Another distinct pattern of tree fall, likely not linked to the underlying topography, may have been associated with a rear-flank downdraft (RFD) internal surge during the tornado’s intensification stage. These damage patterns are hypothesized to be the result of flow acceleration caused by channeling within valleys. Concentrated bands of intense tree fall, collocated with and aligned parallel to the axis of underlying valley channels, extend well beyond the primary damage path. A few distinct tree-fall patterns are identified at various locations along the Tuscaloosa–Birmingham tornado track. Results from these simulations suggest that both tornadoes had strong radial near-surface winds. A computationally efficient method of simulating tree fall is applied that uses a Gumbel distribution of critical tree-falling wind speeds on the basis of the enhanced Fujita scale. Normalized mean patterns of observed tree fall from each tornado’s peak-intensity period are subjectively compared with results from analytical vortex simulations of idealized tornado-induced tree fall to characterize mean properties of the near-surface flow as depicted by the model. In this study, aerial imagery of tornado damage is used to digitize the falling direction of trees (i.e., tree fall) along the Joplin, Missouri, and 27 April 2011 Tuscaloosa–Birmingham, Alabama, tornado tracks.
0 kommentar(er)
