[P-EM10] Coupling Processes in the Atmosphere-Ionosphere System

[PEM10-11] Impact of the lower thermospheric winter-to-summer residual circulation on thermospheric composition

★Invited Papers

*Liying Qian¹, Jia Yue^2,3 (1.University Corporation for Atmospheric Research, 2.Center for Atmospheric Science, Hampton University, 3.ESSIC, University of Maryland College Park)

Keywords:Thermosphere Circulation, Thermosphere Composition, Ionosphere Winter Anomaly

Gravity wave forcing near the mesopause drives a summer-to-winter residual circulation in the mesosphere and a reversed, lower thermospheric winter-to-summer residual circulation. We conducted modeling studies to investigate how this lower thermospheric residual circulation impact thermospheric composition (O/N₂). We found that the upwelling associated with the residual circulation significantly decreases O/N₂ in winter and the downwelling in summer slightly increases O/N₂. Consequently, the residual circulation reduces the summer-to-winter latitudinal gradient of O/N₂, which causes the simulated latitudinal gradient of O/N₂ to be more consistent with observations. The smaller summer-to-winter latitudinal gradient of O/N₂ would decrease the ionosphere winter anomaly in model simulations, which would bring the simulated winter anomaly into better agreement with ionospheric observations. The lower thermospheric residual circulation may be a process that has been largely ignored but is very important to the summer-to-winter latitudinal gradients, as well as annual/semiannual variations in the thermosphere and ionosphere.