Abstract: The thermosphere is an atmospheric region from ~100 km to ~1000 km produced by the atmospheric absorption of solar UV and EUV radiation. It is the region where atmospheric species is not well mixed but diffuses with its own scale height. The thermosphere is an open system changing greatly due to the energy and momentum deposition from the magnetosphere above and the waves from the lower atmosphere. In this talk, we will first discuss the dynamic processes driving the thermospheric responses to geomagnetic storms, including global 3-D redistribution of energy and momentum, and the interaction between the thermosphere and the ionosphere that is embedded in the thermosphere. We will then, as an example, investigate the responses of the thermosphere to the recent May 10, 2024 super storm. The Global Observations of Limb and Disk (GOLD) mission observed significantly large, global perturbations in thermospheric composition and temperature during the storm due to enormous energy and momentum inputs from the solar wind and magnetosphere. Thermospheric composition ratio (ΣO/N2) was depleted greatly from high to lower latitudes, associated with an enhanced neutral temperature. The composition ratio, however, was increased in the equatorial region with minor temperature changes. The GOLD synoptic images of ΣO/N2 and neutral temperature (at ∼160 km) also show, for the first time, a spatial vortex structure in ΣO/N2 perturbations in both hemispheres during the storm. These storm-induced, meso- to large scale thermospheric changes are simulated with a fully coupled whole geospace (Multiscale Atmosphere-Geospace Environment) model developed by the NASA Center for Geospace Storms (CGS). The MAGE model reproduced the GOLD observed ΣO/N2 vortex in the southern America and its evolution, but not in the northern American where the model appeared to overestimate the high-latitude Joule heating. The model results show that the southern hemisphere ΣO/N2 vortex was associated with the wind vortex, developed at high latitudes and was transported to lower latitudes where it dissipated.
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