Articles | Volume 7, issue 2
Geosci. Model Dev., 7, 463–478, 2014
Geosci. Model Dev., 7, 463–478, 2014

Model description paper 04 Mar 2014

Model description paper | 04 Mar 2014

On the analytic approximation of bulk collision rates of non-spherical hydrometeors

A. Seifert1, U. Blahak2, and R. Buhr3,4 A. Seifert et al.
  • 1Hans-Ertel Centre for Weather Research, Deutscher Wetterdienst, Hamburg, Germany
  • 2Deutscher Wetterdienst, Offenbach, Germany
  • 3Universität Hamburg, Hamburg, Germany
  • 4Max Planck Institute for Meteorology, Hamburg, Germany

Abstract. Analytic approximations of the binary collision rates of hydrometeors are derived for use in bulk microphysical parameterizations. Special attention is given to non-spherical hydrometeors like raindrops and snowflakes. The terminal fall velocity of these particles cannot be sufficiently well approximated by power-law relations which are used in most microphysical parameterizations, and therefore an improved formulation is needed. The analytic approximations of the bulk collision rates given in this paper are an alternative to look-up tables and can replace the Wisner approximation, which is used in many atmospheric models.