1) sc/si phenomena
Recently, the transient magnetospheric responses to solar wind variations can be sufficiently clarified using high-time resolution data from global network stations. An anomalous geomagnetic sudden commencement was observed at the network stations at 03:41 UT on March 24, 1991. The sc is characterized by an exceptionally large and sharp impulse observed in its initial part along the noon meridian in middle and low latitudes, i.e., 234nT at Kakioka. Araki et al.  analyzed the sc in detail by using high time resolution digital data from the 210 Magnetic Meridian Chain in the west Pacific, Sub-Auroral Magnetometer Network (SAMNET) in the United Kingdom and southern Scandinavia, the EISCAT Magnetometer Cross in northern Scandinavia and Svalbard, and Canopus in Canada together with satellite (COES 6 and 7, CRRES, and GMS) data. An interplanetary shock with an exceptionally steep and large pulse of momentum increase in the initial part of the wave front impacted the magnetosphere on the afternoonside and compressed it rapidly with an averaged velocity of 800-900 km/s. They found that although the delay in the peak time of the main impulse observed on the ground is consistent with ionospheric hydromagnetic wave propagation from the dayside to the nightside with finite speed of several hundred kilometer per second, the initial onset time of the DL pulse on the ground was almost simultaneous everywhere. They suggested the existence of an "almost instantaneous" propagation mode below the ionosphere, i.e. the DL pulse is converted to an electromagnetic wave ducted in the dayside space below the ionosphere and propagates to the nightside causing an almost simultaneous global onset of the DL pulse.
In order to examine which components of DL and DP fields dominate sc and si magnetic variations at low and middle latitudes on the ground, Yumoto et al. [1996b] statistically analyzed 41 events of sc and si magnetic variations observed along the 210 deg. meridian during the 15 months from November 1992 through January 1994 and found that the amplitudes of sc and si at low and middle latitudes are larger in the summer hemisphere than in the winter hemisphere. They also used the 210 deg. MM data to confirm the enhancement of sc and si amplitudes near the dayside equator.
2) Global characteristics of Pi 2s
The latitudinal profiles of Pi 2 amplitudes and phase relations along the 210 deg. magnetic meridian imply that Pi 2 pulsations observed on the ground consist of different five mode oscillations (see Osaki et al. , Shinohara et al. , and Li et al. [1998a, 1998b]). A bouncing of impulsive field-aligned current (and/or a kinetic Alfven wave) between the plasmasheet and the auroral ionosphere (cf. Shiokawa et al. ) and an oscillation of the substorm current wedge are believed to be detected as high- and mid-latitude Pi 2s, while a surface wave excited at the plasmapause and a cavity-like oscillation in the inner magnetosphere are believed to be observed as mid- and low-latitude Pi 2s. Shinohara et al.  further indicated that daytime and nighttime Pi 2 pulsations in the equatorial and low-latitude region can be explained by invoking an instantaneous penetration of electric field variations from the nightside polar to the dayside equatorial ionosphere, and a direct incident of compressional oscillations from the nightside inner magnetosphere [Itonaga et al., 1997a, 1997b, 1998], respectively. The ground Pi 2 pulsations are concluded to be an ensemble of these five modes, which show their own propagations (or timings) and spatial illuminations.
3) Pc 3 magnetic pulsations
Using magnetic field data from the 210 MM chain and the Geotail satellite, Matsuoka et al.  presented the latitudinal structure of a Pc 3 pulsation event that occurred on October 17-18, 1992. During the event, Geotail was located in the dayside magnetosphere at a radial distance of 8 Re and observed tailward propagating fast-mode magnetosonic waves in the Pc 3 band. H-component pulsations observed at the ground stations, also on the dayside, exhibited dynamic spectra similar to those observed from Geotail. Spectral analyses of the ground data revealed that the H-component pulsation amplitude is at an overall maximum at the highest-latitude station of the magnetometer array, but two additional maxima occurred at L~1 and L~2.1.
Tanaka et al. [1998a] investigated global characteristics of H- and D-component Pc 3 pulsations observed along the 210 degree MM magnetometer network from the dip equator to high latitude. They found that the D-component Pc 3's in the prenoon sector 0900-1200 LT at L= 1.2-5.5 show a coherent, in-phase (out-of-phase) oscillation in the northern (southern) hemisphere with respect to the H component Pc 3's at GUA. This result indicates that the D-component Pc 3's in the prenoon sector at L = 1.2-5.5 are closely related to the upstream source waves. The amplitude peak of the H-component Pc 3's at L=2.1 can be explained by the local field-line resonance. The other amplitude peak of the H-component Pc 3's near the magnetic equator may be explained by invoking direct incidence of compressional Pc 3 source waves from the outer magnetosphere.
4) Peculiarities at low latitudes and at the dip equator
A peculiarity of Pc 3 pulsations at low latitudes (< 30 deg.), i.e., increasing period with decreasing magnetic latitude, was demonstrated and compared with the results of numerical models of the magnetospheric resonator by Pilipenko et al. [1998a]. They concluded that daytime ULF observations can be used as a low-latitude extension of whistler observations to monitor plasma density variations in the plasmasphere.
The dip equator is the place at where geomagnetic field line horizontally lies, and is characterized by the high zonal ionospheric conductivity which is so-called "Cowling conductivity". An enhancement of signal amplitude of geomagnetic variations is general character of the dip equator, e.g. EEJ, DP2, the preliminary reverse impulse (PRI), sudden commencement (sc), sudden impulses (si), Pi 2 at the dip equator [Colqui et al., 1998; Yumoto et al., 1996b; Shinohara et al., 1998; Sibeck et al., 1998]. Therefore, the dip equator is a peculiar region where we can easily sense the geomagnetic phenomena.
