Polar Ionosphere-thermosphere coupling during the May 2024 geomagnetic superstorm

In May 2024, the most intense geomagnetic storm since 2003 was caused by coronal mass ejections from the Sun. It has triggered a surge of interest within the international space science community with dedicated workshops and planned special issues. Our study focuses on the ionosphere-thermosphere responses in the northern polar region based on multiple observations from the ground-based instruments (including the EISCAT incoherent scatter radar on Svalbard, GNSS TEC receivers, SuperMAG magnetometers, and SuperDARN coherent scatter radars) and satellites (including the Swarm, GRACE-FO, TIMED, and DMSP satellites). The EISCAT Svalbard radar, GNSS TEC, and satellite observations showed strong and large-scale ionospheric electron density depletion over the northern polar ionosphere. During the superstorm, strong solar wind energy input was dissipated at high latitudes. We apply a new method to estimate the integral Joule heating power using SuperDARN, SuperMAG and AMPERE data. The result showed the Joule heating power was up to 1300 GW. The strong heating increased the ion temperature as observed by the EISCAT Svalbard radar. The ion-chemistry-coupled  EISCAT  analysis  showed  how the transition altitude from molecular ions to O+ was increased from 200 km to 380 km during the main and recovery phases of the storm. The strong heating also induced an upwelling of the thermosphere in the polar region as evidenced by the strong increase in the neutral mass density observed from the Swarm and GRACE-FO satellites and the strong depletion of ΣO/N2 by GUVI onboard TIMED. The changes both in ion temperature and neutral composition affected the F-region recombination and caused a long lasting strong depletion up to 80 % in the electron density in the polar ionosphere on 11 May 2024.