Integrated In Situ, DOW, and damage observations in tornadoes

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Thursday, 8 November 2012: 4:15 PM
Symphony I and II (Loews Vanderbilt Hotel)
Karen A. Kosiba, Center for Severe Weather Research, Boulder, CO; and J. Wurman and P. Robinson

Handout (4.7 MB)

Analyses of the low-level winds in tornadoes will be presented from two unique data sets, 05 June 2009 (Goshen County, WY) and 25 May 2012 (Russell, KS), which reveal periodic temporal variations in velocity, little variation in wind speed with height, and one- and two-celled low-level vortex structures. Also EF ratings, damage incurred and wind speed measurements suggest inconsistencies between how metrics are applied and actual wind measurements.

During the Goshen County, WY tornado, direct observations of the winds inside the tornado were obtained with an instrumented armored vehicle, the Tornado Intercept Vehicle (TIV) and integrated with Ground Based Velocity Track display (GBVTD) analyses constructed from fine-scale mobile Doppler radar (Doppler On Wheels) data to reveal inward and upward spiraling near-surface flow, upward motion near the surface, and an axial downdraft aloft. FFT analysis of the Rapid-Scan DOW observations every 7 s revealed a periodicity in tornado intensity, with amplitude of ~4 m s-1 and peak energy at periods of 66 s and 108 s. This is consistent with long wavelength, upstream-propagating Rossby-type waves slowly revolving about the tornado at 6-10 m s-1, not short wavelength multiple-vortex type phenomena which would complete orbits in ~20 s. Additionally, simultaneous video documentation of damage occurring during the tornado is related to the direct wind observations, which suggest that wind direction and complex failure modes are important in assigning a damage rating.

During the Russell, KS tornado, data taken by the Rapid Scan DOW, DOW7 and an in situ mobile mesonet provide an instantaneous vertical cross-section (7 levels) of winds from 3.5 m AGL to 30 m AGL. Preliminary analysis indicates little dependency of the wind speeds on height. Additionally, two-dimensional dual-Doppler analyses from DOW7 and the Rapid-Scan DOW with an unprecedented 1.6 km baseline and 7-s GBVTD analyses will be presented illustrating the rapid evolution of the low-level wind structure.