The Low Energy Neutral Atom (LENA) imager on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft in the magnetosphere can detect neutral particles coming from the direction of the magnetopause. During a period of dynamic pressure of 0 nPa and IMF BZ of +/ nT on March ,1, ,**+, significant neutral atom emissions occurred in the direction of the very high-latitude magnetopause. Simultaneous observations from IMAGE/LENA and SuperDARN radar show that the LENA emission appears concurrently with the enhancement of the sunward flow of the reverse convection in the ionosphere. In a recent paper (S. Taguchi et al., Geophys. Res. Lett., --, L*-+*+, doi: +*.+*,3/,**/GL*,/*,*, ,**0) this type of emission has been interpreted as being produced by the fast ion flow caused by cusp reconnection through charge exchange with the Earth’s hydrogen exosphere. In other words, remote sensing using LENA imager can be applied in order to determine the stability of the reconnection site. From results of analyses of LENA emission data we show that the reconnection “spot” mapped on a sphere having a radius of 2 RE shifts tailward by approximately + RE over +*min while fluctuating. key words: cusp, neutral atoms, reconnection, IMF
In this report, we examined diamagnetic and anti-diamagnetic (paramagnetic) properties of magnetosonic modes in anisotropic fluid pressure condition by incorporating double adiabatic equations of state. In the context of liner perturbations, it is found that there appear two wave modes corresponding to a slow phase velocity and a fast phase velocity as is resembled to those in isotropic plasmas. For the fast phase velocity mode, pressure perturbations and field perturbations exhibited paramagnetic relations, similarly to isotropic plasmas. For the slow phase velocity mode, paramagnetic properties appear, unlike the isotropic case, at higher plasma beta part of lower pressure anisotropy (perpendicular/parallel) region. key words: anisotropic plasmas, magnetosonic waves, diamagnetic and anti-diamagnetic properties
Solar zenith angle and solar activity dependences of electron number density distribution in the nightside auroral region from the topside ionosphere to the magnetosphere within a geocentric radial distance of 2.6 RE were statistically investigated based on 7-years plasma wave data obtained by the Akebono (EXOS-D) satellite. Electron number density Ne is derived from the upper limit frequency of whistler-mode auroral hiss, which is almost equal to plasma frequency fpe in the polar region. In order to focus on the nightside auroral region, the datasets obtained in a sector from 2100 to 0300 MLT were selected for the analyses in this study. In order to investigate seasonal and solar activity dependence of electron number density, the selected datasets were divided into 12 sub-datasets depending on solar zenith angle (SZA) and phase of the solar cycle. In this study, the periods from April, 1989 to March, 1992, and from July, 1993 to June, 1997 are defined as solar maximum, solar minimum, respectively. For each sub-dataset, the average electron number density in each spatial bin with 500 km square in the meridian plane. The results are summarized as follows: (1) Electron number density Ne changes depending on SZA and solar activity: Ne in sunlight is about 3 times larger than that in darkness, and Ne during solar maximum is about 10 times larger than that during solar minimum. (2) The polar low density region with an Ne range below 100/cc during solar maximum is wider than that during solar minimum. The plasmapause is at L=3.5 during solar maximum while it becomes at L=4.5 during solar minimum. (3) Vertical Ne profile varies depending on SZA and solar activity. The low density region with an Ne range below 100/cc
In order to study the ability of meteor burst communications (MBC) as a new medium of data collection networks in Antarctica, we have performed a series of VHF data transmission experiments. In the experiment during the period of JARE-43 (the 43rd Japanese Antarctic Research Expedition), a remote station at Zhongshan Station sent data packets to a master station at Syowa Station using a commercial MBC system. Together with meteor burst propagations, non-meteoric propagations were frequently observed during local nighttime. We found that they worked effectively for packet transmissions and greatly increased the data throughput. Overall data throughput obtained by this experiment was 0.63 bps. In JARE-44, we added another remote station at Dome Fuji Station. Since the transmitted power from the master unit was split into two directions, data throughput from Zhongshan Station was reduced to 0.36bps. That from Dome Fuji Station was only 0.13bps. For the experiment in JARE-45, we replaced the commercial MBC system with a RANDOM (RAdio Network for Data Over Meteor) system developed by the authors. The experiment is being conducted between Syowa and Zhongshan Stations. The estimated data throughput during the period from April 1st, 2004 to August 31st, 2004 was 2.9 bps.
