10.3 The Regulation of Tornado Intensity by Updraft Characteristics. Part II: Idealized Simulations

Wednesday, 9 November 2016: 10:45 AM
Pavilion Ballroom (Hilton Portland )
Geoffrey Marion, University of Illinois, Urbana, Illinois; and R. Trapp and S. Nesbitt

Strong-to-violent tornadoes cause a disproportionate amount of damage, in part because both the width and length of a tornado damage track are correlated to tornado intensity (EF scale).  Although examples of intense, narrow-width tornadoes can be found in the observational record, as can examples of weak, large-width tornadoes, the tendency expressed in Brooks (2004) is that the most intense tornadoes are typically the widest.

Herein we explore the simple hypothesis that wider and thus more intense tornadoes should form out of wider rotating updrafts.  The theoretical analysis presented in Part I applies strictly to a rotating updraft within the middle altitudes of the storm (nominally 3 - 7 km AGL), which may not always reflect processes in the tornado-bearing low altitudes of the storm. In Part II, we test the generality of this theoretical analysis using the full nonlinear equations within the context of idealized numerical simulations of supercellular thunderstorms.  Three sets of experiments are conducted using Cloud Model 1 (CM1), wherein the environmental CAPE (and LCL/LFC height), vertical wind shear, and magnitude of the initial forcing are varied.  Correlations between middle-altitude updraft size and low-level vertical vorticity throughout these simulations support this hypothesis.

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