Influence of Mesospheric Gravity Wave Drag on the Formation of Winter Helium Bulge in the Thermosphere

Abstract In this study, we focused on the influences of mesospheric gravity wave drag on the winter helium bulge in the thermosphere. The related physical mechanisms are investigated based on the three‐dimensional physics‐based Thermosphere‐Ionosphere‐Mesosphere Electrodynamic General Circulation Model. The simulation results suggested that the mesospheric gravity wave drag can contribute to the high amplitude of winter helium bulge due to the intensified summer‐to‐winter circulation in the thermosphere. It was found that the meridional pressure gradient force, which dominates the generation of thermospheric large‐scale circulation, shows an increase when the effect of mesospheric gravity wave drag is considered. The change in thermospheric pressure force is attributed to the mesospheric gravity wave drag related winter‐to‐summer flow in the lower thermosphere. This intensified summer‐to‐winter circulation in the thermosphere leads to the decrease and increase of helium concentration in summer and winter, respectively, which thus contributes to the thermospheric winter helium bulge under the effects of mesospheric gravity wave drag.