Cooperative Institute for Research in the Atmosphere

An overview of the P3 property-based bulk microphysics scheme

In 2015, the Predicted Particle Properties (P3) bulk microphysics scheme was introduced.  In the original P3 scheme, all ice-phase hydrometeors were represented by a single “free” category with 4 prognostic variables from which various physical properties could be computed.  As a result, the properties could evolve continuously in time and space and the ice category could represent any type of frozen hydrometeor (within the confines of models that try to represent the complexity of ice particles with simple geometric shapes).  As such, the P3 scheme represented a dramatic shift away from the traditional paradigm of representing ice using pre-defined “typical” categories (e.g. “snow”, “graupel”, etc.) with constant parameters to define their physical properties.  Since its inception, there have been several major developments to P3 that have enhanced its capacity to model ice microphysics. Ice is now triple-moment, it has a prognostic liquid fraction, and has a user-specified number of free categories.

In this presentation, an overview of the P3 scheme and its recent developments will be given along with illustrations of how these advances lead to improved realism of simulations for a wide range of weather.  Limitations and plans for future development will also be discussed.  An argument will be made that in order for the modeling community to advance significantly in its capacity to represent cloud microphysics in both research and operational atmospheric models, the commonly-used traditional approach must be abandoned in favor of property-based microphysics schemes.