The Predicted Particle Properties (P3) bulk microphysics scheme (Morrison & Milbrandt, 2015) represents a significant advance from traditional bulk schemes, where ice-phase particles are artificially partitioned into several different predefined categories with fixed properties. Ice particle evolution is simulated through the full range of growth processes without predefined ice categories using predicted rimed mass and volume. The rimed particles (graupel/hail) which are important cloud microphysical components in mixed and deep convective clouds are not included in the Gettelman and Morrison (2015; MG2) scheme which is commonly used in climate models such as CESM and E3SM. Recently, the double-moment P3 has been developed into a triple-moment scheme with shape parameters of rain and ice particles predicted by prognosing the 6th moment of Gamma distribution (Paukert et al. 2019; Milbrandt et al. 2021). The added prognostic moment allows the spectral width to vary independently from other size distribution parameters.
The double-moment version of the P3 scheme (single ice category configuration) has been implemented in the E3SMv2 and the performance has been evaluated. Further, we adopted the triple-moment scheme with predicted shape parameters of rain and ice-particles to reduce the excessive size sorting which allows more realistic precipitation mean sizes at lower levels including the surface. This implementation would particularly benefit high-resolution simulations as the community is moving toward global convective-permitting scales.
The model performance is evaluated based on 6 year simulations at 1° and ¼ ° resolution and compared to double-moment P3, MG2, and observations. The evaluation is performed with various observable climatological products like radiation, precipitation, cloud fraction as well as the field measurements of LWC, IWC, rain size distribution and raindrop diameter. The microphysical process rates will be analyzed to understand the impact of the varying rain/ice-particles spectra width. Areas of improved and degraded performances will be highlighted, and future work will be discussed.