Figure Caption: Snapshot of gravity waves (relative temperature perturbations, colors) and the large-scale horizontal wind (arrows, scale in the lower left corner) in the thermosphere on 11 January 2016 (1:30 UT) as simulated with the HIAMCM nudged to MERRA-2 reanalysis. A large concentric ring structure is centered over Europe. These are tertiary gravity waves that propagate roughly against the large-scale wind and have horizontal phase speeds of several 100 m/s.
Model Description: The High Altitude Mechanistic general Circulation Model (HIAMCM) extends from the surface to an altitude of about 450 km. The model is based on a standard spectral dynamical core and has a high spatial resolution (equivalent horizontal grid spacing of 52 km; vertical level spacing of 600 below ~130 km, larger at higher altitudes). This resolution is combined with an advanced parameterization of macro-turbulent horizontal and vertical diffusion, including molecular viscosity in the thermosphere. As a result, gravity waves (GWs) are simulated explicitly over the whole altitude range. Due to the explicit simulation of the generation, propagation, and dissipation of GWs, the HIAMCM captures the multi-step vertical coupling associated with secondary and tertiary GWs. This coupling mechanism is essential for GW dynamics in the thermosphere, which is a major aspect of the WAVE DRIVE Science Center.
