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AGU: Geophysical Research Letters

 

Keywords

  • raindrops fall speeds
  • warm rain processes

Index Terms

  • Atmospheric Processes: Precipitation
  • Atmospheric Processes: Instruments and techniques
  • Atmospheric Composition and Structure: Cloud physics and chemistry

Abstract

Do all raindrops fall at terminal speed?

Guillermo Montero-Martínez

Posgrado en Ciencias de la Tierra, Universidad Nacional Autónoma de México, Circuito de la Investigación Científica, Mexico City, Mexico

Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México, Circuito de la Investigación Científica, Mexico City, Mexico

Alexander B. Kostinski

Department of Physics, Michigan Technological University, Houghton, Michigan, USA

Raymond A. Shaw

Department of Physics, Michigan Technological University, Houghton, Michigan, USA

Fernando García-García

Posgrado en Ciencias de la Tierra, Universidad Nacional Autónoma de México, Circuito de la Investigación Científica, Mexico City, Mexico

Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México, Circuito de la Investigación Científica, Mexico City, Mexico

A unique relation between raindrop size and fall speed v t (D) is assumed throughout atmospheric science. Yet, our speed versus size measurements of millions of drops during natural rainfall events show that many intermediate sized raindrops fall up to an order of magnitude faster than expected. Furthermore, images of drop clusters reveal that these “super-terminal drops” are differently sized fragments of a recent break-up, moving with the speed of the parent drop and relaxing towards v t (D). Additional evidence of the break-up conjecture includes: (i) positive skewness in the distribution of fall speed deviations, (ii) strong size dependence of fall speed deviations and their maximum values and, (iii) preponderance of super-terminal drops in the presence of large raindrops (i.e., during periods of high rainfall rates).

Received 22 December 2008; accepted 11 May 2009; published 13 June 2009.

Citation: Montero-Martínez, G., A. B. Kostinski, R. A. Shaw, and F. García-García (2009), Do all raindrops fall at terminal speed?, Geophys. Res. Lett., 36, L11818, doi:10.1029/2008GL037111.

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