5) Other hydromagnetic phenomena
Recently, ULF magnetic variations were analyzed to investigate precursors before the onset of earthquakes [Hayakawa et al., 1997] and/or relationship between seismic and electromagnetic activity [Yumoto et al., 1998]. Since these electromagnetic emissions and DC variations must be a promising candidate for short-term prediction of earthquakes, we are in a position that we should accumulate more amount of convincing signatures of earthquakes.
(K. Yumoto: email@example.com)
Shinohara et al.  studied the electromagnetic turbulence in the frequency range from 1 to 10 Hz near the onset site of substorm in the Earth's magnetotail. The Geotail observations by the search-coil magnetometer and spherical double-probe instrument clearly show electromagnetic wave activities in the lower-hybrid frequency range near the onset site, i.e., near the neutral line. The linear and quasi-linear calculations of the lower-hybrid drift instability well explain the observed electromagnetic wave turbulence quantitatively. The calculated time for the electron heating is comparable to the electron time scale of the expansion onset, but that of ion heating is much longer. They concluded that observed wave intensity is not sufficient to support dissipation necessary for the resistive tearing mode instability.
Kasahara et al.  investigated the correlation between the ELF/VLF noise and the electron and ion fluxes at the polar region observed by Akebono satellite. They found that the waves are electromagnetic below the local oxygen cyclotron frequency and they become electrostatic in the higher frequency range. The waves are usually observed in the cusp or along the higher latitude side of auroral oval, and the waves are more intense in the cusp region. The occurrence region extends to lower latitudes when the geomagnetic activity becomes high. They concluded that the primary waves are most likely the ion acoustic waves which are excited by low energy electrons, and that ions are accelerated and heated by those waves showing a clear correlation with the wave intensity.
Hatakeyama et al.  studied particle drifts in a traveling wave with a cyclotron frequency. They found a difference in a particle acceleration between the first half- cycle and the second half-cycle of the Larmor motion. This difference modifies the cyclotron-resonance trajectory, giving rise to particle drifts perpendicular both to the wave propagation and background magnetic-filed lines. A perturbation method in the orbit theory successfully gives analytic expressions and numerical calculations demonstrate the generation of drift. This mechanism is further argued by comparing it with the experimental results conducted with the Phaedrus-B axisymmetric tandem mirror by Hatakeyama et al. .
A formation of the collisionless ion acoustic shocks in a plasma with negative ions was studied by Takeuchi et al. . They found an occurrence of steepening of the positive or negative density jumps depending on the parameter e which is a ratio of negative to positive ion density. For e < ec ( about 0.65 ), positive density jumps evolve into compressive shocks. However, for e > ec, negative density jumps evolve into rarefactive shocks. The value of ec is well explained on the basis of Korteweg-de Vries equation.
(S. Machida: firstname.lastname@example.org)
Matsumoto and Usui  reported the bursts of electron cyclotron harmonic waves observed by Geotail at the dayside equatorial outer magnetosphere region. They call these emissions as "Totem Pole (TP) emissions" after their bursty and harmonic spectral structures. They found that the first harmonic emission of ECH is split into two major parts in the frequency domain. Usui et al.  demonstrated that such TP emissions mainly observed in the dawnside region near the magnetopause in the basis of statistical data analyses.
Excellent collaborations of spacecraft observations and computer experiments have been proceeded in the study of the Electrostatic Solitary Waves (ESW). Since the discovery of the ESW in the plasma sheet boundary by Geotail, extensive efforts to study their generation mechanisms have been made. Omura et al.  surveyed the parametric dependence of the nonlinear evolutions of electron beam instabilities via one-dimensional full particle computer simulations. They showed that the route toward generations of ESW, EQMW, and electron plasma waves strongly depends on the initial electron/ion velocity distributions. Their computer simulations lead to the establishment of comprehensive generation model of ESW, EQMW, and electron plasma waves. Further, Miyake et al.  extend these simulations to two-dimensional system and discussed the time dependence of generated electrostatic potential structures perpendicular to the ambient magnetic field.
In the laboratory experiments for plasmas, the formation of electrostatic potentials have been investigated by Sato et al. . They showed that an extremely large amplitude electron plasma waves are generated by applying an external Radio Frequency (RF) waves to a ring exciter and that steep changes of electron density, temperature and potential along the ambient magnetic field are observed in the region around the wave generation, where the waves are localized because of enhanced wave damping. Such electrostatic potential formation as a result of interaction between RF fields and plasmas attracts much interest in connection with particle acceleration mechanism in space plasmas and plasma confinement in fusion oriented devices.
(H. Kojima: email@example.com)
A. Whistler mode waves (by a sounding rocket and Geotail)
Whistler mode waves are observed in various regions around the Earth.
In the auroral region, Takizawa et al.  reported the LF waves associated with pulsating aurora by a sounding rocket S-520-12 launched from Andoya, Norway. LF waves lagged behind auroral emission by 8 sec. They suggested that the pulsating LF waves were generated by precipitating low energy electrons in the altitude of 2000-4700 km at L=6.7 on which pulsating auroral patch existed.
In the dayside magnetosphere, Yagitani et al. [1996a] studied generation and propagation mechanisms of chorus emissions via cyclotron resonance with energetic particles based on simultaneous wave/particle measurements by GEOTAIL. They computed the cyclotron growth rates and showed that the chorus emissions are most likely generated by the energetic electrons. Nunn et al.  also reported the wave and particle data in the vicinity of the generation regions in the equatorial region at about L=10. Analysis shows that the k vectors are closely parallel to the ambient magnetic field. Based on detailed data, they simulated the observed emissions by a Vlasov simulation code.
