An Idealized Simulation of Quasi-LInear Convective System Mesovortices and Polarimetric Radar Signatures Associated with Mesovortex Genesis

Although there have been numerous studies of polarimetric radar signatures in tornadic supercells, relatively little research has been done to study polarimetric signatures in quasi-linear convective systems (QLCSs). Prior work with tornadic supercells has identified several signatures that are associated with processes that precede tornadogenesis. A decrease in the areal extent or the height of a differential reflectivity (Z_DR) column above the ambient 0°C isotherm indicates weakening of the storm updraft. Changes in the areal extent and magnitude of the Z_DR arc signature indicate variability in the liquid drop size sorting mechanism in the storm inflow. Separation of the Z_DR maximum from the specific differential phase (K_DP) maximum may indicate that storm-relative helicity is locally increasing. The objective of this work is to identify if these or other polarimetric radar signatures may precede QLCS tornadogenesis.

An idealized QLCS was simulated at a horizontal grid spacing of 200 m using the Bryan Cloud Model 1. Three warm bubbles were used to initiate storms in an environment favorable for supercell thunderstorms, which eventually grew upscale into a QLCS. NSSL 2-moment microphysics with hail and graupel large ice classes was used in this simulation. The result was a QLCS with a few areas of strong 2-5 km updraft helicity and several low-level vertical vorticity maxima near the leading edge of the QLCS. Simulated polarimetric radar data has been produced from the model output using the Center for Analysis and Prediction of Storms (CAPS) Polarimetric Radar Simulator. Several processes have been proposed to explain the generation of mesovortices in QLCSs, including solenoidal generation of vorticity within downdrafts that produces a cyclonic mesovortex, and upward or downward tilting of baroclinically generated vorticity along the gust front that produces both a cyclonic and anticyclonic mesovortex. Mesovortices that occurred within the simulation were categorized based on the genesis mechanism, and polarimetric radar signatures were tracked prior to and during the life cycle of each mesovortex. Results of this analysis will be presented.