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Caustic Activation of Rain Showers

Phys. Rev. Lett. 97, 048501 – Published 28 July 2006
Michael Wilkinson, Bernhard Mehlig, and Vlad Bezuglyy

Abstract

We show quantitatively how the collision rate of droplets of visible moisture in turbulent air increases very abruptly as the intensity of the turbulence passes a threshold, due to the formation of fold caustics in their velocity field. The formation of caustics is an activated process, in which a measure of the intensity of the turbulence, termed the Stokes number St, is analogous to temperature in a chemical reaction: the rate of collision contains a factor exp(C/St). Our results are relevant to the long-standing problem of explaining the rapid onset of rainfall from convecting clouds. Our theory does not involve spatial clustering of particles.

DOI: http://dx.doi.org/10.1103/PhysRevLett.97.048501

  • Received 7 April 2006
  • Published 28 July 2006

© 2006 The American Physical Society

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Authors & Affiliations

Michael Wilkinson1, Bernhard Mehlig2, and Vlad Bezuglyy1,2

  • 1Faculty of Mathematics and Computing, The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom
  • 2Department of Physics, Göteborg University, 41296 Gothenburg, Sweden

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