In the magnetosheath, Zhang et al. [1998a] studied lion roars by the waveform data of GEOTAIL PWI/WFC. About 30% (type A) of the lion roars are associated with the mirrors waves or the decrease of the ambient magnetic field, while others (type B) are not associated. They found that 5% of them (only type B) seems to be generated locally in the vicinity of the spacecraft for these cases. They are usually observed near the bow shock and very likely the downstream propagating whistlers excited in the bow shock region. Matsui et al.  also reported long-duration whistler waves (LDWW) observed by Geotail MGF. LDWW are band-limited emissions near the lower hybrid frequency typically lasting several tens of minutes. The propagation vectors strongly suggests that the bow shock is the common source. The 'flat-topped' electron distribution function is concurrently observed and is likely to yield a favorite condition for LDWW propagation.
In the upstream region, Zhang et al. [1998b] studied narrowband and short-lived whistlers (NSW) frequently observed by Geotail PWI/WFC. Nearly all the NSW in the electron foreshock propagate in a downstream direction parallel to the magnetic field and must be excited by electron cyclotron resonance. These features suggest the existence of a temperature anisotropy in the upstream electron beam. The competition between electrostatic and whistler instabilities and the finite size of the beams are very likely the reasons of its short life. These NSW can be well explained by a modeled electron beam with a loss-cone distribution in the electron foreshock.
B. Nonthermal continuum radiation (by Geotail)
Nonthermal continuum radiation is generated as a result of mode conversion from the electrostatic upper hybrid waves to the L-O electromagnetic waves. Kasaba et al.  studied the short-lived enhancement of nonthermal continuum radiation generated at the plasmapause from the midnight to dawnside sector. Simultaneous Geotail and Wind observation shows a series of electrons injected at the midnight sector associated with substorm generate both the enhancement and the classical nonthermal continuum. Frequency variation of this radiation reflects the drift motion of injected electrons depending on their injected velocity. Its harmonic structure also indicates the real-time magnetic field strength at the plasmapause so that they statistically studied the variation of the radius of the plasmapause during the substorms.
C. Auroral kilometric radiation (by Geotail/Akebono)
Murata et al.  studied the interrelation between the AKR activities and the well-established measures of substorms. A measure of the AKR activity can be expressed as 'AKR index', proportional to AKR power flux at a given time of the observation. The onsets of substorms are well represented by the sudden increase of the AKR index. Kurth et al.  analyzed AKR observations by Polar and Geotail and compared with auroral electrojet (AE) index. They pointed out the limitations of both the AKR index and the AE index in providing truly global measurements of substorm activity.
Kasaba et al. [1997a] studied the angular distribution of AKR based on a 38-month GEOTAIL PWI observations. The AKR illumination pattern becomes narrower with increasing frequency above 300 kHz. The difference is more evident in the duskside zone and when geomagnetic conditions become more disturbed. They also showed that AKR is more active on the winter hemisphere especially for the higher frequency range. It is confirmed in more detailed study by Kumamoto and Oya . The statistical analyses of AKR observed by the plasma wave and sounder experiment (PWS) onboard Akebono for the 7 years showed clear seasonal variations, the increase of both intensity and occurrence-frequency in the winter polar regions. This asymmetry becomes more prominent in the high frequency range. The origin is plausibly related with the seasonal dependence of the acceleration processes of the auroral electrons.
D. 2fp radiation (by Geotail)
The 2fp electromagnetic radiation is frequently observed in the upstream region of the Earth' bow shock. It is a narrow band emission at twice the solar wind electron plasma frequency.
The remote sensing of 2fp radio source was reported by Reiner et al. . They combined direction-finding data from simultaneous WIND/GEOTAIL observations to provide the first 3-D source location by two spacecraft triangulation. In two cases, the 2fp radio source centroid was located in the upstream wing of the electron foreshock some 10-20 RE from the contact point of the tangential IMF line to the bow shock. Kasaba et al. [1997b] analyzed by other statistical methods. They determined the 2fp radio source location by three statistical methods: mapping of 2fp flux, analysis of bifurcation phenomena with density discontinuity in the solar wind, and statistical direction findings. They showed that the source is generally on the tangential field line but not concentrated around the contact point. More detailed studies including numerical simulations are still in investigation [cf. Kasaba, 1997]
E. Jovian radiation (by Zao observatory and Geotail)
Jupiter is the most radio-active planet, so that Jovian radiation has been observed from ground-based observatories. Misawa et al.  studied polarization of Jovian decametric radiations at Zao observatory of Tohoku University. Most of Io-related events indicate highly right-handed elliptical polarization and slightly more linear polarization than non-Io-A events. They also showed that Io-A and Io-B related events indicate significant difference in their axial ratios.
In 1995, Comet Shoemaker-Levy 9 passed across the Jovian magnetic fields and collided to Jupiter. Enhancement in X-ray and synchrotron radiations suggested non-negligible change in the inner magnetosphere. Oya et al.  reported the Jovian decameter radiation in this period. They showed large enhancement and interpreted as the result by dust-plasma interactions. The enhancement was approximately 10 times of the regular maximum level and continued for 6 months. It suggested that the Jovian plasma environment was completely changed by the dust clouds left behind the cometary fragments. Kasaba et al.  reported the Jovian hectometric and kilometric radiation observed by GEOTAIL. They did not find clear enhancement in the whole period nor around each impact time. They suggested that there were few amounts of direct coupling between the cometary fragments and the Jovian outer magnetosphere. Further studies should be needed on dust-plasma interactions.
