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.

Characteristics of Supercells in the Rainband of Numerically Simulated Cyclone Sidr

“…It is evident from the literature that environmental characteristics, such as strong low-level wind shear, moderate storm-relative environmental helicity (SREH), and moderate to large CAPE, are favorable for the development of supercells in the rainband at the time of landfall or over land (McCaul 1991;McCaul and Weisman 1996;Baker et al 2009). McCaul and Weisman (2001) suggested that the CAPE and shear are important determinants of the morphology and intensity of convective cells. However, studies of the characteristics of cells in the rainbands and their environment over the ocean are still limited.…”

The Influence of Horizontal Environmental Variability on Numerically Simulated Convective Storms. Part I: Variations in Vertical Shear

“…For this reason, considerable effort has been devoted to studying storm initiation and evolution, as well as the environmental factors governing overall storm structure. Observations (e.g., Marwitz 1972a,b,c;Rasmussen and Blanchard 1998;Evans and Doswell 2001;Markowski et al 2003) as well as theoretical studies (e.g., Moncrieff and Green 1972;Davies-Jones 1984;Lilly 1986a,b;Rotunno et al 1988) and numerical simulations (e.g., Klemp and Wilhelmson 1978a,b;Weisman and Klemp 1982, hereafter WK82;Weisman and Klemp 1984;McCaul and Weisman 2001) suggest a relationship between storm type and the vertical buoyancy and shear profiles of the environment. However, nearly all studies consider storms in horizontally homogeneous environments while observed environments can contain significant inhomogeneity.…”

A numerical study of cell merger over Cuba – Part II: sensitivity to environmental conditions

“…This method may be not rigorous to simulate the initiation of convection but due to its simplicity it has been widely used in 3-D numerical simulations of thunderstorm structure (Klemp and Wilhelmson, 1978;Weisman and Klemp, 1984;Rotuno and Klemp, 1985;McCaul and Weisman, 2001) and also in cloud merger studies with satisfactory results (Turpeinen and Yau, 1981;Kogan and Shapiro, 1996;Stalker and Knupp, 2003).…”