Direct comparison of transverse ion acceleration mechanisms in the auroral region at solar minimum

Abstract

Previous studies have shown that most ion conies in the auroral zone are associated with either broadband extremely low frequency (BBELF) or electromagnetic ion cyclotron (EMIC) emissions. EMIC emissions, which are correlated with preferential acceleration of He + , are concentrated in the premidnight sector; BBELF emissions, which are found at all local times, are not associated with preferential acceleration of any species. We present a case study of five auroral passes which include ion conies associated with EMIC and BBELF waves at different locations. Our data indicate that EMIC waves can be locally important for accelerating outflowing He + in the aurora. However, although this study's design exaggerates the contribution of EMIC waves to transverse ion acceleration, we find in each case that BBELF waves produce higher energy fluxes of upflowing ions. Therefore, events with BBELF emissions dominate the overall ion outflow.