DMSP Observations of High‐Latitude Dayside Aurora (HiLDA)

Abstract

AbstractWe report two events of high‐latitude dayside aurora (HiLDA), a large‐scale aurora in the dayside polar cap, observed by the Defense Meteorological Satellite Program (DMSP) spacecraft in the northern and southern hemispheres, respectively. While HiLDA in the northern hemisphere was reported before under interplanetary magnetic field (IMF) positive By conditions, we show for the first time a HiLDA event in the southern hemisphere when the IMF negative By component was dominant. Our observations also show that HiLDA is highly dynamical: change in its forms, size, location, and development of fine structures during its long lifetime of hours. The co‐occurrence of HiLDA and the duskside oval‐aligned transpolar aurora (TPA) may be a common feature during IMF By dominant conditions. Both are associated with the high‐latitude reconnection and the cusp. Based on the linear Knight relation, we estimate the distribution of the electron density in the magnetospheric source region of HiLDA. These results indicate that HiLDA maps most probably to the high‐latitude lobe tailward of the cusp, where the electron density is down to 0.03−3 cm−3. The lobe electrons are accelerated by the field‐aligned potential drop (up to 10 kV) set up in the poleward part of upward Region 0 field‐aligned current (FAC). The total energy flux of HiLDA electrons can be up to 50 mW/m2, indicating HiLDA precipitation as a potential energy source that impacts the polar ionosphere‐thermosphere system.