Jana B. Houser, Howard B. Bluestein, and Jeffrey C. Snyder
There is increasing evidence that the behavior of some tornadoes forming from mesocyclones is not consistent with the dynamic pipe effect (DPE), also known as the top-down theory (Alexander 2010, French et al. 2013, 2014, Houser 2013). Rather, the results from these studies suggest that at least some mesocyclonic tornadoes form nearly simultaneously or perhaps from the bottom up over the lowest several km of the troposphere. This study aims to further test the hypothesis that tornadoes form very rapidly and do not conform to the spatiotemporal tendency proposed by the DPE by broadening the number of cases analyzed. It expands the investigation of the evolution of rotation immediately prior to and during tornadogenesis (or a time when tornadogenesis appears imminent) by examining a variety of additional case studies of tornadoes with varying intensity, and a null case. Observations from a rapid-scan, X-band, polarimetric, Doppler radar (RaXPol) spanning several seasons of the University of Oklahoma's spring field project are used to track the Doppler velocity couplet associated with strong rotation (either a nascent tornado, or a failed tornado) over time and height for five events: 1) a violent tornado (EF-5) that occurred on 24 May 2011 near El Reno, Oklahoma; 2) a weak tornado that occurred on 18 March 2012 in southwestern Oklahoma; 3) a second weak tornado that occurred on 29 May 2012 in central Oklahoma, 4) a subtornadic vortex that occurred on 27 May 2013 in central Kansas, and 5) a nontornadic but severe supercell with strong low-level rotation that occurred in SW OK on 23 May 2011. Comparisons will be made between the spatiotemporal evolution of inbound-outbound velocity couplets for the five cases in order to determine the degree of consistency observed during the different cases of tornadogenesis (or tornadogenesis failure).
Alexander, C. A 2010: A mobile radar based climatology of supercell tornado structure and dynamics. Ph.D. Dissertation, University of Oklahoma, Norman, OK 229 pp.
French, M. M., H. B. Bluestein, I. Popstefanija, C. A. Baldi, and R. T. Bluth, 2013: Reexamining the vertical development of tornadic vortex signatures in supercells. Mon. Wea. Rev., 141, 4576-4601.
_____, _____, _____, _____, _____, 2014: Mobile, phased-array, Doppler radar observations of tornadoes at X-band. Mon. Wea. Rev., 142, 1010-1036.
Houser, J. B. 2013: Observations of supercell tornado evolution using a mobile, rapid-scan, Doppler radar. Ph.D. Dissertation, University of Oklahoma, Norman, OK, 264 pp.