Impacts of Ionospheric Conductance During the December 2021 Solar Eclipse on the Coupled Magnetosphere-Ionosphere-Thermosphere System

Solar eclipses provide unique opportunities to investigate geospace dynamics driven by rapid, localized reductions in solar radiation. On December , 2021, a total solar eclipse occurred over West Antarctica during substorms. While eclipse effects on Earth's upper atmosphere are widely studied, their subsequent impact on the magnetospheric configuration and feedback loops are less explored. Abrupt changes in conductivity can also affect interhemispheric asymmetry (IHA). In this study, an eclipse EUV mask was applied in the Global Ionosphere-Thermosphere Model (GITM), driven by different high-latitude forcing specifications. Using the Space Weather Modeling Framework, we examined how eclipse-induced ionospheric conductance changes impact the magnetosphere and feed back to the I-T system. Results show a -similar to 30% reduction in total electron content and -similar to 35% drop in ionospheric conductance compared to the no-eclipse case, consistent with observations. This leads to an enhanced cross-polar cap potential (CPCP) in both hemispheres (north vs. south: 36 vs. 40 kV). The eclipse reduced IHA in total field-aligned currents and CPCP, bringing asymmetry close to zero after the shadow passed over the polar region. The magnetosphere also showed dynamic responses, including changes in plasma pressure and flow that shifted the magnetotail by up to 16 in the X-direction. Finally, by driving GITM with eclipse-modified magnetospheric forcing, we found that magnetospheric feedback amplified thermospheric wind perturbations over the polar cap, even exceeding the direct effect of reduced solar EUV. These results demonstrate the critical role of ionospheric conductance in the coupled M-I-T system during solar eclipses.