Effects of Gravity Waves on the thermosphere during Stratospheric Sudden Warming simulated by an atmosphere-ionosphere coupled Model.

Abstract:

It has been recognized that gravity waves play an important role on the momentum and energy balance in the thermosphere. Using a whole atmosphere-ionosphere coupled model (GAIA), effects of upward propagating gravity waves on the general circulation in the thermosphere are studied. The GAIA contains the region from the ground surface to the upper thermosphere, so that we can simulate excitation of gravity waves in the lower atmosphere, their upward propagation to the thermosphere, and their impact on the general circulation in the thermosphere. We have recently developed an atmosphere-ionosphere coupled model with high horizontal resolution (about 1 degree longitude by 1degree latitude). In this study, we focus our attention on behaviors of gravity waves in the mesosphere and thermosphere during stratospheric sudden warming event (SSW). The changes of the zonal mean zonal wind in the stratosphere during SSW alter propagation condition of gravity waves from the lower atmosphere to the upper atmosphere. This means that SSW affects behaviors of thermospheric gravity waves. Our simulation result indicates that gravity wave drag in the thermosphere of the winter hemisphere is strongly influenced by SSW. This change of the gravity wave drag also modifies the mean meridional circulation and atmospheric composition in the thermosphere. The impact of the thermospheric gravity wave on the ionosphere during SSW is also discussed.