The NRL Mountain Wave Forecast Model (MWFM) [Preprint]
NAVAL RESEARCH LAB WASHINGTON DC E O HULBURT CENTER FOR SPACE RESEARCH
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The Department of Defense has a large and increasing investment in high-altitude long-endurance HALE reconnaissance aircraft. HALE aircraft have lightweight broad-winged designs, enabling them to reach stratospheric altitudes. These properties make them both aerodynamically and structurally vulnerable to any severe turbulence they intercept at altitude. Since the stratosphere is very dry and thus has no in situ cloud-related sources of turbulence from severe weather, only clear-air turbulence CAT can occur. Nearly a half-century of accumulated U-2 experience has revealed that, away from deep convective tropical weather, severe turbulence encounters at altitude usually occur near mountains. The only plausible connection between underlying topography and severe in-flight CAT in the middle stratosphere at 20 km is via the direct communication of mountain-generated gravity waves mountain waves from the ground to the stratosphere, where they break and generate turbulence. Thus forecasts of stratospheric mountain wave CAT are required, but current operational numerical weather prediction NWP models cannot provide them. The exception is the NRL Mountain Wave Forecast Model MWFM, first developed in the early 1990s with the specific goal of forecasting stratospheric mountain wave CAT for polar stratospheric science flights with NASAs ER-2. The MWFM has now clocked up over a decades worth of experience and has been continuously maintained and significantly upgraded at NRL over that time the upgrades have both significantly improved the stratospheric CAT forecasts, and yielded new forecast products such as mountain wave-induced cloud formation potential and upper tropospheric mountain wave CAT. Our focus in this paper is to provide a general introductory overview of the MWFM, focusing less on the mathematical details and more on its current status and performance as a relatively mature global forecasting tool for stratospheric mountain wave CAT.
- Atmospheric Physics