jgr paper data

Dawn–Dusk Asymmetry of Thermospheric ΣO/N₂ Depletion During Geomagnetic Storms Observed by FengYun-3E Fang Jiang1,2,3, GuoYing Jiang1, 5,6,7 , Tian Mao 4, Qian Song 4, LiPing Fu 1,2,3*,Nan Jia1,2,3, TianFang Wang 1,2,3 1 National Space Science Center, Chinese Academy of Sciences, Beijing, China 2 Beijing Key Laboratory of Space Environment Exploration, Beijing, China 3 Key Laboratory of Environmental Space Situation Awareness Technology, Beijing, China 4 National Satellite Meteorological Center, China Meteorological Administration, Beijing, China 5 State Key Laboratory of Solar Activity and Space Weather, National Space Science Center, Chinese Academy of Sciences, China 6 School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing, China 7 National Field Observation and Research Station (Hainan) for Space Weather, Hainan, China Abstract A pronounced dawn–dusk asymmetry in the thermospheric column oxygen-to-molecular nitrogen ratio (ΣO/N₂) depletion during geomagnetic storms is revealed by observations from the Triple Ionosphere PhotoMeter (TRIPM) onboard the dawn–dusk orbiting FengYun-3E (FY-3E) satellite. Observations show that storm-induced ΣO/N₂ depletion at Northern Hemisphere mid-latitudes is consistently stronger in the dawn sector than in the dusk sector across all three investigated spring/summer events spanning moderate, severe, and extreme storm intensities. Simulations using the Thermosphere–Ionosphere Electrodynamics General Circulation Model (TIE-GCM), sampled along the actual TRIPM orbital tracks, reproduce the observed dawn-favoring asymmetry in all three events. Diagnostic analyses reveal a pronounced local-time contrast in horizontal neutral-wind advection, with stronger equatorward transport extending into the mid-latitude dawn sector. Controlled IMF By sensitivity experiments for the April 2023 storm further show that the dawn-dominant depletion persists under positive, negative, and zero By conditions, indicating that IMF By modulates the magnitude of the asymmetry rather than being a prerequisite for its occurrence. Dynamically, strong equatorward meridional winds persist on the dawn side across the examined storms and By conditions, providing a robust cross-latitude transport pathway, while the vertical and zonal wind responses are strongly modulated by IMF By. Positive By is associated with enhanced dawnside Joule heating, higher neutral temperatures, and stronger high-latitude vertical upwelling, coincident with an enhanced main-phase dawn–dusk depletion contrast. In comparison, the dusk sector exhibits a distinct circulation and thermal environment characterized by predominantly westward zonal winds, lower neutral temperatures, and persistent NO 5.3 μm radiative cooling. These results demonstrate that the dawn-favoring ΣO/N₂ depletion is associated with a persistent local-time asymmetry in neutral transport, while IMF By further modulates its magnitude through the reorganization of storm-time dynamical and thermodynamic responses.