Abnormal Sub‐Auroral Ion Drifts (ASAID) Developed in the Postmidnight (1–4) Magnetic Local Time Sector in 2013

Abstract

AbstractWe investigate the Abnormal Sub‐Auroral Ion Drifts (ASAID) developed in the postmidnight (1–4) magnetic local time sector in 2013. Shown by the Defense Meteorological Satellite Program F15 horizontal ion velocity measurements, we specified 21 antisunward (eastward) ASAID flow channels (FCs) based on their respective underlying polar convections. Overall, the polar convection formed a two‐cell pattern with its convection axis tilted in the morning‐evening direction because of the underlying BY < 0 conditions. Its dawn cell intruded into the duskside from the dawnside where the eastward ASAID flows were streaming antisunward, opposite to the dawn cell sunward convection flows. Mostly, the ASAID FC appeared in the coinciding ring‐current–related ionospheric trough and flow‐stagnation–related main ionospheric trough in the South American sector because of the favorable conditions created by the South Atlantic Magnetic Anomaly promoting also the development of Stable Auroral Red (SAR) arc. Rarely observed, the ASAID FC was associated with the SAR arc detected over Rothera. Detected in the Mid Pacific longitude sector, a pair of northern‐southern ASAID FCs demonstrated northern‐southern conjugacy. With correlated observations, demonstrating magnetosphere‐ionosphere conjugacy, the inward (earthward) ASAID electric (E) field could also be investigated. These reveal the ASAID E field's fast‐time development by short‐circuiting when the hot‐ring‐current—cold‐plasmasphere interface developed and became impacted by finite Larmor radius effects because of the earthward intrusion of hot ring current protons. The ASAID E field's inner‐magnetosphere environment was characterized by the hot zone where heating was generated by low‐frequency waves and auroral kilometric radiations.