Doppler Shifted Auroral Hydrogen Lyman‐Alpha Spectra Observed by DMSP/SSUSI

Abstract

AbstractProton auroras, when viewed from space, are subjected to Doppler red shifts. Reports on space‐based observations of Doppler shift of H Lyman‐alpha (Ly‐α) spectral line associated with proton precipitation are still scarce. This study, as a first attempt, extracts Doppler shifted H Ly‐α spectral profiles resulting from proton precipitation from data acquired with the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) on board the Defense Meteorological Satellite Program (DMSP)/F16 spacecraft. SSUSI consists of a scanning imaging spectrograph, which covers the far ultraviolet spectrum from ∼1,120 to 1,850 Å, with 160 spectral bins and a spectral resolution of ∼20 Å. We show redshift Ly‐α spectra observed by SSUSI when its field of view traverses the auroral ovals. The inferred proton energy and energy flux are in close agreement with the DMSP SSJ in situ particle measurements. This study demonstrates the potential capability of SSUSI in monitoring the energetics of proton precipitation.