Evidence of Potential Thermospheric Overcooling During the May 2024 Geomagnetic Superstorm

[During intense geomagnetic storms, the rapid and significant production of nitric oxide (NO) followed by its associated infrared radiative emission in lower thermosphere contributes crucially to the energetics of the upper atmosphere. This makes NO infrared radiative cooling a very important phenomenon which needs to be considered for accurate density forecasting in thermosphere. This study reports the investigation of variations in thermospheric density, and NO radiative cooling during the recent geomagnetic superstorm of May 2024. A very rare post‐storm thermospheric density depletion of about −23% on May 12 was observed by Swarm‐C in northern hemisphere in comparison to the prestorm condition on May 9. This overcooling was observed despite the continuous enhancement in solar EUV (24–36 nm) flux throughout the event. The thermospheric NO infrared radiative emission in the recovery phase of the storm is likely to be the plausible cause for this observed post‐storm density depletion. Our analysis also suggests an all time high thermospheric NO radiative cooling flux up to 11.84 ergs/cm2 ${\text{ergs/cm}}^{2}$/sec during May 2024 geomagnetic superstorm, which has also been compared with famous Halloween storms of October 2003]. Plain Language Summary The changing heat budget of upper atmosphere due to enhanced Joule heating, energetic particle precipitations, and NO infrared radiative cooling during geomagnetic storms may also modulate other atmospheric and ionospheric parameters that indirectly affect human life at the surface. Some examples are, thermospheric density and associated Lower Earth Orbit (LEO) satellite drags (which are particularly used for geophysical imaging), GPS navigation, exposure of thermospheric particles near ISS (International Space stations), etc. All these aspects need to be considered for a better space weather future. In this study, the variation in thermospheric density, and thermospheric NO radiative cooling have been investigated during the recent geomagnetic superstorm of May 2024. This study infers that the very enhanced NO radiative cooling in the recovery phase of this storm may have also contributed to the thermospheric density depletion in the post‐storm periods. The NO radiative cooling during this storm has also been compared with Halloween storms of October 2003. Key Points An all time high thermospheric NO radiative cooling flux is observed during the recent May 2024 geomagnetic superstorm A potential post‐storm th