A Preliminary Analysis of Line-End Vortex Contributions to Rear-to-Front Flow in Observed and Simulated Mesoscale Convective Systems

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 are influenced by them.

To assist in testing this hypothesis, this study examines an observed 20 May 2011 central Plains MCS that occurred during the Dept. of Energy Atmospheric System Research's Mid-latitude Continental Convective Clouds Experiment. Observed multi-Doppler-derived horizontal wind fields are partitioned into the non-divergent (associated with rotation) and irrotational (associated with divergence) wind components associated with the MCSs' line-end vortices. This is accompanied by an analogous partitioning of the horizontal wind fields associated with an Advanced Research Weather Research and Forecasting (WRF-ARW) large-eddy-scale model simulation of this event. This research represents the first step towards assessing all contributions to the rear-to-front flow (e.g., gravity waves and environmental flow) in both observations, where it is difficult to isolate low-frequency gravity waves given observational limitations, and large-eddy-scale model outputs.