Thermospheric Gravity Waves and Ionospheric Disturbances Triggered by Mountain Waves Over the Western US in January 2017

Abstract

We analyze an episode of strong mountain wave (MW) activity over the western US from 9 to 12 January 2017 using the HIgh Altitude mechanistic General Circulation Model. We find that medium-scale MWs were generated by strong eastward flow over the Sierra Nevada and the Rocky Mountains. During this time, part of the stratospheric polar vortex jet extended from the western US to eastern Canada such that the MWs propagated into the lower mesosphere where they dissipated from westward vertical wind shear. This resulted in secondary gravity waves (GWs) that propagated into the lower thermosphere where tertiary GWs having concentric ring structures were created. With increasing altitude in the thermosphere, certain propagation directions were highlighted as a result of the dissipation induced by the tidal winds. At 260 km, we find eastward propagation during local morning over the northeastern US, equatorward propagation around local noon over the southern US, westward propagation during local afternoon over the northwestern US, and poleward propagation over Canada after local midnight. In addition, the model shows equatorward propagating larger-scale GWs over Canada from remote sources around local noon. The simulated regional GW-mean flow interaction patterns are consistent with multi-step vertical coupling triggered by the MWs. The traveling ionospheric disturbances (TIDs) during the MW event are simulated with the ionospheric model SAMI3. The simulated GWs and TIDs are consistent with the medium-to-large-scale TIDs observed over the continental US in GPS TEC data.