Coupling between the lower and upper atmosphere in Whole Atmosphere Model (WAM) simulations

The Whole Atmosphere Model is being developed to study and forecast the effects of dynamical perturbations generated in the lower atmosphere at various temporal and spatial scales on the upper atmosphere and ionosphere. With applications to space weather prediction in mind, WAM is built on National Weather Service's operational weather prediction Global Forecast System (GFS) extended from its nominal top altitude of 62 km to about 600 km. The model extension into a domain of highly variable composition, high temperatures, and very low density requires certain generalization of the common meteorological model framework. WAM also incorporates all relevant physical processes including those responsible for the generation of tidal and planetary waves in the troposphere and stratosphere. In the absence of artificial boundaries within the model domain these waves freely propagate into the upper atmosphere, growing in amplitude and interacting non-linearly, to eventually dissipate by various physical processes. Long-term simulations reveal realistic seasonal variability of tidal waves with a substantial contribution from non-migrating tidal modes, recently implicated in the observed morphology of the ionosphere. WAM is the first model to realistically reproduce such long observed phenomena as the prominent Midnight Temperature Maximum (MTM), as well as other nocturnal features in thermospheric temperature and density recently identified both in satellite and ground-based observations. Model diagnostics revealing their relation to tidal waves propagating from the lower atmosphere will be presented.