Retrieved Pressure Field and Its Influence on the Propagation of a Supercell Thunderstorm

Abstract

An analysis of the observed propagation of the Garden City supercell storm based on data collected by an airborne Doppler radar is presented. The environmental wind profile was characterized by a straight hodograph. Wind syntheses were used to retrieve the perturbation pressure fields in order to isolate the important dynamical processes controlling storm movement. The pressure perturbations produced by the linear and nonlinear effects were comparable in magnitude. The rightward bias in storm motion was primarily a result of the forcing produced by the vertical gradients of perturbation pressure. This finding is consistent with the results based on numerical simulations. The vertical gradients of the linear perturbation pressure were important in determining storm motion early in its life cycle; subsequently, the nonlinear effects dominated. A decomposition of the nonlinear forcing into contributions from cyclostrophically balanced flow and nonlinear shear was also presented. This partitioning revealed that both the forcing produced by the mesocyclone and the horizontal shear that was baroclinically produced by the gradient of buoyancy along the flanks of the updraft were important effects to consider.