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We developed a computer simulation scheme for the motion of energetic particles trapped in the Earth's magnetic field during a magnetic storm. The particles are injected into the inner magnetosphere from the near-Earth plasma sheet by a strong inductive electric field due to a dipolarization in association with a substorm. The motion of the particles is traced by the bounce-average approximation under a dipolar magnetic field and the Volland-Stern type convection field. The absolute quantity of a directional differential flux of the particles can be obtained. We can calculate the azimuthal component of the current density and an H-component of the magnetic disturbance at the center of the Earth (Dst^*) induced by the current. In this paper, we examine the formation of the ring current and the magnetic disturbance on the moderate storm occurred on February 13-14,1972. We find that (1) the inductive electric field due to the dipolarization may be one of major contributors to Dst^* on this storm, (2) the steep variations of Dst^* in the main phase cannot reproduced by the inductive electric field model, (3) the intensity of Dst^* is sensitive to the number density in the near-Earth plasma sheet, that is, an enhancement of the number density in the near-Earth plasma sheet may produce the steep and the major variations of Dst^*.

Auroral tomography is a state-of-the-art method to retrieve three dimensional (3D) structure of luminous aurora from images taken simultaneously at multiple observation points. Imaging is basically monochromatic and altitude structures as well as horizontal vortex structures at particular wavelength are reconstructed. These are crucial for quantitative understanding of auroral formation and dynamical processes. In March 1995,the first multi-point international campaign between Sweden and Japan was carried out using three unmanned Swedish ALIS stations (Kiruna, Merasjarvi, Tjautjas) and two Japanese sites (Abisko, Nikkaluokta), separated by about 50km in Kiruna region. ALIS stands for the Auroral Large Imaging System which aims at capturing large-scale composite auroral images as well as optical tomographic imaging by a computer-controlled networking. In this paper, a description is given on the analysis of auroral tomography on the reconstruction of folded auroral arc observed at 2340 : 30 UT on March 26,1995. The images are taken for 1-5s integration at a green line of 557.7nm. Cameras were pointed to one of the preset common field of view, viz., a core region which is just overhead of Kiruna. Optical tomography relying on inversion analysis by the algebraic reconstruction technique has been carried out. The result indicates a fold structure of auroral arc with inferred altitude profile of photo-emission peaking at around 120km.

The Monte Carlo method was applied to investigate electron auroras observed by the sounding rocket S-310JA-8,which was launched on April 4,1984 from Syowa Station in Antarctica of the invariant latitude 66.14°S and the geomagnetic longitude 70.98°. The number density of the atmosphere, in which constituent elements were assumed to be N_2,O and O_2,and temperatures were estimated by the MSIS-86 model for the aurora observed there. A downward electron differential number flux was measured at the altitude of 200km, from which electrons were injected downward into the upper atmosphere. An initial electron energy E_0 is investigated in the range from 100 eV to 18 keV. An initial pitch angle was assumed to be uniformly distributed in the range of [0,π/2].Ionization rates of N_2,O and O_2 were calculated as a function of an altitude, the initial pitch angle, and the initial electron energy. The total ionization rate obtained by summing up individual ionization rate was considered to be a production rate of thermal electrons. A loss rate of thermal electrons was estimated by using an electron density and an effective recombination rate. Under the assumption of local equilibrium of ionization and recombination, the height profile of electron density was deduced and compared with the observed one. The height profile of an emission rate was also investigated for the oxygen green line. The emission rate calculated as contribution from the electron impact was compared with the one produced by the collision process N_2 (A^3Σ_u^+)+O(^3P), and it was made clear that the latter collision process was more efficient to excite oxygen atoms from O(^3P) to O(^1S) than the electron impact in the wide range of electron energy observed by the sounding rocket.

Electron auroras observed by the sounding rocket S-310JA-8 are investigated by using the Monte Carlo method. The MSIS-86 model is employed to represent the atmospheric number density and temperature in the aurora observed at Syowa Station in Antarctica of the invariant latitude 66.14°S and the geomagnetic longitude 70.98°on April 4,1984. Only N_2,O and O_2 are taken into account as components of the atmosphere. Electrons are injected downward into the upper atmosphere at the altitude of 200km, at which a downward electron differential number flux was measured. An initial electron energy E_0 is considered in the range of 100eV to 18keV. It is assumed that an initial pitch angle is uniformly distributed in the range of [0,π/2]. Production and emission at λ427.8nm rates of the first negative band system of nitrogen molecular ions N^+_2 (B^2Σ^+_u) are calculated as a function of altitude, the initial pitch angle, and the initial electron energy. Time variation of the observed absolute intensity of this line is reasonably well reproduced by the Monte Carlo method combined with the measured electron number flux. The difference in the absolute intensities obtained by experiment and theory is 5% at the time X+216s. This confirms that the Monte Carlo method is applicable to simulate collision processes and the resulting production and emission rates in electron auroras. Some representative results of emission rates are also presented for oxygen green and red lines.