(Y. Kasaba: firstname.lastname@example.org)
The ray tracing is a very useful tool to study various wave phenomena in the magnetosphere and ionosphere, and has contributed to the exploration of magnetospheric plasma environments. Kimura  reviewed the ray tracing technique, to stress its significance in the history of the discovery of the magnetosphere.
The Akebono observation contributed to the modeling of the plasmaspheric plasma distribution. Using propagating wave characteristics obtained by the Akebono satellite and the ray tracing technique, Kimura et al.  developed the global model of the electron density distribution in the plasmasphere. The validity of the proposed model was checked and found that the model is flexible enough to represent the plasma distribution in the plasmasphere.
Propagation characteristics of mid-latitude whistlers are not still well understood which need further studies; for example, enhancement factor, duct dimension, interduct spacing, and duct terminating height. Ohta et al.  and Ohta et al.  reported characteristics of mid-latitude whistler ducts as deduced from ground-based measurements (Hobart, Australia, and Dunedin, New Zealand). Their study showed duct dimension, terminated altitude of ducts, life time of ducts and presence of a non-ducted PL whistler.
At planet Jupiter, whistlers are observed near the Io plasma torus. These whistlers are believed to be generated by lightning strokes. The estimation of whistler amplitude can derive the power of a lightning stroke. Hobara et al.  and Hobara and Hayakawa  analyzed the wideband wave-form data from Voyager 1, and reexamined the amplitude of many whistlers. The mean radiation power per flash of the lightning in the Jovian atmosphere was estimated to be order of hundred to ten million Watt.
(A. Morioka: email@example.com)
1) Remote sensing with plasma sounder technique:
The plasma sounder technique in Japan was established onboard the EXOS-B satellite (launched in 1978), and successfully applied to the topside sounding experiments onboard the EXOS-C (1984), and EXOS-D (1989) satellites, including the task to make an active experiment in space plasma. This instrument has been installed onboard the Planet-B satellite to realize the topside sounding of Martian ionosphere [Ono et al., 1998]. The plasma sounder instrument has been further developed to make an altimeter experiment onboard the Planet-B [Oya and Ono, 1998] which makes it possible to obtain the land shape of Mars as well as the total electron content (TEC) of Martian ionosphere by measuring the sounder RF echoes in HF frequency range. The possible applications of the Planet-B altimeter data and radar sounder experiment planed onboard the SELENE satellite have been studied from the viewpoint of the physics of solid planets and moon [Okada and Ono, 1998; Yamaji et al., 1998].
2) Passive plasma wave experiments and in-situ plasma measurement:
The instrumentation of the plasma wave experiment in VLF range had been established through the EXOS-D and Geotail satellites by using two sets of long deployed dipole antennas and three axes loop antennas [Hashimoto et al., 1997]. The VLF instrument was further developed for Planet-B mission facilitating DSP chip [Matsumoto et al., 1998b] to realize the small and right-weight electronics package onboard the Planet-B spacecraft. To evaluate the absolute intensity of the VLF plasma waves and to extend to examine the plasma parameters, the antenna impedance in VLF frequency range has been experimentally studied [Tsutsui et al., 1997] for the Geotail 50m wire-antenna element immersed in the magnetospheric and solar wind plasma. As an application of the full wave approach on VLF waves, a VLF wave technique was applied to measure the electron number density in the lower ionosphere [Okada, 1997]. The application of antenna impedance measurement in HF frequency range had already be established as Impedance Probe technique giving absolute number density of electrons in the ionosphere, plasmasphere and magnetosphere. Due to the compact shape and high reliability of the instrument, the impedance probe technique has been applied to wide research field in space such as the sporadic-E ionosphere dynamics [Yamamoto et al., 1998], and the dynamics and chemistry of neutral gases in the upper atmosphere of the polar region [Iwagami et al., 1998].
3) Data processing technique:
Two kinds of artificial neural network approaches have been developed to apply on the problems of ELF/VLF wave experiments in space. The one is to solve the problem in the direction finding analysis within a limited available data [Hirari and Hayakawa, 1996a, 1996b]. They demonstrate the validity of the artificial neural network approach by reconstructing wave distribution with two sources. The other approach [Yagitani et al., 1996b] is to realize the automatic classification of plasma wave waveform data onboard a spacecraft to minimize the necessary data transmission speed to the ground.
(T. Ono: firstname.lastname@example.org)
A. Wave emission
Hobara et al.  studied amplification of whistler waves by electron beams including the effect of inhomogeneity of the magnetic field. This problem is important to understand wave emissions in the magnetosphere, such as triggered ELF/VLF emission. Their result shows that the amplification through the flux tube has a quasi-periodic structure as a function of the wave frequency and electron beam velocity. This quasi-periodic structure oscillates from positive (grow) to negative (decay) when the electron beam is delta-function-like distribution in the velocity space, whereas it is always positive for the step-like distribution.
Another problem of wave generation has been attacked by Nunn et al.  using satellite observation and numerical simulation. Geotail satellite observed VLF chorus and discrete emissions in the band of 200-1200Hz around the equatorial region about L=10. The authors used a Vlasov code to simulate this emission, and the result is in good agreement with the observation. The simulation suggests that the underlying mechanism of the VLF chorus and emissions is the nonlinear trapping of cyclotron resonant electrons. (See also Section H1.4)
B. Ion-cyclotron instability
A series of particle simulations have revealed new aspects of current driven ion-cyclotron instabilities [Ishiguro et al., 1996a, 1997a, 1997b, 1998]. Ishiguro et al. [1997a] performed a two-and-half dimensional electrostatic magnetized simulations with electron beams. They found that ion-cyclotron instability creates different wave-front patterns depending on the spatial shape of the electron beam.
