Investigation of the Southern Hemisphere Mid-High Latitude Thermospheric Sigma O/N-2 Responses to the Space-X Storm

The geomagnetic storm on February 3, 2022 caused the loss of 38 Starlink satellites of Space-X. The Global-scale Observations of the Limb and Disk (GOLD) observations and Multi-Scale Atmosphere Geospace Environment (MAGE) model simulations are utilized to investigate the thermospheric composition responses to the Space-X storm. The percentage difference of the GOLD observed thermospheric O and N-2 column density ratio (Sigma O/N-2) between the storm time (February 3, Day-of-Year [DOY] 34) and quiet time (DOY 32) shows a depletion region in the local noon sector mid-high latitudes in the southern hemisphere, which corresponds to the east side of GOLD field-of-view (FOV). This is different from the classic theory of thermospheric composition disturbance during geomagnetic storms, under which the Sigma O/N-2 depletion is usually generated at local midnight and high latitudes, and thus, appear on the west side of GOLD FOV. MAGE simulations reproduce the observations qualitatively and indicate that the Sigma O/N-2 depletion is formed due to strong upwelling in the local morning caused by strong Joule heating. Interestingly, enhanced equatorward winds appear near local midnight, but also in the local morning sector, which transports Sigma O/N-2 depletion equatorward. The depletion corotates toward the local afternoon and is observed in the GOLD FOV. The equatorward winds in the local morning are due to the ion-neutral coupling under the conditions of a dominant positive interplanetary magnetic field east-west component (B-y) during the storm.