Abstract
Four state-of-the-science numerical weather prediction (NWP) models were used to perform mountain wave (MW)-resolving hindcasts over the Drake Passage of a 10-day period in 2010 with numerous observed MW cases. The Integrated Forecast System (IFS) and the Icosahedral Nonhydrostatic (ICON) model were run at Delta x approximate to 9 and 13 km globally.
TheWeather Research and Forecasting (WRF) Model and the Met Office Unified Model (UM) were both configured with a Dx 5 3-km regional domain. All domains had tops near 1 Pa (z approximate to 80 km).
These deep domains allowed quantitative validation against Atmospheric Infrared Sounder (AIRS) observations, accounting for observation time, viewing geometry, and radiative transfer. All models reproduced observed middle-atmosphere MWs with remarkable skill.
Increased horizontal resolution improved validations. Still, all models underrepresented observed MW amplitudes, even after accounting for model effective resolution and instrument noise, suggesting even at Delta x approximate to 3-km resolution, small-scale MWs are underresolved and/ or overdiffused.
MWdrag parameterizations are still necessary in NWP models at current operational resolutions of Delta x approximate to 10 km. Upper GW sponge layers in the operationally configured models significantly, artificially reduced MW amplitudes in the upper stratosphere and mesosphere.
In the IFS, parameterized GW drags partly compensated this deficiency, but still, total drags were approximate to 6 times smaller than that resolved at Delta x approximate to 3 km. Meridionally propagating MWs significantly enhance zonal drag over the Drake Passage.
Interestingly, drag associated with meridional fluxes of zonal momentum (i.e., (u'v') over bar) were important; not accounting for these terms results in a drag in the wrong direction at and below the polar night jet.