The ion-cyclotron instability is one of the promising candidates for the generating mechanism of the auroral potential drop (large potential drop along the magnetic field line). However, such a large potential drop was not found in this simulation because of the periodic boundary condition [Ishiguro et al., 1996a]. Ishiguro et al. [1997b] have constructed a simulation model with open boundary condition, and successfully produced a V-shaped dc potential structure, which has similar features to the auroral potential drop.
Another interesting related topic has been investigated by means of laboratory experiment: ion cyclotron instability due to ion beams. Mineo et al.  have carried out an experiment by modifying a Q-machine device, to excite electrostatic ion-cyclotron waves by an ion beam. The new finding of this experiment is that the waves are excited when the ion beam forms a self-organized spatial structure due to the magnetic focusing effect.
C. Kelvin-Helmholtz instability
MHD Kelvin-Helmholtz instability at the magnetopause plays an important role in the solar wind-magnetosphere coupling process. Miura  has examined the effect of the magnetic field orientation on the wave growth. Using two dimensional MHD simulation code, he concluded that the northward Bz in the magnetosheath is more favorable for the wave growth. This result can be important for the Bz control of the magnetospheric phenomena, for which the magnetic reconnection process has been predominantly investigated.
D. New analytical methods
Two new analytical technique for linear kinetic calculation have been developed by Nakamura , and Nakamura and Hoshino . One is for the field integration along the particle orbit . He obtained an alternative expression for this integration that allows drift approximation for the particle orbit. As an example of this method he solved the problem of lower hybrid drift instability in a curved magnetic field, to which the conventional method is not applicable.
The other method is for the integration of the distribution function over the velocity space . It approximates the distribution function with a one-over-polynomial function so that various analytical technique, such as the residue theorem, can be applied. This method can calculate to complicated resonance processes such as relativistic cyclotron resonance.
(T. Nakamura: email@example.com)
Recent discovery of the electrostatic solitary waves (ESW) in the earth's magnetotail by the Geotail spacecraft (references are found in Miyake et al. ) has motivated a number of theoretical and numerical efforts to explain the observed characteristics of the waves. Miyake et al.  perform two- dimensional full particle simulations of an electron beam system and find that the Bernstein-Greene-Kruskal (BGK) potentials, initially generated by the electron beam, subsequently coalesce each other and form potential troughs, almost uniformly in perpendicular directions to the background magnetic field. Structure of these quasi-one-dimensional BGK solutions are examined theoretically by Krasovsky et al.  using the Vlasov-Poisson equations. They discuss the dependence of the typical width of the solitary wave on its drift velocity and the wave amplitude.
Nonlinear wave-particle interactions are studied for a variety of applications. Summers et al.  discuss the flow of a neutralized electron beam in the Pierce beam-plasma system, by evaluating dynamics of Gelerkin truncated system. Interaction of charged particles with various types of one- dimensional pulses is studied by Akimoto , in which dependence of the interaction on pulse size, initial particle velocity, and external magnetic field are discussed. A new mechanism for Langmuir wave localization, due to trapping of beam particles, is proposed by Akimoto et al. . In a general setting, Krasovsky and Matsumoto  analyze the motion of electrons in gyroresonance with a general quasi- monochromatic electromagnetic wave, and obtain a set of approximate equations of motion by gyro-averaging.
Large amplitude MHD waves and shock waves are ample sources of nonlinear phenomena. Shimazu et al. [1996a] study structure of collisionless parallel shocks by performing full particle simulations, and find that the shock transition region is comprised of two physically distinct regions, and that the electromagnetic waves may play roles in the thermal diffusion of particles downstream. The study is extended to include heavy ions [Simazu et al., 1996b], in which they discuss roles of electromagnetic waves, the shock front re-formation, and thermalization of heavy ions. Recent advances in the physics of nonlinear waves in space plasmas (with emphasis on MHD waves) are documented in a monograph by Hada and Matsumoto , in which nonlinear evolution of quasi-parallel MHD waves is discussed in detail by Mjolhus and Hada , recent development of the theory of nonlinear plasma maser is thoroughly reviewed by Nambu and Vladimirov , and nonlinear ELF-VLF effects observed on ACTIVNY satellite are discussed by Molchanov et al. .
The nonlinear properties of the magnetic reconnection process have also been intensively studied during the period, presumably inspired by Geotail observations. Using three dimensional MHD simulation code, Ugai and Shimizu  show that, only when the central current sheet is sufficiently long in the direction of the current, the fast reconnection fully develops by the self-consistent coupling between the global reconnection flow and the current-driven anomalous resistivity. Numerical simulation studies of generation, propagation, and subsequent evolution of plasmoids are studied by Ugai  in 2-d, and by Ugai and Wang  in 3-d settings. Biscamp and Sato  analyze the effect of the electron pressure gradient in Ohm's law on the nonliner development of the internal kink mode, and discuss its relevance to the sawtooth phenomenon in tokamak plasmas. Kitabata et al. , by performing compressible MHD simulations in an open system, find that the energy release due to the driven magnetic reconnection is impulsive and intermittent, and that the reconnection rate is much enhanced during the impulsive phase.
The plasma, being far from thermal equilibrium in general, with inherent nonlinear couplings between internal modes, and with options of contacting external sources, provides an excellent medium for studying nonlinear dynamical properties of complex systems. Sato et al.  and Sato  emphasize the importance of three key elements in the self-organization process of a plasma, i.e., energy pumping, entropy expulsion, and nonlinearity, by presenting various numerical simulation results. The roles of thermal conduction is studied by Zhu et al. . Without the thermal conduction, an MHD system self- organizes itself to a non-Taylor state, but it shifts to a force-free minimum energy state under influence of the thermal conduction. Bazdenkov and Sato  study the reconnection in an isolated straight magnetic flux tube with all the field lines continuously twisted. Drastic topological changes and prominent burstlike thermal energy release are found to take place. The role of energy input in the formation of ordered structures in a semi-open system is examined by Yabuki et al. , by performing MHD simulations with a viscous membrane inside of the simulation system, which acts as a high-pass filter.
