Impacts of Gravity Waves on the Thermospheric Circulation and Composition

The high-resolution Whole Atmosphere Community Climate Model with thermosphere/ionosphere extension (WACCM-X) is used to study the impacts of gravity waves (GWs) on the thermospheric circulation and composition. The resolved GWs are found to propagate anisotropically with stronger eastward components at most altitudes. The dissipation of these waves in the thermosphere produces a net eastward forcing that reaches peak values between 200 and 250 km at mid-high latitudes in both hemispheres. Consequently, the mean circulation is weakened in the winter hemisphere and enhanced in the summer, which in turn impacts the thermospheric composition. Most notably, the column integrated O/N2 in both hemispheres is reduced and agrees better with observations. The mean thermospheric GW forcing in the meridional direction has comparable amplitude and acts to modify the gradient-wind relationship. Small-scale waves originate from the lower atmosphere have been shown to propagate into the thermosphere. To study their effects a high-resolution whole atmosphere model has been employed. Using this high-resolution model, which can partially resolve the small-scale waves, we can directly quantify the force exerted by these waves on the general circulation in the thermosphere. We found that such force is strong, and affects the thermospheric circulation in both winter and summer hemisphere. This consequently changes the distribution of important thermospheric species. One measure of the thermospheric composition is the ratio of atomic oxygen and molecular nitrogen, which is an indicator of the relative abundance of atomic and molecular species. This ratio has been grossly over-estimated in previous modeling studies. It is reduced as a result of the circulation change, and is much better agreement with observations. Gravity waves (GWs) resolved by high-resolution WACCM-X displays anisotropic propagation GW forcing alters thermospheric circulation The circulation change leads to a much improved thermospheric O/N2