Northeastward-Moving Auroral Forms From Possible High-Latitude Reconnection

摘要

This study presents a number of previously unreported auroral features that form shortly after the IMF B_z–component turns sharply northward. The auroral images were captured by the Boreal Aurora Camera Constellation (BACC) All-sky camera at the Kjell Henriksen Observatory, located in Longyearbyen, Svalbard. These observations are different from those previously reported. There are several differences: (a) The Eastward-Moving Auroral Forms (EMAFs) do not originate from type 1 or type 2 aurora. The EMAFs originate from a diffuse vertical auroral form in the far west part of the ASC image. Vertical refers to the auroral form oriented in the north-south direction in the frame of the ASC image. (b) The EMAFs form crescent shapes after they begin to drift eastward. (c) The EMAFs are discrete auroral forms; previously reported ionospheric signatures of high-latitude reconnection are described as patches of brightness that form within a pre-existing auroral band. (d) The EMAFs are observed to first move eastward and then slightly poleward during their journey. The movements of previously reported Ionospheric signatures of high-latitude reconnection are described as expanding patches of brightness within a pre-existing auroral band. (e) Some of the EMAFs brighten again after fading, during their northeastward drift across the field of view. (f) The EMAFs begin their eastward motion aligned in the north-south direction. During their northeast drift, they begin to tilt toward the east. Some of the EMAFs keep tilting until they are aligned in the east-west direction.