Single- and Dual-Doppler Analysis of a Tornadic Vortex and Surrounding Storm-Scale Flow in the Crowell, Texas, Supercell of 30 April 2000

Abstract

Fine-resolution single- and dual-Doppler data were collected in the tornadic region of a supercell storm intercepted by two Doppler-on-Wheels radars on 30 April 2000 near Crowell, Texas. Eleven dual-Doppler analyses characterize the 2D and 3D near-surface wind fields associated with a tornado during a 13-min period. An interesting evolution of the low-level rotation is observed. Initially concentric ?tornado? (?500 m wide) and ?tornado?cyclone? (?2 km wide) radar velocity couplets make a transition into a solitary intermediate-sized (?750 m wide) circulation that widens and makes a further transition into a two-celled multiple-vortex structure with an asymmetric distribution of vertical vorticity. The asymmetry and eventual disruption of the multiple-vortex structure may have been partially controlled by locally strong outflow winds that affect the convergence fields in its vicinity. A smaller (?500 m wide) tornado embedded in a broad area of rotation is subsequently observed. The dual-Doppler wind fields are also used to characterize aspects of the storm-scale flow. Locally surging outflow winds result in a double rear-flank gust front structure. The tornado and tornado?cyclone are completely surrounded by outflow at all observation times and air parcels traced within the inflow to the storm rise along the gust front rather than enter the tornado near the ground.