Correspondence between a plasma-based EMIC wave proxy and subauroral proton precipitation

Abstract

The loss of relativistic electrons from the Earth's radiation belts as a result of resonant interactions with electromagnetic ion cyclotron waves (EMIC) waves has yet to be fully quantified, in part, due to the lack of global measurements of the wave distribution during individual storm events. Recent work has focused on augmenting direct wave measurements with proxy wave indicators. Here we compare two different techniques for inferring the presence of EMIC waves: 1) a wave-growth proxy and amplitude estimate based on in situ plasma measurements of the cold and hot ion distributions, and 2) FUV observations of subauroral proton precipitation, which is thought to result from interactions with EMIC waves. For two event intervals, we show good correspondence between proxy predictions of wave growth, calculated using measurements from geostationary spacecraft, and precipitation observed at the northern hemisphere ionospheric footprint. Further, for times when the proxy is positive, we observe a moderate positive correlation (r = 0.56) between the predicted wave amplitude and the mean FUV brightness in a 300-km circle about the footprint. Further development and verification of these techniques will enhance our ability to infer the global distribution of EMIC waves when direct measurements are not available. Copyright 2011 by the American Geophysical Union.