Ionosphere‐Thermosphere Coupling in the Northern Polar Region During the May 2024 Geomagnetic Superstorm

Abstract The May 2024 superstorm, as the most intense geomagnetic storm since 2003, caused a variety of disturbances in the magnetosphere‐ionosphere‐thermosphere system. This study investigates the long‐lasting electron density depletion in the polar region and the underlying ionosphere‐thermosphere coupling, based on a comprehensive set of observations from ground and space. Initially, a significant amount of solar wind energy was dissipated at high latitudes, and we estimate that the hemispheric Joule heating reached 1.25 TW by using a newly developed method that utilizes SuperDARN, SuperMAG, and AMPERE data. This intense heating increased the ion temperature by 500–1,200 K in the polar region, as detected by the EISCAT Svalbard radar (ESR). Furthermore, Joule heating caused significant upwelling of the polar thermosphere, evidenced by 300%–480% increase in neutral mass density and a substantial depletion in up to 50%, as observed by several low‐Earth‐orbit satellites. Both the increase in ion temperature and the change in neutral composition are crucial factors in accelerating the F ‐region recombination process. Consequently, the transition altitude of molecular to oxygen ions increased dramatically from 200 to 380 km, as detected by the ESR radar. The ultimate consequence was a severe depletion in electron density in the polar F –region ionosphere, reaching 70%–85% on 11 May, which gradually recovered over the next two days. Our analysis underscores the importance of simultaneous, multi‐instrument observations for a comprehensive understanding of the coupling chain during extreme geomagnetic disturbances.