Seasonal and solar cycle dependences of the correlation between auroral kilometric radiation (AKR) and the auroral electrojet (AE) index have been investigated based on the plasma wave data obtained by the Akebono satellite. Under any seasonal and solar activity conditions, a clear correlation has been found between the AKR power flux and the AE index. The properties of the correlation, however, vary depending on season and solar activity. AKR power flux increases as about the +., power of AE index in all seasonal and solar activity conditions. However, even for the same AE index, AKR power flux during solar minimum is / dB larger than that during solar maximum. As for the seasonal variations, the AKR power flux in winter is ,, dB larger than that in summer even for the same AE index. The results suggest that long-term variations of AKR depend not only on auroral current variations but also on factors associated with the total energy flux of auroral electrons and the generation process of AKR. key words: auroral kilometric radiation, AE index, seasonal dependence, solar cycle dependence, AKR index
We first present the results of simultaneous monitoring of subionospheric LF propagation over two di#erent paths prior to a very strong Tokachi-oki earthquake (near the east coast of Hokkaido Island on September ,/, ,**-) with magnitude 2.-. Nighttime amplitude fluctuations of the Japanese Time Standard Transmitter (JJY, .* kHz) signal received at Moshiri (Japan, geographic coordinates .. N, +., E) and at Petropavlovsk-Kamchatski, Russia (/N, +/2 E) were analyzed. As a possible precursory signature we observed synchronous intensification of quasi-periodic +0-day variations of the dispersion in the signals received at both observation stations before the earthquake. The strongest deviations observed as a rule were depletions of signal amplitude probably connected with an increase in loss in the ionosphere by the enhancement of turbulence. This is due to dissipation of internal gravity waves (IGW) at the lower ionospheric heights. A scenario of interconnection between seismo-activity, atmospheric gravity waves and planetary waves, is proposed to explain the observed association with strong earthquakes. key words: subionospheric LF propagation, earthquakes, ionospheric perturbations
HF ray path calculation is performed in order to identify possible ionospheric backscatter echo area for an HF radar at mid-latitude. The calculation is made on the basis of the R.M. Jones and J. J. Stephenson (U.S. Dept. of Commerce, OT Rep. 1/ 10, +31/) HF ray path tracing algorithm plus the IRI-,**+ ionosphere model. It is shown that depending on the local time and geomagnetic activity, the possible ionospheric backscatter regions have di#erent distributions. In any case the backscatter region is large enough, indicating the capability of a planned HF radar in Hokkaido (.-./ N, +.-.0 E), Japan. key words: ionospheric echoes, SuperDARN, mid-latitude, ray-path tracing
The inner magnetosphere occupies a vast volume in space containing a relatively low-density mixture of hot and cold plasmas: the ring current, plasmasphere and radiation belt. Energy is transferred from the ring current to the cold plasmas through Coulomb collisions and wave-particle interactions, producing temperature enhancements in the plasmasphere. The plasma waves generated in the plasmasphere cause pitch-angle and energy di#usion of the energetic particles. The magnetic disturbances generated from the ring current alter the drift paths of radiation belt particles, causing radiation belt flux dropout during magnetic storm main phases. The ionosphere is filled with dense and cold plasmas in a +***-km-thick shell above the Earth's surface at +** km altitude. Despite the distinct di#erences in size, location and physical properties, the ionosphere and the inner magnetosphere are tightly connected to each other. The ionosphere is an important source of magnetospheric ions. Energy transported down from the inner magnetosphere to the ionosphere produces observable temperature enhancements and optical emissions in the iono- sphere. The electric coupling between the ionosphere and magnetosphere explains features such as shielding field, non-linear response of the ring current to the plasma- sheet source, and the post-midnight enhancement of the storm-time ring current flux. Even though many signatures are well described from the perspective of magneto- sphere-ionosphere coupling, there are still unanswered questions, for example, the precise roles of wave-particle interactions in ring current loss and plasmaspheric heating, the cause of rapid storm initial recovery, the source of O enhancement at substorm expansion, and the causes of outer radiation belt enhancement during storm recovery. The unresolved questions can be answered through careful cross analysis of the observational data from the ongoing and future imaging and multi-point missions with simulation results of large-scale modeling.
This report presents Monte Carlo simulations of the electron energy distribu- tion for a low ionized plasma interacting with the F-region neutral gas. The results show a depletion in the electron distribution above 2 eV between 10 and 80%, decreasing with altitude. The depletion is mainly due to electron energy loss to N2. This micro-physical energy transfer model gives good agreement with optical observations of enhanced emis- sions from O( 1 D )a t 6300A and EISCAT UHF measurements of electron cooling during HF radio wave heating experiments. Some implications for incoherent scatter spectra are derived. The results suggest that a weak (approximately 1000 times weaker than the ion- line) and wide (2 MHz) peak around ±1 MHz from the ion-line in the EISCAT VHF inco- herent scatter spectrum should be a consequence of the electron-neutral interaction.
