Supercell Dissipation Observed by VORTEX2 on 9 June 2009 and its Impact on the Understanding of Storm Demise

On 9 June 2009, VORTEX2 targeted a supercell thunderstorm in southcentral Kansas that formed just north of a surface front and exhibited low-level rotation, generating at least one reported tornado. However, an hour after the VORTEX2 armada deployed its various assets, the storm updraft was observed to shrink and completely dissipate. Analysis of the data collected suggests that the supercell's demise was not simply a result of moving into cooler, more stable air, as is commonly suspected in many such scenarios. Near-storm soundings over time revealed an environment with very modest changes in stability but sharp decreases in low-level vertical wind shear and storm-relative helicity. We hypothesize that the impact of the small increases low-level stability was secondary to the impact of the weakening kinematic environment. Decreases in low-level shear and storm-relative helicity can impact storm maintenance through the following avenues: 1) cold-pool shear interactions that affect lifting along the supercell's cold pool; 2) changes to the dynamical lifting associated with the “updraft in shear” effect in low-levels; 3) changes to the rate at which horizontal streamwise vorticity is fluxed into the supecell and tilted into updraft helicity. The degree to which changes in the wind profile alone result in the dissipation of a supercell, and the degree to which these three processes are responsible, cannot easily be distinguished with the observations. Thus, a series of numerical experiments are being developed in order to determine the roles of weakening shear/helicity versus increasing stability. The long range goal of these tests is to further our understanding of the processes behind supercell dissipation. Initial results and their implications will be presented.