21st Conf. on Severe Local Storms


Observations of the formation of low-level rotation: The 5 June 2001 Sumner County, Kansas storm

David C. Dowell, NCAR, Boulder, CO; and Y. P. Richardson and J. Wurman

On 5 June 2001, two Doppler on Wheels radars scanned a mature thunderstorm in Sumner County, Kansas for a period of 30 min. The storm initially contained weak rotation near the northern flank of a quasi-linear low-level updraft. However, during the period of survey, a new center of rotation developed farther south. As the new low-level mesocyclone intensified, updraft and downdraft structures characteristic of a tornadic supercell developed. A weak tornado formed within the new mesocyclone.

Results of an ongoing analysis of this case would be presented at the conference. To date, the wind field has been synthesized from 7 edited dual-Doppler volumes. The quality of observations in this case is unprecedented by many measures. First, the data coverage within both the storm inflow and outflow regions is excellent. In contrast, in many previously published dual-Doppler analyses of supercells, the mesocyclone was near the edge of the data coverage region because observations could not be obtained within clear air. Second, since the target was within 17 km of both radars during the period of survey, features that are small and/or close to the ground are resolved. In particular, the characteristics of the flow within the lowest 1 km AGL are represented by Doppler measurements at 4 (or more) different elevation angles. Third, the time between consecutive dual-Doppler volume scans is only 70 s. This allows one to analyze the evolution of small-scale storm features with great confidence.

The presentation would focus on the evolution of the 3-D velocity and vorticity structures in the storm. In addition, hypotheses of tornadogenesis and low-level mesocyclogenesis would be tested.

extended abstract  Extended Abstract (1.7M)

Session 12, tornadogenesis
Thursday, 15 August 2002, 8:00 AM-10:00 AM

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