Extended Abstract (2.0M)7A.2
Storm structure and decay process of the 9 June, 2009 Greensburg, KS supercell during VORTEX2
Conrad L. Ziegler, NOAA/NSSL, Norman, OK ; and M. I. Biggerstaff, L. J. Wicker, D. W. Burgess, E. R. Mansell, C. M. Schwarz, P. Markowski, Y. P. Richardson, and C. C. Weiss
This study documents the late evolution of the 9-10 June 2009 Greensburg, KS, supercell using VORTEX2 observations, beginning prior to development of an intense low-level mesocyclone and proceeding through the storm's decay phase (~ 2345-0024 UTC). A series of quadruple-Doppler radar analyses (i.e., combining data from the SR1, SR2, and NOXP mobile radars with the Dodge City WSR-88D) provide a storm-scale context to interpret in-situ observations from Mobile Mesonets (MM), StickNets, and mobile soundings of the cold pool, cold outflows, and stratification of the boundary layer (BL) and lower troposphere (LT). The storm was observed to move into colder BL air and a more stable environment as it peaked in overall intensity, before subsequently decaying as an LP storm.
Recent simulations of a right-moving supercell have demonstrated that lateral cold-pool spreading drives an upshear-propagating, right-forward flank boundary that opposes ambient low-level shear and provides BL lifting to help force the continuous redevelopment of the supercell updraft. The latter BL convergence forcing mechanism augments dynamical forcing of vertical motion between the updraft and midlevel mesocyclone, which in turn supports updraft propagation toward the storm's right flank. On the other hand, the Greensburg storm's environment had weakening LT wind shear that might have allowed the outflow to move away from the main updraft sufficiently to weaken the storm. At the same time, the Greensburg storm moved into a colder and more stable, capped BL which may also have contributed to its' weakening.
We will examine the Greensburg storm structure and decay in relation to evolution of the storm's cold pool and environment. The MM and StickNet data will be used to estimate the magnitude of the cold pool temperature deficit in relation to changes of the inflow BL temperature. The mobile soundings document the stratification of the inflow BL, and also provide a rather unique sampling of the storm's cold pool stratification in both the forward-flank downdraft and the trailing storm-scale rear flank downdraft outflows. The radar analyses will document the storm's airflow evolution relative to the cold pool and storm environment. Finally, radar-derived air trajectories will help define the source regions and their evolutions for the forward- and rear flank downdrafts, the low-level mesocyclone, and the main updraft with respect to the overall storm decay.
Session 7A, Supercells and Tornadoes: Supercell Structure and Dynamics I
Tuesday, 12 October 2010, 10:30 AM-12:00 PM, Grand Mesa Ballroom F
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