P13A.1 DOW-based dynamic climatology of tornaodes

Thursday, 9 August 2007
Halls C & D (Cairns Convention Center)
Curtis R. Alexander, Center for Severe Weather Research, Boulder, CO; and J. Wurman

Efforts to collect mobile radar observations of tornadoes from the Doppler On Wheels (DOWs) over the past decade during both the VORTEX and ROTATE field projects have yielded a large dataset covering about 100 tornadoes with observed Doppler velocities as high as 135 m s-1. Typical resolution in tornadoes from this dataset is on the order of 50 m X 50 m X 50 m (sometimes as fine as 12 m x 3 m x 3 m) with 30 to 60 s updates and observations usually extending below 100 m AGL and up to 3-5 km AGL. Therefore, it is now possible to construct a tornado climatology based upon high resolution radar observations of actual tornado structure, rather than based on cruder measures of tornado intensity only near damaged structures at the ground. Although this analysis is limited necessarily to the 100 observed cases, it avoids the biases and limitations of damage-only based statistics. Statistical distributions of various tornado structural metrics such as peak ground-relative velocity, vertical vorticity, circulation, angular momentum and core diameter are presented with some preliminary results indicating a preferred size and intensity for supercell tornadoes. A comparison with the damage-based tornado intensity distribution is also shown.
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