8.4
Preliminary investigation of tornadogenesis within quasi-linear convective systems
R. Jeffrey Trapp, NOAA/NSSL, Boulder, CO; and M. L. Weisman
A consideration of tornado parent storm types suggests that in quasi-linear convective systems (QLCSs) such as squall lines and bow echoes,the horizontal extent of viable tornado-breeding sites is an order of magnitude larger than in individual supercells. QLCS tornadoes can be strong and produce extensive damage despite "conventional wisdom" that suggests otherwise. Also, QLCS tornadogenesis appears to occur, on average, more rapidly than does supercell tornadogenesis from the perspective of Doppler radar.
These statements serve as our motivation to investigate the formation of tornadoes within quasi-linear convective systems. We do so using a three-dimensional cloud-resolving model. Convection is initiated in a horizontally homogeneous environment using five uniformly spaced thermal perturbations; the environment is characterized by large CAPE and modest unidirectional vertical shear of the horizontal wind.
We will discuss results of a parameter-space study that suggests, for example, that a value of environmental vertical shear greater than 10 m/s over a 2.5 km depth is necessary for the formation of potential tornado-breeding (a classification to be discussed as well) vortices near the ground. We also will present an in-depth analysis of a simulation that exemplifies observed behaviors such as a north-of-apex bias in the near-ground vortex location, and an upscale (in size) growth of the leading-edge vortices. Diagnostic techniques will reveal the mechanism(s) responsible for the generation of these vortices.
Session 8, Tornadoes And Tornadogenesis (Parallel with Joint Session J1)
Wednesday, 13 September 2000, 3:30 PM-4:30 PM
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