Middle-Atmosphere Mountain Waves and Drag Near the Drake Passage: Observations, mini-MIP, and an OSSE

<p>Orographic gravity wave (OGW) drag is one of the fundamental physics parametrizations employed in every global numerical model across timescales from weather to climate. These parameterizations have significant influences, both direct and indirect, on the atmosphere’s general circulation from the troposphere at least through the mesosphere. Despite their significant influence, observational constraints on these parameterizations are still largely lacking.</p><p>Presented here is a team project jointly supported by SPARC and the International Space Science Institute with the overall objective of providing new quantitative constraints for OGW drag parameterizations. Specific objectives are to evaluate methods that quantify vertical fluxes of horizontal momentum (MF) from satellite observations via an observing system simulation experiment (OSSE), a validation of WRF, UKMO, ECMWF, and ICON models against satellite and balloon observations, and an inter-comparison of OGW properties (e.g. MF and drag) within these models. Evaluation of satellite-based estimates of MF and model validation/inter-comparison will help to better quantify actual MF in the stratosphere, providing the best stratospheric MF and drag estimates for parameterizations to reproduce to date.</p><p>Two unique aspects of the project are that all models involved are deep, extending up to 1 Pa. The motivations for doing so was to include entire instrument weighting functions for AIRS observations, allowing direct, quantitative comparison between AIRS (and other satellite-borne) observations and the models. The second is the effort to perform an OSSE within the simulations, allowing comparison between MF from satellite-based methods within the models to the true MF in the models.</p><p>Preliminary results show that higher-res models (dx = 3 km) compare well and produce significantly more MF than lower-res global models, but the higher-res models still underrepresent OGW amplitudes. Mesospheric tides in analyses used to force the models significantly modulate resolved GWs and their drags.</p>