Simultaneous Observations of Poleward‐Moving Auroral Forms at the Equatorward and Poleward Boundaries of the Auroral Oval in Antarctica

Abstract

AbstractPoleward‐moving auroral form (PMAF) is a type of dayside auroral pattern. The distinguishing characteristic of a PMAF is its separation from the auroral oval and subsequent poleward motion. It has been reported and widely accepted that PMAFs occur more frequently during periods with dominant southward interplanetary magnetic field (IMF). However, most ground‐based optical observations were made near magnetic latitudes of 75°, close to the equatorward boundary of the dayside auroral oval; therefore, PMAFs occurring at the poleward boundary were likely missed easily. Using all‐sky images from two stations located on the similar magnetic meridian in Antarctica at 80° and 75° magnetic latitude, and taking solar wind data close to the magnetosphere by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft, we demonstrate that unlike the result from prior low‐latitude single‐station observations, the combined observations from both stations show an insignificant difference in the PMAF occurrence rate in the northward and southward IMF conditions and no clear sign suggesting that the southward IMF or southward turning of the IMF triggers PMAFs. With good agreements between PMAF occurrence rate and the intensity of the poleward drift, we suggest that PMAFs are more likely to be plasma patches torn away from the dayside auroral oval convecting antisunward and rather than direct foot points of reconnecting flux tubes.