25th Conference on Severe Local Storms

8A.6

Mesocyclone and RFD evolution in simulated supercell storms with varying wind profiles

Matthew S. Van Den Broeke, University of Oklahoma, Norman, OK; and J. M. Straka

In the literature, frequent attempts have been made to understand supercell mesocyclone evolution via observations and modeling. Some such modeling attempts have examined changes produced by varying environmental characteristics, including the wind profile. Most of these attempts have used liquid-phase microphysics. In this research, ice-inclusive microphysics are used with varying hodographs to simulate supercell thunderstorms, and resultant mesocyclone evolution is analyzed. In addition, microphysical variations in the rear-flank downdraft (RFD) are briefly compared.

The three-moment Straka Atmospheric Model (SAM) will be used with a 1s time step and 250m horizontal resolution. The lowest vertical level is 75m above the surface, with increasing vertical grid spacing over 60 vertical levels. Storms are initialized with a warm bubble, and the thermodynamic environment is that of Weisman and Klemp (1982). Two microphysical schemes used include liquid-only and ice-inclusive with nine species of ice-phase hydrometeors. Six half-circle, three full circle, and three -circle wind profiles with varying shear magnitude over the lowest 6 and 10 km serve as input; these are a subset of those examined in Adlerman and Droegemeier (2005). Mesocyclone evolution will be classified as non-cyclic, cyclic occluding, and cyclic non-occluding. Evolution will be compared between liquid-only and ice-inclusive simulations for each wind profile, and between these results and those of Adlerman and Droegemeier. Mesocyclone evolution is shown to be primarily cyclic non-occluding and cyclic occluding. In addition, the role of varying microphysical distributions in the RFD region will be briefly examined, and implications in low-level vertical vorticity distribution explored.

extended abstract  Extended Abstract (1.8M)

wrf recordingRecorded presentation

Session 8A, Supercells and Tornadoes: Downdrafts and Cold Pool
Tuesday, 12 October 2010, 1:30 PM-3:00 PM, Grand Mesa Ballroom F

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