The Sensitivity of Simulated Supercell Structure and Intensity to Variations in the Shapes of Environmental Buoyancy and Shear Profiles

Abstract

Convective storm simulations are conducted using varying thermal and wind profile shapes, subject to the constraints of strict conservation of convective available potential energy (CAPE) and hodograph trace. Small and large CAPE regimes and straight and curved hodographs are studied, each with a matrix of systematically varying thermal and wind profile shapes having identical levels of free convection and bulk Richardson numbers favorable to supercell development. Differences in storm intensity and morphology resulting from changes in the profile shapes can be profound, especially in the small CAPE regime, where, for the moderate shears studied here, storms are generally weak except when the buoyancy is concentrated at low levels. In stronger CAPE regimes, less dramatic relative enhancements of storm updraft intensity are found when both the buoyancy and shear are concentrated at low levels. Peak midlevel vertical vorticity correlates roughly with peak updraft speed in the small CAPE regime, but it shows less sensitivity to buoyancy and shear stratification at larger CAPE. Although peak low-level vertical vorticity can be large in either CAPE regime, it is generally larger in the large CAPE regime, where evaporation of rain leads to the formation of stronger surface cold pools, zones of enhanced horizontal shear, and baroclinic production of horizontal vorticity that can be tilted onto the vertical by storm updrafts. The present parameter space study strongly suggests that, while bulk CAPE and shear are important determinants of gross storm morphology and intensity, significant modulation is possible within a given bulk CAPE and shear class by changing only the shapes of the profiles of buoyancy and shear, either alone or in combination.