9.5 Evolution of angular momentum within observed tornadic mesocyclones

Wednesday, 5 November 2014: 10:00 AM
Madison Ballroom (Madison Concourse Hotel)
James Marquis, Pennsylvania State University, University Park, PA; and P. Markowski, Y. Richardson, J. Wurman, and K. Kosiba

The evolution of angular momentum within the low-level mesocyclones of observed tornadic supercell storms is evaluated using a combination of high-resolution dual-Doppler wind syntheses (~100 m horizontal grid spacing) and storm-scale ensemble model analyses (500 m horizontal grid spacing) produced by assimilating mobile radar observations with the ensemble Kalman filter. Changes in the vertical and horizontal angular momentum fluxes through cylindrical volumes encompassing the low-level circulation are related to the evolution of rear-flank downdraft surges and the density of the outflow comprising each mesocyclone (for those storms in which observations or model analyses are available). Net changes in near-surface angular momentum within cylindrical volumes of varying radii (intended to represent differing spatial scales) are compared to the evolution of tornado intensity measured using near-surface unsmoothed radial velocity observations to determine the response of the tornado to changes in the larger-scale circulation, updrafts, and downdrafts surrounding it. Results are compared among the sample of supercells, which encompasses a variety of tornadoes of various intensity and duration, to determine which processes concentrating angular momentum the mesocyclones result in differing tornado intensities and life times.
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