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Finescale Radar Observations of the Dimmitt, Texas (2 June 1995), Tornado

Joshua WurmanSchool of Meteorology, University of Oklahoma, Norman, Oklahoma

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Swarndeep GillDepartment of Atmospheric Sciences, University of Wyoming, Laramie, Wyoming

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Abstract

The mature and dissipating stages of a strong tornado were observed from close range by the prototype Doppler On Wheels mobile radar. Volumetric observations repeated eight times over an 840-s period with resolution volumes at the center of the tornado as low as 61 m × 61 m × 75 m = 2.8 × 105 m3 revealed new details about three-dimensional tornado vortex structure and evolution. Observed structures included a conical debris envelope, a low-reflectivity eye, multiple windfield maxima, and multiple semiconcentric bands of reflectivity surrounding the eye. The three-dimensional structure of the debris and single-Doppler wind field were well characterized, as well as more rapid dissipation of the tornado aloft compared to near the ground. Volumetric measures of tornado strength are introduced. A downdraft exhibiting w ∼ −30 m s−1, indicative of a partial two-cell vortex, was observed only during the earliest radar scans when the tornado was near maximum intensity. Comparisons with simple conceptual models of vortices are presented and asymmetries are described. Possible reasons for the lack of radar-observed surface convergence are discussed. Comparisons between observed winds and damage are presented and a potential Fujita scale is introduced.

Corresponding author address: Dr. Joshua Wurman, University of Oklahoma, 100 E. Boyd, Norman, OK 73019.

Email: jwurman@ou.edu

Abstract

The mature and dissipating stages of a strong tornado were observed from close range by the prototype Doppler On Wheels mobile radar. Volumetric observations repeated eight times over an 840-s period with resolution volumes at the center of the tornado as low as 61 m × 61 m × 75 m = 2.8 × 105 m3 revealed new details about three-dimensional tornado vortex structure and evolution. Observed structures included a conical debris envelope, a low-reflectivity eye, multiple windfield maxima, and multiple semiconcentric bands of reflectivity surrounding the eye. The three-dimensional structure of the debris and single-Doppler wind field were well characterized, as well as more rapid dissipation of the tornado aloft compared to near the ground. Volumetric measures of tornado strength are introduced. A downdraft exhibiting w ∼ −30 m s−1, indicative of a partial two-cell vortex, was observed only during the earliest radar scans when the tornado was near maximum intensity. Comparisons with simple conceptual models of vortices are presented and asymmetries are described. Possible reasons for the lack of radar-observed surface convergence are discussed. Comparisons between observed winds and damage are presented and a potential Fujita scale is introduced.

Corresponding author address: Dr. Joshua Wurman, University of Oklahoma, 100 E. Boyd, Norman, OK 73019.

Email: jwurman@ou.edu

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