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Wake Vortex Structure and Aerodynamic Origin in Severe Thunderstorms

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  • 1 National Severe Storms Laboratory, Norman, Okla. 73069
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Abstract

The radar and surface structure of a severe thunderstorm's wake vortex on 25 June 1969 are examined. Two probable aerodynamic causes for wake vortex formation are Kármá vortices and starting vortices to the updraft lee. Kármán vortices would form, as do those observed, within the echo core at the updraft lee “edges” and move downstream with the ambient flow. However, in contrast to Kármán theory, radar reflectivity distributions consistently suggest anticyclonic flow. Starting vortices should develop as observed, during transition of a thunderstorm updraft from non-rotational to rotational state, as a vortex of comparable strength but opposite circulation. Four other thunderstorms examined also produced severe weather, increased intensity rapidly, and turned right or formed hook echoes contemporaneously with vortex shedding.

Abstract

The radar and surface structure of a severe thunderstorm's wake vortex on 25 June 1969 are examined. Two probable aerodynamic causes for wake vortex formation are Kármá vortices and starting vortices to the updraft lee. Kármán vortices would form, as do those observed, within the echo core at the updraft lee “edges” and move downstream with the ambient flow. However, in contrast to Kármán theory, radar reflectivity distributions consistently suggest anticyclonic flow. Starting vortices should develop as observed, during transition of a thunderstorm updraft from non-rotational to rotational state, as a vortex of comparable strength but opposite circulation. Four other thunderstorms examined also produced severe weather, increased intensity rapidly, and turned right or formed hook echoes contemporaneously with vortex shedding.

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