A Case Study of the Interaction of a Mesoscale Gravity Wave with a Mesoscale Convective System

Abstract

his study documents the high-amplitude mesoscale gravity wave (MGW) event of 7 March 2008 in which two MGWs strongly impacted the sensible weather over a large portion of the Southeast United States. These MGWs exhibited starkly contrasting character despite propagating within similar environments. The primary (i.e., long lived) MGW was manifest by a solitary wave of depression associated with rapid sinking motion and adiabatic warming, while the secondary (short lived) MGW was manifest by a solitary wave of elevation (?MGWEL?), dominated by rising motion and moist adiabatic cooling. Genesis of the primary MGW occurred as a strong cold front arrived at the foot of Mexico?s high terrain and perturbed the appreciable overriding flow. The resulting gravity wave became ducted in the presence of a low-level frontal stable layer, and caused surface pressure falls up to ~4 hPa. The MGW later amplified as it became coupled with a stratiform precipitation system, which led to its evolution into an intense mesohigh?wake low couplet. This couplet propagated as a ducted MGW attached to a stratiform system for ~12 h thereafter, and induced rapid surface pressure falls of ≥10 hPa (including a fall of 6.7 hPa in 10 min), rapid wind vector changes (e.g., 17 m s?1 in 25 min), and high wind gusts (e.g., 20 m s?1) across several states. MGWEL appeared within the remnants of a squall line, and was manifest by a sharp pressure ridge of ~6 hPa with a narrow embedded rainband following the motion of a surface cold front. MGWEL bore resemblance to previously documented gravity waves formed by density currents propagating through stable environments.