Composite supercell environments from VORTEX2

The true nature of supercell-induced near-storm variability has not been well-constrained by observations because there have historically been very few cases in which multiple soundings were launched simultaneously from different storm-relative positions. VORTEX2 was unique in that near-synchronous sounding measurements of the near inflow, far-inflow, forward-flank, and rear-flank sectors were made repeatedly over extended time periods for numerous cases. We have identified 14 cases for which a) at least 10 near-storm soundings were made, and b) the deployment of the sounding teams provided a reasonable depiction of the near-storm environment. These cases included 10 tornadic storms and 4 non-tornadic storms, with a total of 197 near-storm soundings.

In the past, most studies have treated soundings as if they were measurements of the local vertical column. However, given the nominal ascent rate of 4-5 m/s for soundings during VORTEX2, sondes could travel horizontal distances as large as 100 km during the ~45 minutes that it took them to ascend to the tropopause. Here, we actually exploit the true storm-relative positions of the individual sondes in order to add horizontal structure to the analysis. The sounding data have a 1 second interval, and each 1-s measurement from each sounding was treated as an individual observation in the analysis, with its own height and storm-relative location. In order to account for differences in surface elevation among soundings, a vertical coordinate transformation is used. For each supercell, one base state sounding is identified, and every other sounding is converted into perturbations in potential temperature, mixing ratio, and wind components. WSR-88D radar data are then used to identify an updraft-mesocyclone location for each radar volume during the period in which soundings are to be analyzed. These positions were used to assign each 1-s sounding record to a storm-relative position. Finally, the soundings are interpolated to a common grid using the Barnes (1973) analysis technique. The end result is a composite of the near- and far-field environment of VORTEX2 supercells. The data will be described in terms of horizontal plan view maps, grid point vertical profiles, and integrated quantities (CAPE, CIN, storm-relative helicity). The long-range goal is then to subdivide the cases and produce composite analyses for groups of interest, including tornadic vs. non-tornadic supercells, and early-in-life vs. late-in-life supercells. This should advance the VORTEX2 focus of understanding storm-environment interactions.