(T. Hada: firstname.lastname@example.org)
Setting up a field-aligned potential is a very efficient way of accelerating charged particles but the physics of its formation is still not uncovered yet. Ishiguro et al. [1995, 1996b] have reported on new two-dimensional electrostatic simulations of potential formation along converging field lines. While the results are quantitatively different from those in the previous works based on one-dimensional configuration, they are in good agreement with the Q-machine experiment results.
(M. Fujimoto: email@example.com)
Computer experiments are also performed to interpret the phenomena observed in active experiments. Ueda et al.  studied the excitation of upper hybrid waves associated with the ionospheric heating experiments. They focused on a direct conversion process which is proposed as an excitation mechanism of the upper hybrid waves where the energy of an obliquely propagating EM pump wave is converted into the ES upper hybrid waves due to small-scale density irregularities.
One of the significant applications of radio waves in space is the microwave energy transmission. Matsumoto  presented an excellent review paper on the microwave power transmission from space and the related nonlinear plasma effects. The paper covers not only a brief history of the development of technology and scientific research related to the transmission of electrical energy via radio waves, but also various kinds of experiments related the microwave energy transmission and associated theoretical and numerical studies. In the theoretical studies and numerical simulations [Matsumoto et al., 1995a, 1995b; Shinohara et al., 1996], the nonlinear interactions of intense microwaves with the ionospheric plasma, particularly, nonlinear wave-wave coupling and the resulting wave excitation at low frequency, are examined, which attempt to interpret the results obtained in a rocket-to-rocket power experiment called MINIX. From the technological point of view, microwave devices such as rectenna and cyclotron wave converter (CWC) have been studied in the association with the microwave energy transmission [Miura et al., 1997; Shinohara et al., 1998a, 1998b ; Vladimir et al., 1998a, 1998b].
(H. Usui: firstname.lastname@example.org)
In the field of computer experiments, Usui et al.  brought in an internal conducting body representing the spacecraft into the simulation region. To do this, they assume the spacecraft as a conducting body for simplicity. In the lecture of International School for Space Plasma Simulation, they described the numerical treatment of conducting spacecraft in terms of capacity matrix method. Some applications of this method in the study of the interaction between a spacecraft and space plasma were also introduced.
A 2-1/2 dimensional, full relativistic cylindrical particle simulation code was newly developed in both electrostatic and electromagnetic manners [Onishi et al., 1997]. This code adopts a fixed boundary for radial direction, and a periodic one for rotational direction. By using this simulation code, we will become able to perform computer experiments with cylindrical shape model such as magnetrons.
Realistic models of electromagnetic particle simulations require very large memory and very fast computing capability of supercomputers. Even a very powerful supercomputer with a shared memory may not be fast enough and not have very large memory. Therefore we are looking for a way to utilize parallel computers with distributed memories. Parallel computing is likely to be the most important new technology for space plasma simulations. There are three ways to adapt particle simulation code for parallel computers. The first one is to leave simulation code to parallel optimizations in each parallel computer. There is nothing for us to do in this case. The second one is to make a minor modification to the code using some special directives for parallel computers. The third choice is to change the code substantially for parallel computing environment realized by a software "PVM (Parallel Virtual Machine)". Ueda et al.  uses simulation code, KEMPO1, and modified the structure of the code so that it works efficiently on the parallel computing platform provided by PVM. Via PVM, we separated KEMPO1's simulation region and transported boundary data and superparticle data. This new code is flexible and scalable. The computation time is decreased in proportion to the number of separations, because each separated region is computed by an independent processor. On the other hand, the separation number is a bottleneck that limits the speed of transportation time. We must develop an efficient algorithm for data transportation.
Okada et al.  developed a new algorithm for the electromagnetic particle code using unstructured-cell as a grid model. In order to take into account more realistic shape of a spacecraft in the simulation space, a new discretization technique of Maxwell's equations was introduced to integrate Maxwell's equations in time and space. They show two kinds of algorithms to obtain the charge density and the current density. A two-dimensional unstructured-cell electromagnetic particle code has been implemented. They adopt triangular mesh as the electric and magnetic field grid and linear interpolation algorithm as the interpolation to the particle-pushing fields. One of the most advantages of this code would be for the modeling of the electromagnetic environment in the vicinity of a spacecraft.
