A Preliminary Analysis of Low-Frequency Gravity Wave, Line-End Vortex, and Environmental Flow Contributions to Rear-to-Front Flow in Observed MCSs

Mesoscale convective systems (MCSs) produce heavy rainfall and damaging winds that can have devastating impacts to communities in their paths. However, the three-dimensional circulations within MCSs and between MCSs and their environments can be poorly represented in numerical model forecasts, in turn limiting the ability to accurately predict MCSs’ longevity, intensity, and hazards. These circulations are at least partially initiated by low-frequency gravity waves, which themselves are the result of vertical variations in diabatic heating along the MCSs’ leading edges and within their stratiform precipitation regions. We hypothesize that the inability of microphysical parameterizations to faithfully simulate the vertical profiles of diabatic heating within MCSs results in incorrect vertical profiles of diabatic heating within MCSs, leading to incorrect representations of low-frequency gravity waves and the three-dimensional circulations – namely the rear-to-front flow within the stratiform precipitation region – that result from them.

As a first step toward testing this hypothesis, this study uses observations collected by two Dept. of Energy Atmospheric System Research-sponsored field campaigns, the Mid-latitude Continental Convective Clouds Experiment (MC3E) and Plains Elevated Convection At Night (PECAN), to identify low-frequency gravity waves in observations and isolate their contributions to MCSs' rear-to-front flow alongside those from line-end vortices and environmental flows using a wind decomposition into the irrotational and non-divergent winds. This presentation will present these wind decompositions, associated radar analyses, and preliminary gravity-wave identifications of selected MCSs observed during MC3E and PECAN.