[1] We studied magnetic field dipolarization and associated ion acceleration in the deep inner magnetosphere, using magnetic field data obtained by the magnetometer on board the Mission Demonstration Satellite 1 (MDS-1) and the energetic neutral atom (ENA) flux data obtained by the high-energy neutral analyzer imager on board the Imager for Magnetopause-to-Aurora Global Exploration satellite. Because the MDS-1 satellite has a geosynchronous transfer orbit, we could survey magnetic field variations at L = 3.0-6.5. Analyzing data in the period from February to July 2002, we found that (1) dipolarization can be detected over a wide range of L (i.e., L = 3.5-6.5, which is far inside the geosynchronous altitude); (2) when the MDS-1 satellite was located close to auroral breakup longitude, the occurrence probability of dipolarization was about 50% just inside the geosynchronous altitude and about 16% at L = 3.5-5.0, suggesting that dipolarization in the deep inner magnetosphere is not unusual; (3) magnetic storms were developing whenever dipolarization was found at L = 3.5-5.0; (4) dipolarization was accompanied by magnetic field fluctuations having a characteristic timescale of 3-5 s, which is comparable to the local gyroperiod of O + ions; and (5) after dipolarization, the oxygen ENA flux in the nightside ring current region was predominantly enhanced by a factor of 2-5 and stayed at an enhanced level for more than 1 h, while clear enhancement was scarcely seen in the hydrogen ENA flux. From these results, we conjectured a scenario for the generation of an O + -rich ring current, in which preexisting thermal O + ions in the outer plasmasphere (i.e., an oxygen torus known from satellite observations) experience local and nonadiabatic acceleration by magnetic field fluctuations that accompany dipolarization in the deep inner magnetosphere (L = 3.5-5.0).Citation: Nosé, M., H. Koshiishi, H. Matsumoto, P. C:son Brandt, K. Keika, K. Koga, T. Goka, and T. Obara (2010), Magnetic field dipolarization in the deep inner magnetosphere and its role in development of O + -rich ring current,
Département Environnement Spatial, Office National d'Etudes et de Recherches Aérospatiales (ONERA) has been developing a model for the geostationary electron environment since 2003. Until now, this model was called Particle ONERA‐LANL Environment (POLE), and it is valid from 30 keV up to 5.2 MeV. POLE is based on the full complement of Los Alamos National Laboratory geostationary satellites, covers the period 1976–2005, and takes into account the solar cycle variation. Over the period 1976 to present, four different detectors were flown: charged particle analyzer (CPA), synchronous orbit particle analyzer (SOPA), energetic spectra for particles (ESP), and magnetospheric plasma analyzer (MPA). Only the first three were used to develop the POLE model. Here we extend the energy coverage of the model to low energies using MPA measurements. We further include the data from the Japanese geostationary spacecraft, Data Relay Test Satellite (DRTS). These data are now combined into an extended geostationary electron model which we call IGE‐2006.
[1] We investigated a Pi2 pulsation that occurred at 0538 UT on 20 September 1995, using data from ground stations and the ETS-VI and EXOS-D satellites. Since ground stations at L = 1.45 À 12.6 and the two satellites were located at 7-10 hours of magnetic local time (MLT), we could investigate characteristics of the morning side Pi2 pulsation in detail. We also examined geomagnetic field data from equatorial and low-latitude (L 1.5) stations at 0200 MLT and 1500 MLT. Our findings include the following: (1) Pi2 pulsations on the morning side were observed over a wide range of L (L < 6.1) with almost identical period (T $ 70 s) and waveforms; (2) the ETS-VI satellite located above the geomagnetic equator at L = 6.3 observed a Pi2 pulsation that had nearly the same period and waveforms as the ground Pi2 pulsation; (3) the Pi2 pulsation observed by ETS-VI appeared in the compressional and radial components; (4) phase lag between the compressional and radial components was $180°(5) the ground-to-satellite phase lag was $180°($0°) for the X component and the compressional (radial) component; (6) the EXOS-D observation placed the plasmapause location at L = 6.8, across which ground Pi2 pulsations changed their characteristics; and (7) no phase delay was found between low-latitude Pi2 pulsations observed around 0700 MLT, 0200 MLT, and 1500 MLT. From these results we concluded that the morning side Pi2 pulsation was caused by the plasmaspheric cavity mode resonance and that its longitudinal structure was rather uniform.
The magnetic field data from the Engineering Test Satellite -VI (ETS-VI) have been analyzed to investigate the occurrence distributions of pulsations in Pc 3-5 frequency ranges in the magnetosphere. The observation of ETS-VI covered the invariant latitude (ILAT) range of 64.5• -69• ILAT near the geomagnetic equator (−10• -20• magnetic latitude) at all magnetic local time (MLT). Magnetic pulsations were selected by the Fast Fourier Transform method and checked by visual scanning if they have continuous waveforms. From the occurrence distributions of pulsations, we have found distinctive features in the following pulsations: (1) azimuthal Pc 5 pulsation; (2) azimuthal Pc 3 pulsation; (3) radial Pc 4 pulsation on the dayside; (4) azimuthal Pc 4 pulsations on the nightside. In respect of the first three types of pulsations (i.e., the azimuthal Pc 5 pulsation, the azimuthal Pc 3 pulsation, and the radial Pc 4 pulsation on the dayside), the results presented in this study confirm the previous results obtained by other satellite observations. The azimuthal Pc 4 pulsations on the nightside were observed in continuous waveforms lasting for about 10 minutes. Although the azimuthal Pc 4 pulsations on the nightside start at almost the same time as substorm onsets, they are different from Pi 2 pulsations in the magnetosphere. They are observed frequently in the MLT range of 23-04MLT with an occurrence peak at 01-02MLT. We suggest that the azimuthal Pc 4 pulsations on the nightside are excited through coupling to the fast mode Alfvén waves which were launched at substorm onset.
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