Nightside detached auroras due to precipitating protons/ions during intense magnetic storms

Abstract

Nightside detached auroras (NDA) during intense magnetic storms are studied by using FUV image data from Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics (TIMED)/Global Ultraviolet Imager (GUVI), Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE)/FUV, and particle data from DMSP/SSJ/4 instruments. We found that NDA are caused by proton/ion precipitation only. Thin arc‐shaped NDA are very likely due to soft (<1 keV) proton/ion precipitation. Thick or patch‐shaped NDA are caused by energetic (∼10 keV) proton/ion precipitation. All the cases indicate that the NDA were observed when Dst was less −130 nT. More specifically, the NDA occurred during recovery or the lowest Dst period for each intense storm. The magnetic latitudes of the NDA are between 45° and 55° (L shell: 2.0–3.0). We found that the latitude location of the NDA is quasi‐linearly correlated with Dst. The magnetic local time (MLT) of the NDA ranges from 1930 to 0300. All the facts indicate that the source of the NDA is the trapped protons/ions in the ring current. Precipitation of the trapped protons/ions is caused by an interaction between the perpendicularly heated ring current particles and the cold/dense plasma at the plasmapause.