Idealized study of the role of stability and shear on mesoscale gravity waves generated by evaporative cooling

Mesoscale Gravity Waves (MGWs) are frequently observed in association with cold pools generated by Mesoscale Convective Systems (MCSs) in summer or warm frontal stable layers behind elevated convection in winter. MGWs can be associated with damaging winds, moderate to heavy precipitation, and occasional heat bursts at the surface. This study examines the role of evaporative cooling on MGW development and structure. Evaporative cooling above the inversion was represented in the model by imposing a cold thermal in the mid troposphere and allowing it to descend and impact the inversion. Simulations using idealized soundings were conducted using the Weather Research and Forecasting model version 3.2.1. 252 simulations were conducted, in which the temperature deficit in the cold thermal, the strength and depth of the surface-based inversion and the amount of ambient vertical wind shear were varied.

The analyses quantify the nature of the wave response to evaporative cooling, and show that shallow, weak surface layers coupled with deep, neutral layers above, favor the formation of waves of elevation. Conversely, deep, strong surface layers coupled with deep, neutral layers above favor the formation of waves of depression. Under certain conditions, the model produced substantial surface heat bursts. This study demonstrates that MGWs can develop as the direct result of evaporative cooling aloft, a common feature within the trailing stratiform region of MCSs and in the wake of elevated convection occurring over warm fronts.