Afternoon subauroral proton precipitation resulting from ring current—plasmasphere interaction

Abstract

We investigate the occurrence of arcs of precipitating protons equatorward of and detached from the afternoon proton auroral oval and their relationship with the plasmasphere and electromagnetic ion cyclotron waves. In a four month study interval including sixteen events, we find that the detached proton arcs are more likely to occur during geomagnetically disturbed periods and specifically at times when enhanced energetic ion densities and temperature anisotropies are observed in the equatorial magnetosphere. The disturbance-time arcs tend to be located at lower magnetic latitudes and are consistently associated with plasmaspheric plumes. Conversely, arcs which occur during quiet times tend to be located at higher latitudes, and their relationship with regions of enhanced cold plasma density remains unclear. Wave data available for two of the detached arc events indicate the presence of strong ion cyclotron waves near the equator in the vicinity of the proton precipitation region.