The Relationship Between RFD Thermodynamic Deficit and RFGF Vertical Structure in High-Resolution Simulated Supercells

It has been shown that non-tornadic and weakly tornadic supercells are associated with RFDs containing large deficits in equivalent and density potential temperature, while strongly tornadic supercells produce RFDs with much weaker deficits. In a previous work by these authors, an empirical relationship was derived for cold pool slope given ambient shear, cold pool potential temperature deficit, and shear depth using a two-dimensional cold pool model. The results revealed that, in the same sheared flow, the edge of a strong cold pool is less inclined than that of a weaker cold pool. Also, outflow in weak ambient shear has a steeper slope than the same outflow in stronger ambient shear. It is proposed that the relationship between cold pool slope, buoyancy deficit, and ambient shear can be used to gain insight into a supercell’s tornadic potential using remote sensing (e.g., a mobile radar RHI of the RFGF) in place of direct thermodynamic measurements in the RFD, which may be nonexistent or difficult to obtain.

To further assess the relationship between RFGF slope and thermodynamic deficit, three-dimensional cold pools associated with three different high-resolution supercells simulated in CM1 are analyzed. This study aims to identify the heterogeneity of both RFD thermodynamics and low-level vertical wind shear in the inflow, the effects on the slope of the simulated RFGF, and the relationship to the presence of strong low-level vertical vorticity. The results are compared to the empirical equations for cold pool slope formed from our prior two-dimensional cold pool simulations. While these simulated three-dimensional supercell cold pools display a significant amount of heterogeneity, which will be discussed, there is a visible relationship between the vertical structure of the RFGF as seen on Doppler velocity plots and the thermodynamic deficit within the outflow. We pose this relationship can be useful in identifying sharp changes in equivalent and virtual potential temperature across different storms and between various periods of downdraft evolution within a single storm (e.g., such as those associated with RFD surges).