Sensitivity of Supercellular Tornado Characteristics to Thermal Cold Pool Variations

Recent studies have explored supercell behaviors, particularly regarding tornado production, associated with certain background environments. This was accomplished by analyzing ensembles of high-resolution, simulated supercells, with each member’s evolution varying slightly due to a) very small differences in the initial homogeneous background environment, b) random variability in boundary-layer eddies, or c) altering the strength of parameterized convection initiation. This study uses a similar approach to examine differences in tornado characteristics (e.g., production, intensity, duration) that occur due to systematic thermal perturbations to the boundary layer near the developing vortex. This is motivated by the observation that, while outflow temperature deficits are generally related to boundary-layer humidity in the background environment, small-scale thermal fluctuations are commonly observed in the cold pool. This study examines the degree to which, in an environment strongly supportive of supercellular tornado production, these fluctuations might or might not influence tornado outcomes.

The control run for this study features an intense supercell that produces multiple tornado-like vortices (on a 100-m horizontal grid, referred to as “tornadoes”) within the 4-h simulation period. The first occurs around t = 2.5 h, and several restarts are performed 10 min prior to tornadogenesis. These restarts feature a cold perturbation (in the lowest few hundred meters AGL) of varying magnitudes at different locations with respect to tornadogenesis. These perturbations subsequently alter characteristics of the inflow to the developing tornado, and ultimately influence its evolution. Comparing these evolutionary paths is the focus of this presentation.