Sedimentation calculations within an Eulerian framework using series of basis functions

Abstract

AbstractA gravitational sedimentation parametrization is presented, which sets the dynamic framework for the parametrization philosophy of linear combination of basis functions. The entire drop spectrum is represented as a linear combination of log‐normal distributions as part of an Eulerian simulation framework, in which all parameters of the distributions are calculated based on a prescribed set of three prognostic moments, thus eliminating the need of fixing any parameter to close the system of equations. The parametrization presents the advantage of avoiding the classification of water substance in artificial categories such as cloud water or rain water. Several experiments were performed, with an increasing number of distribution functions up to three, and with different sets of moments to establish which set performed the best. The comparison against the solution of an explicit sedimentation model shows that this parametrized approach is accurate enough to consider its inclusion in multi‐dimensional cloud models, achieving a better representation of the spectra with the use of a three‐member linear combination of basis functions.