Generation of transient dayside subauroral proton precipitation

Abstract

The Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE) spacecraft obtained the first global images of the proton aurora. One of the discoveries from these images was a region of proton precipitation equatorward of the nominal auroral oval. This precipitation can be observed for ∼10 min immediately following a large solar wind pressure pulse. Various mechanisms have been proposed for producing this precipitation. This study focuses on one of the proposed mechanisms, the scattering and precipitation of protons due to interaction with electromagnetic ion cyclotron (EMIC) waves. Using data from the IMAGE spacecraft FUV and EUV imagers, in situ ring current data from the Los Alamos geosynchronous spacecraft, and in situ solar wind data from the ACE spacecraft, two features of the precipitation, the local time occurrence and limited latitudinal extent, are explained. The local time occurrence of the precipitation is correlated with the orientation of the pressure pulse front in the solar wind. The limited latitudinal extent of the emissions appears to be related to the interaction between the hot ring current protons and the cold plasmaspheric ions that gives rise to EMIC wave growth.