Effects of Energetic Electron and Proton Precipitations on Thermospheric Nitric Oxide Cooling during shock-led Interplanetary Coronal Mass Ejections

Satellite measurements have revealed significant enhancement of 5.3-µm nitric oxide (NO) emission during shock-led interplanetary coronal mass ejections (ICMEs). Great discrepancies in modeled neutral density occur during these events, and may be attributed to the abnormally high NO cooling. Meanwhile, the relative significance of protons, soft electrons, and keV-electrons to NO emission is yet to be well determined. The goal of this study is to identify the contribution of electron and proton precipitations to the thermospheric NO cooling by using the Defense Meteorological Satellite Program (DMSP) data. The observed energetic electrons and protons (0.1–30.2 keV) during 36 shock-led ICME events in 2002–2010 are binned into geomagnetic grids to provide statistical distributions of the particle precipitation for polar regions. The distributions are incorporated into the Global Ionosphere-Thermosphere Model. The results show that electrons play a dominant role to NO cooling, but protons are also important and contribute to up to a quarter of NO cooling by electrons and ions combined. NO cooling enhancement during the events is proportional to the level of energy flux and is dominated by the electrons in the energy band of 1.4–3.1 keV. Both total electron content (TEC) and NO cooling enhance at the source regions, but they have different lifetime and correlation with the particle precipitations. Generally, NO cooling and TEC enhancements have a positive correlation with the precipitating energy. Cross correlation shows that particle precipitations have more direct and instantaneous impact on TEC while it takes longer for the atmosphere to heat up for cooling to proceed.