Joint EOL/CGD Seminar: Chris Kruse - Evaluating gravity wave drag parameterizations in the middle

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Title: Evaluating gravity wave drag parameterizations in the middle atmosphere using wave-resolving simulations of observed events

Abstract: Atmospheric gravity waves (GWs) are small-scale (10-1000-km) buoyancy oscillations that transport energy and momentum, which get deposited wherever these waves dissipate. As their scales are under- and un-resolved in weather and climate models, parameterizations are used to primarily represent GW momentum deposition, which forces the resolved flows. This parameterized forcing is significant in Earth’s general circulation directly and indirectly, with significant direct effects in the middle and upper atmosphere where low densities force GW breaking and force more significant accelerations of the flow. Still, GW parameterizations are highly idealized, often tuned, and not well-constrained. Observations are sparse and/or indirect. Mesoscale models are a powerful tool to understand GW physics and constrain parameterizations; however, quantitative evaluation of their simulations against what observations exist is challenging.

Here, two efforts to model observed stratospheric GWs, one forced by orography and one forced by deep convection, are presented. The modeled GWs are quantitatively compared against Atmospheric InfraRed Sounder (AIRS) observations. Current, state-of-the-science mesoscale models can reproduce observed orographic GWs in the middle atmosphere with skill when terrain scales and the GWs they force are well-resolved. Encouragingly, if convective diabatic heating is provided to a GW-resolving model at the correct places and times, models can produce middle-atmosphere GWs that compare well against AIRS observations as well. Detailed analysis of these validated simulations suggests future development of GW parameterizations should include all wave scales, lateral propagation, as well as temporal effects.