Investigating the development of double‐peak subauroral ion drift (DSAID)

Abstract

AbstractThis study focuses on the newly described ionospheric feature, called double‐peak subauroral ion drift (DSAID), which is a subclass of the well‐known single‐peak SAID. Double‐layer Region 2 (R2) field aligned currents (FACs) could be the main driver of DSAID. Our aim is to gain new insights into the development of DSAID during its two‐stage progression. Observational results are provided by five scenarios, each demonstrating a certain progression sequence of DSAID. Results show that SAID/DSAID occurred during flux transfer events and was accompanied by flow channels (FCs) associated with dayside magnetopause (FC‐2) and nightside magnetotail (FC‐3) reconnections, with westward electrojet (eastward FC), and with auroral streamers (FC‐4). In the premidnight magnetic local time (MLT) sector of stage 2, DSAID development was due to the short‐circuiting of the reconnection‐injected plasma jets during substorms or pseudobreakups. Thus, the related ring current pressure buildup enhanced the downward R2 FACs leading to double/multiple circuits forming double‐layer R2 FACs. During the midnight MLT hours of stage 2, DSAID development was closely related to the westward traveling surge (WTS)/substorm current wedge (SCW). WTS/SCW‐related strong upward R1 FACs closed with meriodional currents producing eastward and downward (i.e., downward R2 FAC‐style) return currents enhancing the downward R2 FACs and thus leading to double/multiple circuits forming double‐layer R2 FACs. Auroral streamers/FC‐4 represent a substorm substructure and their occurrence with DSAID after stage 2 demonstrates that this substructure occasionally includes DSAID. Our results demonstrate also that the short‐circuited system underlying SAID/DSAID acted sometimes as a current generator and sometimes as a voltage generator.