Development of the ring current is one of major phenomena during a magnetic storm in the Earth's magnetosphere. Ring current protons collide with other particles (e.g., geocoronal hydrogen and plasmaspheric electrons) and lose their energies within a few days. The primary loss processes for ring current protons are considered as; (i) charge exchange with the geocoronal neutral hydrogen, and (ii) Coulomb collision with the plasmaspheric thermal electrons. In order to estimate the loss rate caused by both loss processes numerically, it is essential to trace each particle along their trajectories because the drift paths basically depend on energy, pitch angle, initial position of charged particles and the magnetospheric electric and magnetic fields. For this purpose, we have developed a particle simulation code including the charge exchange and the Coulomb collision as the major loss processes with a time-dependent magnetospheric electric field. A new plasmaspheric density model is also developed to evaluate the Coulomb collision between the ring current protons and the plasmaspheric thermal electrons. This model is a two dimensional and time-development on plasmaspheric number density, derived from a continuity equation along a magnetic flux tube connecting with the conjugate ionospheres in both hemispheres. Using this model, we obtained the electron density distribution in the plasmasphere which was fairly consistent with the one obtained by EXOS-B satellite observation. In this paper, we demonstrate the trajectory of 100 eV (lower energy) and 100keV (higher energy) protons associated with a magnetic storm. Their energies are lost effectively by Coulomb collisions more than charge exchange loss process, and hence, thermal electron distribution in the inner plasmasphere gives an important effect for lower and/or higher energy protons.

Image Database Systems usually have some keywords selected by human decision. In recent years, it has been an interesting problem to develop a method by which shapes, colors and contents for a specific image from image files are recognized automatically through image processing. Furthermore, it becomes important to determine properly the keywords representing impression of images, that is, 'KANSEI' words. We try to construct a database and data search system of the DMSP satellite auroral image files. At first, an index file including information such as file name, size, date and geometric feature of images is created through image processing. The impressional items for auroral shapes such as brightness, position, and impression are derived by a coordinate conversion method so called the 'KANSEI' space method. The system contains about 100 image files and the index file. A specific image data is searched with the index file and the conversion method of 'KANSEI' words.

Energetic protons in the radiation belt of the earth's magnetosphere show energy density enhancement associated with geomagnetic storms/substorms, which observation with Explorer 45 evidently revealed as a nose structure in the E-t spectrogram inside the plasmasphere. An attempt has been made to explain this by an injection model in which energetic protons are injected around a nightside geosynchronous orbit with their subsequent inward motions due to a convection electric field possibly driven by the solar wind and a corotation electric field. It is also important to include a loss mechanism in the model inside the plasmasphere since the protons decay due to charge exchange loss processes with geocoronal neutral hydrogen. The loss rate of protons depends on the hydrogen density and charge exchange cross section. In this study, the effect of the charge exchange loss is examined by computer simulation of energetic proton trajectories in the magnetosphere; the hydrogen density being obtained by the Chamberlain model and the charge exchange cross section being adopted from the latest approximate formula. It is concluded that loss processes play an essential role in the energy density distributions of protons in the near earth radiation belts, especially inside L of about 4.

Aurora stereoscopic observation for the monochromatic regime has been carried out in Iceland in November and December, 1991. A distance between two observation sites, Husafell and Efri-Brunna, is about 90km in the magnetic meridian plane. The aim is to obtain stereo image data with longer baseline for the detailed study of inverse algorithm and to clarify three-dimensional luminous structures of aurora at typical wavelengths. This paper gives a brief description of the observation and some provisional results of data analysis.

An instrument has been developed for observing the high frequency modulations or fluctuations (upto several megahertzs) of the auroral electron flux. The instrument utilizes an on-board processing hardware for calculating autocorrelation functions of particle flux measured by any type of particle detector which output a series of pulses. Two rocket observations by using the instrument were carried out as a part of low energy auroral electron experiments on board the S-310JA-11 and -12 rockets which were launched into the Antarctic auroral ionosphere. The instrument is capable of measuring the flux modulations in three frequency ranges, i. e. 1.5-100Hz, 0.1-8kHz and 0.1-4MHz, respectively. Results from one rocket experiment launched under relatively quiet conditions indicate that the auroral electrons are almost uniform in the high frequency range. Results from another rocket experiment (JA-12) conducted under highly active aurora conditions show low frequency modulations of electron flux associated with a strong electron precipitation.

This report presents the spatial distributions of auroral X-rays obtained by the balloon flight named AZCO-C1,which was launched from Norway in July 1985. A time sequence of auroral X-ray images were derived by using a set of three NaI (T1) scintillation counters for each of the three different energy channels : 22-35,35-55 and 55-88keV. The precipitation region of energetic particles and its modulations with time were well demonstrated, though the X-ray enhancements were only three times the background flux.