Session 16.3 The influence of eight basic environmental parameters on the low-level rotation characteristics of simulated convective storms

Friday, 10 November 2006: 9:00 AM
St. Louis AB (Adam's Mark Hotel)
Cody Kirkpatrick, University of Alabama in Huntsville, Huntsville, AL AL; and E. W. McCaul Jr. and C. Cohen

Presentation PDF (400.7 kB)

The low-level vorticity characteristics of simulated storms from a large eight-dimensional parameter space study are examined to determine whether strong near-surface rotation is preferred for certain combinations of environmental parameters. Vorticity histogram profiles are accumulated for each experiment during the second hour of 2 h simulations to assess quantitatively the amounts of cyclonic and anticyclonic vorticity within each of the mature simulated storms. Although the grid mesh features only 500 m horizontal spacing, by itself insufficient to resolve tornadoes explicitly, the findings offer an approach to the problem of identifying which environments are most likely to be able to produce storms that can generate tornadoes. Results demonstrate that low-level cyclonic vorticity equal to or stronger than that at midlevels tends to occur preferentially when LFCs are low and the buoyancy and shear profiles are concentrated at low levels. This signal is particularly strong for cooler, midlatitude temperatures, as opposed to warm, tropical regimes where water loading can hinder updraft intensity. The vorticity amplitudes, both at midlevels and near the surface, are strongly enhanced as convective available potential energy and hodograph effective radius are increased. Although most of the storms that rotate strongly produce roughly equal amounts of cyclonic and anticyclonic vorticity, some of the strongly sheared high-CAPE environments produce storms having a preponderance of cyclonic vorticity when buoyancy profiles are distributed rather than concentrated. The findings from this study could be useful to fine-scale convective modelers seeking to investigate differential environmental propensities for tornadogenesis.

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