Observed and Numerically Simulated Structure of a Mature Supercell Thunderstorm

Abstract

Through the interactive use of Doppler-radar analyses and a three-dimensional numerical storm simulation the detailed structure of a supercell, tornadic storm is analyzed. This storm, named the Del City storm, occurred in central Oklahoma on 20 May 1977. The storm exhibits certain important features which are essential to maintaining its longevity and which promote the storm's transition to its tornadic phase. These features are strongly influenced by the rotational character of the storm separates the precipitation from the updraft and which orients the resulting downdrafts to which reinforce low-level convergence along the gust front and sustain the storm. Analyses of air parcel and rain trajectories within the storm provide a detailed visualization of this internal structure. These trajectories reveal that. air parcels rising through the cyclonically rotating updraft actually turn anticyclonically with height owing to the influence of the storm relative environmental wind field. Downdraft trajectories suggest that the cold outflow air behind the gust front originates in the environment at heights below 2 km. The distribution of vorticity is also investigated within the mature storm. At low levels the strong cyclonic vorticity is found to be located downwind of the convergence line, along the strong gradient between the updraft and down-draft. The similarities in structure between the observed and simulated storm suggest that the larger scale environment plays a dominant role in structuring many of the detailed features of the storm.