EnKF Data Assimilation Experiments of the 18 May 2010 Dumas, Texas Supercell Observed by VORTEX2

A fifteen-minute period of the pretornadic phase of the 18 May 2010 Dumas, Texas supercell was well observed by several platforms participating in the second Verification of the Origin of Rotation in Tornadoes Experiment. Fine-scale dual-Doppler syntheses at Ka-band (TTUKa) combined with high-temporal resolution volumetric single-Doppler data at X-band (MWR-05XP) and in situ observations from a six-probe mobile mesonet reveal the development and decay of a low-level mesocyclone distinct from a persistent midlevel mesocyclone. The low-level mesocyclone develops entirely within the broad-scale rear-flank downdraft (RFD) and exhibits counterrotating vortices originating near the surface and straddling the leading edge of an internal RFD surge gust front. Two additional internal RFD surges develop along the western periphery of the low-level mesocyclone as it intensifies and just prior to its decay.

A summary of observational findings will be presented in tandem with results from ensemble Kalman Filter (EnKF) data assimilation experiments of the Dumas supercell. The EnKF experiments assimilate storm-scale Doppler radar observations at C- (SMART-R) and S-band (KAMA WSR-88D) into an ensemble of 48 members with 500 m horizontal grid spacing. The ability of EnKF analyses to reproduce the rapid evolution of observed small-scale storm features, such as the low-level mesocyclone and internal RFD surges, will be verified through comparison with independent observations from the MWR-05XP and TTUKa platforms. Additionally, quantitative analysis of the origin and forcing mechanisms of the RFD surges and their role in low-level mesocyclogenesis will be presented.