Hodograph Curvature and Updraft Intensity in Numerically Modeled Supercells

Abstract

A set of numerical simulations of supercell thunderstorms has been carried out with a range of low-level curvatures in the environmental hodograph and midlevel shears. They cover a range of hodograph ?shape,? as measured by the integrated helicity of the lowest 3 km of the hodograph. The peak updraft occurs in the first hour of the storms and tends to be greater for larger values of environmental helicity. There is also a slight tendency for greater updraft intensity with lesser values of midlevel shear. Significantly, air in the core of the updrafts at midlevels (?5 km) is not the most unstable air at the level. The most buoyant air rises in a region with a downward-directed pressure gradient force, which slows its ascent. Conversely, pressure gradient forces at lower levels (2?3 km) accelerate less buoyant air upward into the core of the midlevel updrafts. The pressure gradient force is larger in the cases with more curvature in the environmental wind than the low-curvature environments. This is consistent with predictions of the pressure gradient force derived from a simple Beltrami flow model of a rotating thunderstorm and a scale analysis.