Prognostic Precipitation, Multi-Scale cloud physics, and Aerosol cloud interactions

Description

We use idealized, single column and global simulations to test the impact of prognostic precipitation on cloud microphysics and precipitation and intercompare microphysics schemes to better understand the scale sensitivity of cloud physics and aerosol-cloud interactions. Warm rain cases compare well across schemes, and prognostic precipitation is shown to respond differently to perturbations of drop number. As expected with prognostic precipitation, accretion is stronger than with diagnostic precipitation and increases with Liquid Water Path (LWP) in cases faster than autoconversion. Global solutions with prognostic precipitation feature slightly thicker clouds for the same set of parameter settings. The new balance of process rates significantly reduces aerosol cloud interactions, both through radiative effects and sensitivity of precipitation. Global radiative effects of anthropogenic aerosol perturbations drop by over 30%. Sub-stepping microphysics yields fewer cases when process rates are limited by numerics, and for multiple sub-steps of cloud macro-physics with the microphysics, reducing aerosol-cloud interactions further. Process rate limiters are still active in mixed phase regimes, indicating that coupling of microphysics to the rest of the global model is strongly affecting the results.