Paper#: 101
Poster #: 17
Session Name: Poster Session 2
Room: East Ballroom
Day: Thursday
Time: 10:10 a.m.-Noon
Abstract Title: Flux Enhancement of Energetic Particles in the Near-Earth Plasma Sheet: GEOTAIL-HEP Observation
PresentSurname: Hori, T.
All Authors: T. Hori, K. Maezawa, Y. Saito, T. Mukai, T. Takashima
Abstract : We have found that both the energy-dispersed and the dispersionless flux enhancements of energetic (>40 keV) particles are frequently observed far away (R>9 Re) from the Earth, which are similar to the ones observed at the geosynchronous orbit in association with substorms. Using energetic particle data obtained by the HEP-LD instrument onboard the GEOTAIL spacecraft, we studied spatial and temporal characteristics of these flux enhancement events and also examined their correlation with substorm activities. It was found that the dispersed events of energetic ions are distributed preferentially on the dusk side, while most of the dispersed electron events are found on the dawn side. On the other hand, the dispersionless events can be found only on the night side and are mostly distributed within R < 15 Re from the Earth. We also examined their correlation with substorm activities and found that almost all (96%) of the dispersionless and dispersed events are associated with substorms. The dispersionless flux enhancements in the plasma sheet proper occur within +/- 2 minutes of the corresponding substorm onset determined by Pi2 pulsation activities on ground magnetograms. Therefore, it is interpreted that energetic particles forming such flux enhancements are generated on the night side, and then drift azimuthally westward or eastward, to reach the other local time sectors. It was also found that some of the dispersed events have a long (~ several ten minutes) energy dispersion, indicating a possibility that energetic particles can occasionally complete a closed drift path around the Earth with radial distances of > 10 Re on the nightside.