10.2 The Regulation of Tornado Intensity by Updraft Characteristics. Part I: Theoretical Background and Supporting Observations

Wednesday, 9 November 2016: 10:30 AM
Pavilion Ballroom (Hilton Portland )
Robert Trapp, University of Illinois, Urbana, IL; and G. Marion and S. W. 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.  This hypothesis is based on conservation of angular momentum, which states that the tornado width (and tangential windspeed) should depend directly on the width (and tangential windspeed ) of the mesocyclone, which serves as the tornado’s parent vortex.  Because a mesocyclone is, strictly speaking, a rotating updraft, the mesocyclone width should increase with increasing updraft width.  In Part I, we develop the theoretical background and then use a simple mathematical model to show support for our hypothesis.  Satellite-based observations of overshooting tops lend further support. 

Brooks, H. E., 2004: On the Relationship of Tornado Path Length and Width to Intensity. Wea. Forecast., 19, 310–319, doi:10.1175/1520-0434(2004)019<0310:OTROTP>2.0.CO;2.

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