Wednesday, 9 November 2016: 4:45 PM
Pavilion Ballroom East (Hilton Portland )
The structure and evolution of the tornado debris signature (TDS) as manifest by the co-polar cross-correlation coefficient (ρhv) are examined over a 30 minute period from 5 minutes prior to genesis, through the mature stage of a violent EF5 tornado that occurred in central Oklahoma on 24 May 2011. Results from three-dimensional analyses as well as two-dimensional raw data suggest that areas of low ρhv were present prior to tornadogenesis and were associated with debris from a previous tornado that was wrapping into the new, strengthening low-level mesocyclone. The appearance of low ρhv collocated with the nascent tornado occurred just prior to the development of a vertically-continuous tornado vortex signature, during a time when rotation was strengthening at the lowest elevation angle (~500 m ARL). In multiple occurrences, the TDS became asymmetric, having at least two different types of spiral bands extending out radially from the primary region of reduced ρhv. It is hypothesized that these bands were associated with debris being ingested into the tornado from narrow channels of inflow in some cases, and debris shedding or accumulation of debris along a secondary rear-flank gust front on the south-side of the TDS in other cases. A well-defined period of debris fallout was also observed as the tornado underwent a weakening trend. The decrease in radial velocities preceded the debris fallout by several minutes.
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