Sensitivity of simulated vortex development to near-surface temperature perturbations

Colder supercell outflow—generally linked to lower boundary-layer relative humidity—is often detrimental to tornado genesis and maintenance. However, the rear flank is anything but homogeneous; surface temperatures within a single rear-flank downdraft may vary by as much as 10–20 K over just a few kilometers. In this study, we analyze how local variations in supercell outflow and the near-inflow environment might influence tornado genesis and evolution. This is accomplished with a 25-member ensemble of high-resolution idealized simulations, with each member made unique by the addition of a small region of cooler air prior to tornadogenesis. In each simulation, the resulting “blob” of cooler near-surface air advects toward the developing vortex and, in some cases, meaningfully alters the resulting vortex-scale evolution. Regardless of the initial blob location, all of the ensemble members featured a vortex with a weaker peak intensity than the blob-less control run. Blobs inserted in the near inflow exhibited the least impact on tornado genesis and evolution; the blob encountered the rear-flank gust front and was advected away from the low-level updraft. Vortices were meaningfully weaker in simulations with a blob inserted in the forward flank. Although vortex-bound Lagrangian vorticity diagnostics were similar between this run and the control run, the blob resulted in a sub-optimal horizontal separation of the developing vortex from the low-level updraft core. These findings highlight the sensitivity of vortex development to local cooling, perhaps reminiscent of rear-flank internal surges or cold pools from cell mergers in the real atmosphere.