What Differentiates Tornadic From Non-Tornadic Tropical Cyclone Supercells?

This study investigates the factors that distinguish tropical cyclone supercells from counterparts in the central plains using Cloud Model 1 (CM1). Grid point soundings from Rapid Refresh (RAP) are examined in the vicinity of tornado-warned cells within TCs making landfall over the continental U.S. (CONUS) from 2013 to 2020. These soundings were averaged into two distinct input profiles: one for cells that were tornado-warned but did not produce a tornado (non-tornadic), and another for cells that generated EF2 or stronger tornadoes (tornadic). These refined soundings were input into CM1 to generate an ensemble of storms for each identified scenario, perturbed by initial random noise. With each of these ensembles, time series for multiple parameters were looked at including surface vorticity, surface wind, updraft area, and cold pool area. The results reveal that following the initial spin-up period, the simulations based on the tornadic sounding had more pronounced vorticity peaks, smaller updrafts, and reduced cold pool areas. Also, multiple severe weather parameters were looked at for each sounding to show tornado potential, including convective available potential energy (CAPE), storm relative helicity (SRH), and shear. Generally, the factors that are used to differentiate tornadic and nontornadic plains supercells are also applicable to TC supercells. Notably, CAPE in the tornadic sounding is approximately 50% higher than in the non-tornadic sounding, SRH is approximately 55% larger, and the 6km shear is over 60% greater, underscoring the significance of shear in TC tornado formation. Sensitivity simulations featuring systematic variations in middle tropospheric relative humidity (RH) show that TC supercells are unable to sustain themselves and succumb to entrainment when the free troposphere is dried but all other factors are held the same. This suggests that a nearly-saturated free troposphere, which minimized the deleterious effects of entrainment, is an essential element to the maintenance of TC supercells.