Nightside thermospheric FUV emissions due to energetic neutral atom precipitation during magnetic superstorms

TIMED/GUVI detected anomalous FUV emissions from the nightside thermosphere over a wide latitude range, from the subauroral latitudes to the equatorial regions during each of three magnetic superstorms (29–31 October 2003, 20 November 2003, and 7–10 November 2004). We note that during the one case (7–10 November 2004) where there were coincident measurements of the flux of energetic particles as observed by IMAGE HENA, the FUV intensity (as seen in five bandpasses or “colors”: 121.6 nm, 130.4 nm, 135.6 nm, LBHS (140–150 nm) and LBHL (165–180 nm)) showed qualitative agreement with the behavior of the energetic neutral atoms (ENA). This suggests that the source of the FUV emissions is the ENA originating from the ring current. We also found that for all three storms we studied that the FUV intensities are well correlated with Dst . The intensity in all colors is observed to increase with latitude up to the auroral oval. Except for 121.6 nm, the observed intensities exhibit a sharp decrease near the magnetic equator region. The origin, location, and spatial extent of the FUV emissions is quite different from that of the traditional aurora, we find that this phenomena is consistent with neutral particle precipitation. We call this signature of the coupling of the ring current and the thermosphere the neutral particle aurora.