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Department of Atmospheric Science

Tues., Dec. 19, 3:10 pm, EN6085

A new approach to parameterize ice-phase microphysics: The Predicted Particle Properties (P3) schem

Dr. Hugh Morrison

National Center for Atmospheric Research


The representation of cloud and precipitation microphysics continues to be a major source of uncertainty in atmospheric models. Traditionally, microphysics schemes partition ice-phase particles into pre-defined, “fixed” categories with prescribed bulk characteristics (cloud ice, snow, graupel, etc.). This approach, which is used in nearly all existing schemes, is intrinsically restrictive and imposes the need for conversion processes between categories, which are poorly constrained and often unphysical.

There has been a recent shift in the parameterization of ice microphysics towards emphasis on the prediction of bulk hydrometeor properties. As part of this shift, an approach called Predicted Particle Properties (P3) has been recently developed and implemented into the Weather Research and Forecasting model. Ice particle properties are predicted and evolve locally in time and space by prognosing four independent mixing ratio quantities. From these variables, important physical properties that describe the ice hydrometeors at a given point in time and space can be derived. This allows the full range of ice particle types to be represented by a “free” ice-phase category. An overview of the P3 scheme will be given and results from model simulations will be presented. Despite the simplicity of the new scheme, its prediction of ice particle properties produces realistic simulation of meteorological phenomena at a reduced computational cost relative to current schemes. Extension of P3 to include multiple “free” ice categories that can each evolve their own set of predicted properties will also be discussed, addressing inherent limitations in the single category version of P3.

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