Surface analysis of the rear-flank downdraft in two tornadic supercells

The rear-flank downdraft regions of two tornadic supercells were sampled on 12 June 2004 (near Lehigh, IA) and 9 June 2005 (near Hill City, KS) using mobile mesonet instrumentation platforms as part of Project WIRL (Wheeled Investigation of Rear-flank Downdraft Lifecycles). The data for the former case were collected using a transitional “lifecycle” routine. This technique allowed for a unique dataset that reveals variations in surface equivalent potential temperature, virtual potential temperature, and wind speed and direction with time within the rear flank of this storm. Data for the latter case were obtained using a stationary “snapshot” routine allowing for time-to-space conversions of the rear-flank downdraft within a few kilometers of a tornadic circulation.

In the 12 June 2004 case, the tornadic circulation was accompanied by large equivalent potential temperature deficits within the rear-flank downdraft. The 9 June 2005 sample was highlighted by heavy precipitation near the tornado itself, yet relatively small negative (and even positive) equivalent and virtual potential temperature perturbations. These datasets illustrate the ever changing composition of rear-flank downdraft parcels and how these thermodynamic and kinematic trends with time may relate to the maintenance of the accompanying tornadic activity.