HR: 10:30h
AN: A42A-01 INVITED     [Abstracts]
TI: A New Multi-moment Microphysics Scheme
AU: * Yau, P M
EM: peter.yau@mcgill.ca
AF: McGill University, Dept. of Atmospheric & Oceanic Sciences, 805 Sherbrooke St. West, Montreal, QC H3A2K6 Canada
AB: Microphysical processes affect directly the formation and distribution of precipitation. In numerical models, these processes are parameterized. In bulk schemes, the size spectrum of each hydrometeor category is often described by a three-parameter gamma distribution function. Two-moment schemes generally treat the intercept and slope as prognostic parameters while holding the dispersion parameter alpha constant. We investigated the role of alpha and its effects on sedimentation and microphysical growth rates. It is found that the size-sorting mechanism, which exists in a bulk scheme when different fall velocities are applied to advect the different predicted moments, is significantly different depending on whether a single-momnet, two-moment, or three-moment formulation is used. In addition, the instantaneous hydrometeor growth rates are also changes with the dispersion parameter. Motivated by these results, a new mixed-phase microphysics scheme, with complexity ranging from a one-moment version to a three-moment version, has been developed. Experiments on precipitation development in the context of a kinematic updraft were carried out. It is shown that the three-moment version demonstrates superior performance in terms of the vertical distribution of the hydrometeor mass content and surface precipitation rate.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
SC: Atmospheric Sciences [A]
MN: 2005 Joint Assembly