WRF simulations of a severe squall line: comparison against high-resolution BAMEX observations

Historically, quantitative comparisons between modeled MCSs and observations were limited by spatial and temporal variations between the data sets. Prior research often focused on specific values for internal phenomena to the MCS (e.g. maximum rear-inflow jet wind, cold pool strength, or average storm motions). We will compare the distributions of modeled phenomena to those from recent observations. Using high-resolution multi-sensor data collected during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX 2003) in the trailing stratiform region, transition zone, and immediately behind the convective line, we now have an excellent opportunity to compare modeled versus observed MCS structures. We compared airborne dual-Doppler observations of a BAMEX MCS against high-resolution simulations made with the Weather Research and Forecasting (WRF) model using contoured-frequency-by-altitude diagrams (CFADs) and a new method, contoured-frequency-by-distance diagrams (CFDDs). These diagrams yield bulk statistical comparisons of the vertical and horizontal structure of the observed and modeled system. Each diagram summarizes how frequency distributions vary along a given dimension (height or distance respectively).

We modeled the 10 June 2003 severe squall line. During BAMEX, two airborne Doppler radars scanned this system from the formation of the trailing stratiform region through the decaying phase, providing detailed measurements of radar reflectivity and the three dimensional wind field. Comparisons of CFADs and CFDDs of modeled reflectivity and kinematics to those from airborne dual-Doppler radar syntheses are used to quantify the simulated squall line morphology, rear-inflow jet evolution, and microphysics in this case. The quantitative comparisons made herein are used to classify the robustness of our simulations for future use in modeling studies of MCS structures and rear-inflow jet evolution.