Wednesday, 7 November 2012
Symphony III and Foyer (Loews Vanderbilt Hotel)
A three-dimensional cloud model is used to simulate supercell storms in base state environments with moderate buoyancy and varying magnitudes of speed shear in the lowest kilometer as prescribed by bent hodograph shapes. With weaker base state values of 01 km AGL speed shear, storm-relative inflow cannot balance outflow from the rear flank downdraft, and the gust front propagates ahead of the storm updraft and disrupts the organization of strong low-level rotation. As 01 km AGL speed shear is increased, storm-relative inflow strengthens and the gust front remains aligned with the storm updraft. Near-surface rotation builds at the tip of the hook echo, and convergence enhanced by positive zonal accelerations and the subsequent development of westerly winds behind the gust front concentrates vertical vorticity into a single vortex with tornadic wind speeds. Additional supercells are simulated in environments with equal amounts of base state 01 km AGL shear but with the addition of directional shear in the lowest kilometer. Comparison of these storms reveals that a favorable configuration of rear flank gust front outflow allows supercells in environments characterized by bent hodographs produce slightly stronger rotation next to the surface than supercells in environments characterized by greater hodograph curvature.
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