Darkness Breaks the Silence: Effects of the December 2021 Solar Eclipse on Geospace Using Numerical Simulations*

Solar eclipses provide a unique opportunity to study the Geospace environment. On December 04, 2021, a total solar eclipse occurred over Antarctica that lasted about three hours. While the effect of solar radiation on the Earth's upper atmosphere is rapidly turned off and on, how a solar eclipse influences the magnetosphere-ionosphere-thermosphere (M-I-T) dynamics by changing the solar radiation-induced ionospheric conductance has not been fully investigated. In addition, the sudden change in ionospheric conductance may also cause significant inter-hemispheric asymmetry (IHA) in Geospace. In this study, based on solar observations, we generated eclipse-induced radiation distribution, i.e., eclipse masks. By applying these masks, the Global Ionosphere-Thermosphere Model (GITM) with NCAR 3Dynamo module is utilized to specify the ionospheric conductance for the magnetosphere. Utilizing the BATS-R-US Magnetohydrodynamics model, the impacts of the eclipse-induced ionospheric conductance changes on the global M-I-T coupled system and their subsequent influences on the upper atmosphere have been assessed. We focus on the following aspects: 1) Solar eclipse-induced depletion of conductance and its impacts on ionospheric electric currents and potential in the polar and auroral regions; 2) IHA as captured in the coupled M-I-T system in response to the eclipse; and 3) The feedback interaction between the magnetosphere and the upper atmosphere induced by the solar eclipse will also be investigated using GITM. Our studies will help quantify the significance of solar eclipse on the entire Geospace environment.