Analysis of thermospheric and ionospheric variations during recent solar storms in 2024 in the framework of the project CASPER

The project CASPER is an interdisciplinary collaboration between the Institute of Geodesy and the Institute of Physics and is funded by the Austrian Research Promotion Agency. It deals with the influence of solar eruptions such as coronal mass ejections and solar flares on the Earth's neutral atmosphere and ionosphere. In this study we focus on the most severe geomagnetic storms that occurred in solar cycle 25. This includes the effects of the extreme "Gannon storms" on 10/11 May, as well as solar eruptions that occurred in August and October in 2024. We present a detailed analysis of various interplanetary and terrestrial measurements to allegorise the individual solar storms. For the thermospheric variations, the analysis is based on observations from the GRACE-FO and SWARM satellite missions using accelerometer and kinematic orbit data. On this basis, we are able to present changes in the Earth's neutral in terms of satellite orbit decays. Regarding the ionosphere, the part of the Earth’s atmosphere where solar radiation ionizes the atoms and molecules, we present the latest implementations in our software GROOPS. The slant total electron content (STEC) parameter is determined using a least-squares adjustment approach. To enhance the accuracy, high-order ionospheric correction terms are integrated into the estimation process. This information allows the derivation of additional ionospheric parameters, such as vertical total electron content (VTEC), for various altitude layers to be comparable with neutral density estimates. Finally, in terms of the predictability of the impact of solar eruptions on the satellite altitude, we also present the current status of the SODA forecast service which is part of the ESA's Space Safety Programme Ionospheric Weather Expert Service Centre (I.161).