Paper#: 7
Poster #: 9
Session Name: Poster Session 1
Room: East Ballroom
Day: Tuesday
Time: 10:10 a.m.-Noon
Abstract Title: Stepwise Evolution of Auroral Substorm Observed by Meridian Scanning Photometers at Syowa And Asuka Stations
PresentSurname: Kadokura, A.
All Authors: A. Kadokura, A.-S. Yukimatu, M. Ejiri
Abstract : We have analyzed auroral poleward expansion events observed by the meridian scanning photometers at Syowa and Asuka stations in Antarctica in 1989, and found that some type of the poleward expansion proceeded in a stepwise way. The first Stage-1 was characterized by a rapid poleward expansion both of the electron and proton main auroral ovals. During the next Stage-2, poleward expansion was very slowed and an intense discrete electron auroral activity appeared around the poleward edge of the main oval. During the Stage-3, a further poleward expansion re-started. Such a 3-stage evolution was observed in 22 of the total 88 events in 1989. Average duration of the Stage-1 and Stage-2 is 3.5 min and 12.5 min, respectively, and average start location of the initial poleward expansion is 62.7 deg. invariant latitude and 0.3 hr MLT. In 14 of the 22 events, a characteristic auroral activity, called as NPSBL (Near PSBL) aurora, was seen around the poleward edge of the entire auroral region before the Stage-1. In such a case, initial poleward expansion started at lower latitudes, and approached to the NPSBL aurora. Further poleward expansion during the Stage-3 started with a significant intensification of the NPSBL aurora. During the Stage-3, electron emission was bifurcated into two parts; poleward expanding and equatorward moving parts. Proton emission co-existed within the main oval during the Stage-1 to Stage-2, and became weak soon after the bifurcation. Such a weakening of the proton emission was observed in 13 of the 22 events.