An Analysis of the Contributions of Line-End Vortices and Gravity Waves to Mesoscale Convective System Rear Inflow and Stratiform Region Structure in Numerical Simulations

Authors

Blount, Dillon — University of Wisconsin–Milwaukee
Evans, Clark — University of Wisconsin–Milwaukee
Adams-Selin, Rebecca — Atmospheric and Environmental Research, Inc.
Vagasky, Hannah Cecile — Atmospheric and Environmental Research

Category

Convective clouds, including aerosol interactions

Mesoscale convective systems (MCSs) are important contributors of weather in the central United States, including beneficial rainfall, but these systems can also produce damaging winds and flooding.  Within an MCS, there are circulations that impact the overall strength and longevity of these systems especially the rear-to-front flow. Low-frequency gravity waves and line-end vortices contribute to this rear-to-front flow in an MCS. These gravity waves help initiate this flow, and they are created by the atmosphere’s response to vertical variations in the diabatic heating in the convective and stratiform regions. Longer horizontal propagation of these gravity waves is likely in the stratiform region due to the stable stratification. Model forecasts poorly represent MCS circulations, especially the rear-to-front flow in the stratiform region, due to inaccurate characterizations in parameterizations of the latent heating responsible for initiating the rear-to-front flow. Our hypothesis is these gravity waves are a leading contributor to the rear-to-front flow that varies over time with gravity wave modifications, line-end vortices, and environmental flow.

This study uses numerical simulations of MCSs that occurred during two United States Department of Energy/Atmospheric System Research sponsored field campaigns, Midlatitude Continental Convective Cloud Experiment (MC3E) and Plains Elevated Convection at Night (PECAN), to isolate the contributions of line-end vortices and gravity waves to MCSs' rear-to-front flow. The analysis is conducted on two cases that occurred in the Central Plains on 20 May 2011 during MC3E and in Nebraska on 17 June 2015 during PECAN. These cases are simulated using the Advanced Research version of the Weather Research and Forecasting (WRF) model at convection-allowing and large-eddy–resolving scales. The total rear inflow will be decomposed to assess the individual contributions from the line-end vortex, gravity waves, and the large-scale flow. The model-simulated three-dimensional wind is subject to a vorticity/divergence inversion to quantify the contributions of the MCS line-end vortex contributions to the rear-to-front flow. The gravity waves will be identified using a spectral analysis of vertical velocity, and this identification will allow the changes of the wind field to be assessed before and after the gravity wave’s passage. The large-scale circulation will be assessed using a low-pass filtering method.