Dawn–dusk asymmetry of MLT middle- and low-latitude temperature responses to super geomagnetic storms

At high latitudes, storm-time temperature enhancements in the mesosphere and lower thermosphere (MLT, ∼90–110 km) typically exhibit a pronounced dawn–dusk asymmetry, characterized by weaker warming on the dawn side and stronger warming on the dusk side. However, whether similar patterns and their underlying mechanisms extend to mid- and low latitudes remains unclear. Using the Whole Atmosphere Community Climate Model, this study investigates the atmospheric dynamical and thermodynamical variations during the Mother's Day superstorm (10–14 May 2024). The simulations reveal that in the mid- to low-latitude MLT regions, the dawn side warms by over 40 K while the dusk side stays under 20 K, with the Southern Hemisphere warming more overall but the Northern Hemisphere exhibiting a sharper dawn–dusk contrast. These results agree well with measurements from the Sounding of the Atmosphere using Broadband Emission Radiometry instrument aboard the Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics satellite. Moreover, the simulations further reveal that the pronounced dawn-side heating is driven by steady, storm-induced downward winds powered by a continuous equatorward meridional flow that persists even as the storm weakens, whereas dusk-side downflows are brief and reverse during recovery due to competing wind patterns. To our knowledge, this study is the first to identify the physical mechanisms underlying the opposing dawn–dusk asymmetry in storm-time MLT temperature responses at mid-low and high latitudes, offering new insight into MLT dynamics under extreme space weather and potentially facilitating the advancement of predictive models.