [2003] developed a new general-purpose
computational technique for classifying the plasma waves in a systematic way
from database of scientific satellite. Firstly, they propose a two-step cluster
analysis for the classification. Applying this cluster analysis to the key
parameters of the Akebono wave data, they could make some representative
classes of wave phenomena with a small amount of calculation time. In order to
determine the suitable number of representative class, they propose an
evaluation function with AIC.
Finally, they discriminated to the representative classes and exception.
Kasahara et al. [2002]
introduced new computational techniques for extracting the attributes and/or
characteristics of the plasma waves and particles from the enormous scientific
database. These techniques enable us to represent the characteristics of
complicated phenomena using a few key-parameters, and also to analyze large
amount of datasets in a systematic way. These techniques are applied to the
observational data of the ion heating/acceleration phenomena in the auroral region obtained by the Akebono satellite.
Tanaka et al. [2004] developed a general-purpose system
which manages and provides various kinds of information accumulated in their
university. One of the most important points in the design of the system is
management of the enormous amount of data, which comes up to several tera-bytes in the field of natural science in some cases.
They constructed a database system on the geospace
radio environment obtained by the Akebono satellite.
The
lunar radar sounder (LRS) experiment onboard SELENE (SELenological
and ENgineering Explorer) has been planned for
observation of the lunar surface and subsurface structures. The computer
simulation of the LRS observations and development of data analysis method have
been performed by Kobayashi et al. [2002a] using newly developed simulation
code, Kirchhoff approximation sounder simulation (KiSS) code. It has been shown by the simulation that the
subsurface echoes are detectable by using data stacking technique. Kobayashi et
al. [2002b] has also performed the simulation of the LRS observations in the
lunar highland regions, where subsurface echoes are severely masked by
confusing surface echoes. The application of the synthetic aperture radar (SAR)
method for subsurface echo analysis in the lunar highland region has been
proposed based on the simulation results.
As for the effective method for
EMC of spacecrafts in space plasma, Okada et al. [2004] demonstrated the sheilding effects of the conductive hood covering the solar
sensor onboard NOZOMI spacecraft by performing a series of FDTD simulations
with different configurations of a conductive hood.
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for Solar-terrestrial Physics Observation Data”, IPSJ Trans. on Databases,
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Murata, K. T., Hiroko O. Ueda, K. Ueoka, H. Usui, M. Okada, Y. Omura and H. Matsumoto [2002c], “An Object-oriented Plasma
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Murata, K. T. [2002d], “A Problem Solving
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Murata, K. T. [2003], “A World-wide
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Murata, K. T., Nurdiyana
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Oya, H., and M. Iizima [2003], “Mapping of the decameter radio sources ofCassiopeia
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Acknowledgements
We would like to thank the following
persons for their contributions to this national report of Japanese Commission
H: Masashi. Hayakawa, Hideaki Kawano, Toshihiko Iemori,
Shinobu Machida, Yasumasa Kasaba, Akira Morioka,
Takayuki Ono, Hirotsugu Kojima, Kozo Hashimoto, Hideyuki Usui,
Tadasu Nakamura, Yoshiya Kasahara, Satoshi Yagitani,
Takeshi Murata, and Taketoshi Miyake.