Abstract: Atmospheric gravity waves (GWs) are created in the troposphere from wind flow over mountains, and in the stratosphere below the maximum of the polar vortex from imbalance of the polar vortex. Because these GWs are slow, they cannot propagate directly to the thermosphere due to dissipation from breaking/critical level filtering and molecular viscosity. Additionally, most primary GWs from deep convection and the Tonga eruption break/dissipate below z=200 km, thereby exciting secondary GWs that propagate within the F region. In this talk, we illuminate the process of multi-step vertical coupling, which is the process whereby momentum and energy are deposited in the atmosphere where a wave breaks/dissipates, thereby creating local body forces/heatings that excite higher-order GWs. This results in secondary, tertiary and higher-order GWs in the thermosphere from lower atmospheric sources (such as mountain waves, the polar vortex and even deep convection). Depending on the intrinsic horizontal phase speeds of the secondary GWs, this process can occur multiple times from primary GWs in the troposphere/stratosphere to GWs in the middle to upper thermosphere.
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