High-Resolution In-Situ Verification of Simulated Supercell Cold Pools

Errors in high-resolution numerical simulations of supercell thunderstorms can stem from inaccuracies in initial conditions, parameterizations, and model numerics. Using an ensemble and assimilating mesoscale data into the ensemble can mitigate initial condition and some model bias errors, permitting focus on errors largely attributable to bulk microphysical parameterizations. Inaccuracies in these parameterizations have led typically to an overestimation of cold pool deficits with single-moment microphysical schemes, usually performing worse than two and multiple moment microphysical schemes. These inaccuracies in cold pool size and strength are associated with other errors in baroclinic vorticity production and updraft strength and location.

This ongoing study uses three different microphysical parameterizations to determine which of these popular schemes produce the most realistic cold pools. Data Assimilation Research Testbed (DART) software, using an EnKF technique coupled with the Weather Research and Forecasting (WRF) model, is used to develop a mesoscale background and then scale down to a domain with 1 km horizontal grid spacing. Mobile radar radial velocity data and WSR-88D data are assimilated into this 1 km domain every two minutes.

During the Verification of the Origins of Rotation in Tornadoes Experiment 2 (VORTEX2), up to 24 StickNet probes, in-situ platforms that measure thermodynamic and kinematic properties, were placed in the path of numerous supercell thunderstorms. StickNets were typically in place to sample a significant portion of the forward flank and almost the entirety of the rear flank in these target storms, considering the resolution (1 km – 3 km spacing) of these deployments, these datasets provide a rare opportunity to test the ability of microphysical parameterizations to correctly reproduce a supercell cold pool. This study will contrast the simulated and observed supercell cold pool characteristics for three VORTEX2 cases: 11 June 2009, 10 May 2010, and 18 May 2010. Differences in areal coverage, shape, and magnitude of temperature deficits will be presented.