| dc.description.abstract | Supercell thunderstorms are simulated using a numerical model in order to probe the effects of changing low-level moisture, and thus lifting condensation level (LCL), on outflow characteristics and the evolution of near-surface rotation. A set of three thermodynamic profiles corresponding to different LCLs are tested with varying low-level shear orientations.
The thermodynamic properties of the simulations are sensitive to variations in LCL, with higher LCLs contributing to broader, more negatively buoyant cold pools. These outflow characteristics exhibit a distinct influence on the positioning of near-surface rotation relative to the mid-level mesocyclone. As LCL increases and outflow becomes more negatively buoyant, there is more forward propagation of near-surface circulation relative to the mesocyclone aloft. It is shown that there is a negative, statistically significant lag correlation between the separation of these mid- and low-level circulations and subsequent production of near-surface vertical vorticity, suggesting that the collocation of these circulations affects the convergence and stretching of circulation-rich air near the surface. The degree to which the overlap of mid- and low-level circulations intensifies preexisting near-surface vertical vorticity depends on a number of interrelated factors, including the low-level storm-relative wind profile and the availability of surface rotation for stretching. That said, these simulations suggest that such an alignment is a necessary prerequisite for the strengthening of near-surface vertical vorticity to occur. Thus, for a given low-level shear orientation, LCL can influence whether appreciable near-surface vertical vorticity is able to form within the storm. | en |