(M. Okada: email@example.com)
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Okada, M. and H. Matsumoto , Electromagnetic particle simulation of spacecraft plasma environment with 2-D unstructured-cell Model, AGU
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Sato, T. and the Complexity Simulation Group , "Complexity in plasma: From self-organization to geodynamo," Phys. Plasmas, vol.3, 5, pp.2135-2142
Shibata, T., H. Kataoka and T. Okuzawa , "Ionospheric manifestation of Sc-associated magnetic pulsations in the HF Doppler frequency shifts," J. Geomag. Geoelectr., vol.49, pp.S179-S185
Shimazu, H., S. Machida and M. Tanaka [1996a], "Macroparticle simulation of collisionless parallel shocks generated by solar wind and planetary plasma interactions," J. Geophys. Res., vol.101, A4, pp.7647-7658
Shimazu, H., M. Tanaka and S. Machida [1996b], "Behavior of heavy ions in a collisionless parallel shock generated by the solar wind and planetary plasma interactions," J. Geophys. Res., vol.101, A12, pp.27565-27571
Shinohara, I., T. Nagai, M. Fujimoto, T. Terasawa, T. Mukai, K. Tsuruda and T. Yamamoto , "Low-frequency electromagnetic turbulence observed near the substorm onset site," J. Geophys. Res., vol.103, pp.20365-20388
Shinohara, K., K. Yumoto, A. Yoshikawa, O. Saka, S.I. Solovyev, E.F. Vershinin, N.B. Trivedi, J.M. Da Costa and the 210 deg. MM Magnetic Observation Group , "Wave characteristics of daytime and nighttime Pi 2 pulsations at the equatorial and low latitudes," Geophys. Res. Lett., vol.24, 18, pp.2279-2282
Shinohara, K., K. Yumoto, N. Hosen, A. Yoshikawa, H. Tachihara, O. Saka, T.-I. Kitamura, N.B. Trivedi, J.M. Da Costa and N.J. Schuch , "Wave characteristics of geomagnetic pulsations across the dip equator," J. Geophys. Res., vol.103, pp.11745-11754
Shinohara, N. and H. Matsumoto [1998a], " Experimental study of large rectenna array for microwave energy transmission," IEEE-MTT, vol.46, 3, pp.261-268
Shinohara, N. and H. Matsumoto [1998b], "Dependence of dc output of a rectenna array on the method of interconnection of its array element," Electrical Engineering in Japan, vol.125, 1, pp.9-17
Shinohara, N., D.R. Shklyar and H. Matsumoto , "Numerical analysis of self-focusing effect caused by inhomogeneity of microwave energy density in ionosphere," Electronics and Communications in Japan, Part1, vol.79, 9, pp.92-103
Shiokawa, K., K. Yumoto, Y. Tanaka, H. Osaki, M. Sato, T. Kato, Y. Kato, M. Sera, Y. Ikegami, S.-I. Akasofu, K. Hayashi, T. Oguti, and Y. Kiyama , "Auroral observations using automatic optical instruments: Relations with multiple Pi 2 magnetic pulsations," J. Geomag. Geoelectr., vol.48, pp.1407-1420
Shiokawa, K., W. Baumjohann, G. Haerendel, G. Paschmann, J.F. Fennell, E. Friis-Christensen, H. Luhr, G.D. Reeves, C.T. Russell, P.R. Sutcliffe and K. Takahashi , "High-speed ion flow, substorm current wedge, and multiple Pi 2 pulsations," J. Geophys. Res., vol.103, pp.4491-4507
Sibeck, D.G., K. Takahashi, K. Yumoto and G.D. Reeves , "Concerning the origin of signatures in dayside equatorial ground magnetograms," J. Geophys. Res., vol.103, pp.6763-6769
Summers, D., R. Thorne and H. Matsumoto , "Evaluation of the modified plasma dispersion function for half-integral indices," Phys. Plasmas, vol.3, 7, pp.2496-2501
Summers, D., H. Matsumoto and T. Ohnishi , "Spectral analysis of the flow of a neutralized electron beam," Intl. J. Bifurcation and Chaos, vol.7, 5, pp.1075-1101
Tachihara, H., M. Shinohara, M. Shimoizumi, O. Saka and T.-I. Kitamura , "Magnetometer system for studies of the equatorial electrojet and micropulsations in equatorial regions," J. Geomag. Geoelectr., vol.48, pp.1311-1319
Takeuchi, T., S. Iizuka and N. Sato , "Ion acoustic shocks formed in a collisionless plasma with negative ions," Phys. Rev. Lett., vol.80, pp.77-80
Takizawa, H., A. Morioka, H. Misawa and H. Miyaoka , "Periodic LF wave radiation associated with pulsating aurora," Proc. NIPR Sympo. on Upper Atmos. Phys., vol.11, pp.61-71
Tanaka, Y.-M., K. Yumoto, M. Shinohara, S.I. Solovyev, E.F. Vershinin, B.J. Fraser and D. Cole [1998a], "Coherent Pc 3 pulsations in the prenoon sector observed along the 210 deg. magnetic meridian," Geophys. Res. Lett., vol.25, 18, pp.3477-3480
Tanaka, Y.-M., K. Tang, K. Yumoto, N.B. Trivedi and T.-I. Kitamura [1998b], "Geomagnetic pulsations at the conjugate stations during the March 9, 1997, Total Solar Eclipse," Mem. Fac. Sci., Kyushu Univ., vol.30, 2, pp.81-89
Tsutsui, M., I. Nagano, H. Kojima, K. Hashimoto, H. Matsumoto, S. Yagitani and T. Okada , "Measurements and analysis of antenna impedance aboard the Geotail spacecraft," Radio Sci., vol.32, 3, pp.1101-1126
Ueda, H.O., Y. Omura and H. Matsumoto , "Computer simulations for direct conversion of the HF electromagnetic wave into the upper hybrid wave in ionospheric heating experiments," Ann. Geophysicae, 16, pp.1251-1258
Ueda, Y., Y. Omura and H. Usui , Electromagnetic particle simulations via parallel virtual machines, Proc. of The 5th International School/Symposium for Space Simulations, pp.399-402
