Investigating the Development of Abnormal Subauroral Ion Drift (ASAID) and Abnormal Subauroral Polarization Stream (ASAPS) During the Magnetically Active Times of September 2003

Abstract

AbstractThis study investigates two recently reported subauroral phenomena: the abnormal subauroral ion drift (ASAID) appearing as an inverted SAID and the shielding‐E—SAID structure depicting a SAID feature on the poleward side of a small eastward or antisunward flow channel that is the shielding electric (E) field's signature. We have analyzed polar cross sections, constructed with multi‐instrument Defense Meteorological Satellite Program data, for the development of these subauroral phenomena. New results show the features of abnormal subauroral polarization stream (ASAPS) and ASAID‐ASAPS comprised by a narrow ASAID embedded in a wider ASAPS. We have identified undershielding, perfect shielding, and overshielding events. Our observational results demonstrate SAPS development during undershielding, the absence of subauroral flow channel during perfect shielding, and ASAID/ASAPS and shielding‐E—SAID/SAPS development during overshielding. The appearance of an ASAID‐ASAPS structure together with a pair of dayside‐nightside eastward auroral flow channels implies the intensification of region 2 field‐aligned currents via the westward traveling surge and thus the strengthening of overshielding conditions. From the observational results presented we conclude for the magnetically active time period studied that (i) the shielding E field drove the wider ASAPS flow channel, (ii) the ASAID‐ASAPS structure's narrow antisunward flow channel developed due to the injections of hot ring current ions in a short‐circuited system wherein the hot ring current plasma was closer to the Earth than the cold plasmaspheric plasma, and (iii) overshielding created this hot‐cold plasma configuration via the development of a plasmaspheric shoulder.