An empirical determination of proton auroral far ultraviolet emission efficiencies using a new nonclimatological proton flux extrapolation method

Abstract

Model‐derived electron and proton auroral FUV emission efficiencies of relevance to auroral FUV remote sensing methods are evaluated using coincident observations by Special Sensor Ultraviolet Spectrographic Imager (SSUSI) and Special Sensor J/5 (SSJ/5), both on board the Defense Meteorological Satellite Program (DMSP) satellite F16. This follows earlier work by Knight et al. (2008), which reported higher than expected proton Lyman‐Birge‐Hopfield (LBH) emission efficiencies based on F16 SSUSI and SSJ/5 comparisons, and Correira et al. (2011), which suggested a downward revision in the proton LBH efficiencies from Knight et al. (2008). These proton efficiency results rely on proton extrapolation methods to supply the unmeasured proton flux above 30 keV (the upper limit of SSJ/5). Correira et al. (2011) determined that there was a bias in the proton extrapolation method used by Knight et al. (2008) that was caused by column emission rate (CER) thresholding in the coincident SSUSI and SSJ/5 sets. In the latest work, a more robust proton flux extrapolation method is introduced which does not have the problem of CER threshold dependence. The new extrapolation method uses coincident SSUSI Lyman alpha observations to constrain the extrapolated proton flux above 30 keV in such a way that unknown Lyman alpha model yield errors and SSUSI and SSJ/5 calibration errors drop out without biasing the extrapolation. With the latest extrapolation method, SSUSI‐SSJ/5 comparisons indicate that proton aurora is typically a factor of ∼4.5 more efficient per unit of energy flux in producing LBH than electron aurora.