Latitudinal Distribution of Thermospheric Nitric Oxide (NO) Infrared Radiative Cooling During May and October 2024 Geomagnetic Storms

Abstract

Nitric oxide (NO) radiative cooling, seen as infrared emissions, plays an important role in the energy budget of thermosphere during geomagnetic storms. These emissions serve as a significant heat sink for the thermosphere and facilitate its recovery from the enhanced density and kinetic energy caused by increased Joule heating. Hence, the knowledge of latitudinal distribution of these emissions becomes significant considering the importance of the recovery time duration of the global thermosphere as a consequence of geomagnetic storms. This study discusses the dominating role of storm induced meridional winds, generated due to the Joule heating in the polar regions, in controlling the latitudinal distribution of NO infrared radiative cooling emissions during the two most severe geomagnetic storms of the $25th$ solar cycle (10–11 May, and 10–11 October 2024). During the May 11 event, the peak NO infrared radiative cooling events shifted from the high-latitudes (30–83 $°$N) to low-latitude (10 $°$S–30 $°$N) regions, whereas for the October 11 event, most of the emissions were located in 30–83 $°$N, and 0–52 $°$S latitude regions. The roles of background seasonal winds, and their associated compositional changes, and the solar energetic radiation (Extreme Ultraviolet or EUV) in modulating the latitudinal variations in the thermospheric NO infrared radiative cooling during both these events, and their consequences for space weather studies are presented.