Ground-based radar detection of the equatorward boundary of ion auroral oval in the dusk-midnight sector and its dynamical association with substorms

摘要

One of the important boundaries of the auroral region in the dusk-midnight sector is the equatorward boundary of the ion precipitation. In this region, on average, the ion precipitation region is equatorward of the electron precipitation region and is important in the overall energy budget. There are ground and satellite based measurement techniques to detect this important boundary but many of these measurements lack the temporal and spatial coverage required to study the dynamical features of this boundaries relationship with substorms. In this paper a review of a new ground based radar technique to determine the boundary and its limitations are presented. The new radar method is used to study the substorm growth phase dynamics. It found that on average, the boundary is located more equatorward during substorms than during non substorms. This implies that magnetotail stretching is a necessary condition for substorms. It is also found that statically there is no difference in the location of the boundary for substorms and non substorms in the 18-19 hours magnetic local time sector. The equatorward expansion rate of the boundary shows clear distinction between substorms and non substorms: The equatorward expansion rate of the boundary is much lower during non substorms than during substorms. Implications of the results for substorm dynamics are also presented.