Impact of the lower thermospheric winter-to-summer residual circulation on thermospheric composition

We conducted modeling studies to investigate how this lower thermospheric residual circulation impacts thermospheric composition (O/N-2). We found that the upwelling associated with the residual circulation significantly decreases O/N-2 in winter and the downwelling in summer slightly increases O/N-2.

Consequently, the residual circulation reduces the summer-to-winter latitudinal gradient of O/N-2, which causes the simulated latitudinal gradient of O/N-2 to be more consistent with observations. The smaller summer-to-winter latitudinal gradient of O/N-2 would decrease the ionosphere winter anomaly in model simulations, which would bring the simulated winter anomaly into better agreement with ionospheric observations.