Ugai, M. , "Computer studies on dynamics of a large-scale magnetic loop by the spontaneous fast reconnection model," Phys. Plasmas, vol.3, 11, pp.4172-4180
Ugai, M. and T. Shimizu , "Computer studies on the spontaneous fast reconnection mechanism in three dimensions," Phys. Plasmas, vol.3, 3, pp.853-862
Ugai, M. and W.B. Wang , "Computer simulations on three-dimensional plasmoid dynamics by the spontaneous fast reconnection model," J. Geophys. Res., vol.103, A3, pp.4573-4585
Usui, H.  Numerical treatment of conducting body in space plasma simulations, Proc. of The 5th International School/Symposium for Space Simulations, pp.206-208
Usui, H., J. Koizumi and H. Matsumoto , "Statistical study on electron cyclotron harmonic waves observed at the dayside magnetosphere," Adv. Space Res., vol.20, pp.857-860
Vanke, V.A., H. Matsumoto and N. Shinohara [1998a], "A new microwave input amplifier with high self-protection and rapid recovery," IEICE Trans. Electron, vol.E81-C, 5, pp.788-794
Vanke, V.A., H. Matsumoto, N. Shinohara and A. Kita [1998b], "Cyclotron wave converter of microwave into DC," IEICE Trans. Electron, vol.E81-C, 7, pp.1136-1142
Watanabe, T. H., T. Sato and T. Hayashi , "Magnetohydrodynamic simulation on co- and counter-helicity merging on spheromaks and driven magnetic reconnection," Phys. Plasmas, vol.4, pp.1297-1307
Wu, X.-Y., I. Nagano, Z.-T. Bao and T. Shinbo , "Numerical simulation of the penetration and reflection of a whistler beam incident on the lower ionosphere at very low latitude," J. Atmos. Terr. Phys., vol.58, 10, pp.1143-1159
Yabuki, K., K. Watanabe and T. Sato , "Roles of viscous membrane in an MHD self-organization," J. Phys. Soc. Jpn, vol.66, 7, pp.2026-2032
Yagitani, S., I. Nagano, H. Matsumoto, Y. Omura, W.R. Paterson, L.A. Frank, and R.R. Anderson [1996a], "Generation and propagation of chorus emissions observed by Geotail in the dayside outer magnetosphere," Proc. of 1996 International Symposium on Antennas and Propagation, vol.3, pp.717-720
Yagitani, S., T. Toda, I. Nagano, K. Hashimoto, T. Okada, H. Matsumoto and M. Tsutsui [1996b], "Neural network for plasma wave classification onboard satellite," Proc. of 1996 International Symposium on Antennas and Propagation, vol.3, pp.721-724.
Yamaji, A., S. Sasaki, Y. Yamaguchi, T. Ono, J. Haruyama and T. Okada , "Lunar tectonics and its implications for the origin and evolution of the Moon," Mem. Geolo. Soc. Japan, no.50, pp.213-226
Yamamoto, M., T. Ono, H. Oya, R. Tsunoda, M.F. Larsen, S. Fukao and M. Yamamoto , "Structures in sporadic-E observed with an impedance probe during the SEEK campaign: Comparisons with neutral-wind and radar-echo observations," Geophys. Res. Lett., vol.25, 11, pp.1781-1784
Yamashita, F., H. Usui and H. Matsumoto , "Computer experiments on the electromagnetic environment in the vicinity of a reentry vehicle," Proc. of The 5th International School/Symposium for Space Simulations, pp.404-406
Yoshikawa, A. and M. Itonaga , "Reflection of shear Alfven waves and the divergent Hall current," Geophys. Res. Lett., vol.23, pp.101-104
Yumoto, K. and the 210 deg. MM Magnetic Observation Group [1996a], "The STEP 210 deg. magnetic meridian network project," J. Geomag. Geoelectr., vol.48, pp.1297-1309
Yumoto, K., H. Matsuoka, H. Osaki, K. Shiokawa, Y. Tanaka, T.-I. Kitamura, H. Tachihara, M. Shinohara, S.I. Solovyev, G.A. Makarov, E.F. Vershinin, A.V. Buzevich, S.L. Manurung, Obay Sobari, Mamat Ruhimat, Sukamadradjat, R.J. Morris, B.J. Fraser, F.W. Menk, K.J.W. Lynn, D.G. Cole, J.A. Kennewell, J.V. Olson and S.-I. Akasofu, [1996b], "North/south asymmetry of sc/si magnetic variations observed along the 210deg. magnetic meridian," J. Geomag. Geoelectr., vol.48, pp.1333-1340
Yumoto, K., V. Pilipenko, E. Fedorov, N. Kurneva, M. De Lauretis and K. Kitamura , "Magnetospheric ULF phenomena stimulated by ssc," J. Geomag. Geoelectr., vol.49, pp.1179-1195
Yumoto, K., E.F. Vershinin, A.V. Buzevich, K. Saita and Y. Tanaka , "Relationships among seismic activity, atmospheric electric field, electromagnetic emissions and local magnetic activity in Kamchatka," Mem. Fac. Sci., Kyushu Univ., Ser. D, Earth Planet. Sci., vol.30, 1, pp.15-22
Zhang, Y. and H. Matsumoto , "Magnetic noise bursts near the interplanetary shock associated with the coronal mass ejection event on February 21, 1994: The Geotail observations," J. Geophys. Res., vol.103, pp.20561-20579
Zhang, Y., H. Matsumoto and H. Kojima [1998a], "Lion roars in the magnetosphere: The Geotail observations," J. Geophys. Res., vol.103, pp.4615-4626
Zhang, Y., H. Matsumoto and H. Kojima [1998b], "Bursts of whistler mode waves in the upstream of the bow shock: Geotail observations," J. Geophys. Res., vol.103, pp.20529-20540
Zhu, S.-P., R. Horiuchi and T. Sato , and the Complexity
Simulation Group, "Self-organization process of a magnetohydrodynamic
plasma in the presence of thermal conduction," Phys. Plasmas, vol.3, 7,