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A Case Study of a Large-Amplitude Inertia–Gravity Wave over the Southeast

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Thursday, 27 January 2011
A Case Study of a Large-Amplitude Inertia–Gravity Wave over the Southeast
James H. Ruppert Jr., Colorado State University, Fort Collins, CO; and L. Bosart

Previous research has shown that the passage of large-amplitude inertia-gravity waves (IGWs) can exert significant impacts on sensible weather and be associated with severe turbulence. Examples of sensible weather effects associated with IGW passages include the abrupt cessation of precipitation, large variations in sea level pressure (SLP), and significant wind shifts accompanied by damaging wind gusts, the latter of which can pose a major threat to aviation. The purpose of this analysis is to provide an overview of the environment that favors large-amplitude IGW genesis, organization, and maintenance, show the results of an analysis of a large-amplitude IGW event that occurred on 7 March 2008 over the inland Southeast, and compare and contrast this case with previously published cases.

Surface observations, operational Doppler radar data, and satellite imagery all displayed the signatures of large-amplitude IGW activity in the Southeast on 7 March 2008. IGW passage was accompanied by maximum crest-to-trough surface pressure falls of 10 hPa (30 min)-1 with vector wind shift of 20 m s-1, a sharp back edge to the precipitation shield in radar imagery, and cloud desiccation in satellite imagery. The observed IGW activity appeared to originate in southern Texas near the Rio Grande Valley in association with appreciable upper-level geostrophic imbalance. As the IGW amplified and propagated northeastward at an estimated 26 m s-1, the wave front developed a “sawtooth” pattern, possibly indicative of spatially variable ducting ability, and peaked in amplitude over parts of Mississippi, Alabama, and Tennessee. Though IGW genesis appeared to occur devoid of convection, amplification appeared to be favored along a sharp back edge to the precipitation shield and in the presence of a low-level stable layer that was situated above a surface-based layer of rain-cooled air.