Poster Session P9.8 The southwest Ohio minisupercell tornado outbreak of 11 July 2006. Part II: Investigation into rear-flank downdraft formation and its relation to tornadogenesis

Wednesday, 29 October 2008
Madison Ballroom (Hilton DeSoto)
Daniel Hawblitzel, NOAA/NWSFO, Wilmington, OH

Handout (1.8 MB)

WSR-88D data from Wilmington, Ohio is used to investigate storm-scale processes within a tornadic minisupercell which passed within 4 miles of the radar during the 11 July 2006 southwest Ohio tornado outbreak.

Following mesocyclone formation, a distinct velocity notch developed on the southern flank of the mesocyclone throughout a significant depth, which is speculated to be a signature of the rear-flank downdraft (RFD). Another notable feature is a frontward-directed area of enhanced velocity above the velocity notch and mesocyclone. This feature is noted to be similar to those observed in supercells within landfalling tropical systems over North Carolina, as depicted in a separate study. It is speculated that this feature was directly involved with the development of the RFD by creating a positive pressure perturbation above the mesocyclone.

Data also suggests that midlevel horizontal vorticity was tilted into the vertical by the RFD, evidenced by a vorticity couplet beneath the mesocyclone, in close horizontal proximity to the velocity notch aloft. A descending reflectivity core can be seen developing in the immediate vicinity of the vorticity couplet which led to the formation of the hook echo. The cyclonic member of the vorticity couplet intensified and grew downward inside the hook echo. Finally, near-ground vertical vorticity was detected in close proximity to convergence beneath the updraft, immediately prior to the first report of a tornado touchdown. This supports the theory that low-level convergence acting on near-ground vertical vorticity may lead to tornadogenesis.

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