Land-Ocean Contrast of Precipitation Processes in the E3SM Multiscale Modeling Framework with 2-D vs 3-D Cloud Resolving Configurations

An atmospheric multiscale modeling framework (MMF) replaces conventional parameterizations with an embedded cloud resolving model (CRM) in each grid-column to explicitly represent convection and related processes. The MMF approach has been shown to outperform conventional models in capturing many precipitation processes, especially those related to mesoscale convection. Previous studies demonstrate a further improvement in some aspects of the simulated precipitation with the CRM configured in 3-dimensional (3-D) rather than the classic 2-dimensional (2-D) domain. In this study, we use the the Energy Exascale Earth System Model (E3SM) and compare a pair of MMF simulations with 2-D (2dMMF) and 3-D (3dMMF) CRM configurations to explore how the CRM dimensionality impacts precipitation. Our result shows a better representation of the tropical mean precipitation from 3dMMF, while 2dMMF better captures extreme precipitation. In particular, systematic land-ocean differences in precipitation and cloud associated variables are shown between the two simulations. These differences can be attributed to the co-occurrence of CRM throttling (i.e., suppressed convection in due to smaller CRM domains) and dilution effects (i.e., 3D clouds circulations lead to increased entrainment and lower precipitation efficiency). While the dilution effect impacts most of the tropics, the throttling effect is stronger over the ocean. The regional differences of the two effects reflect differences in convective intensity and environmental factors. Overall, the throttling effect results in more humid low layers in 2dMMF and the dilution effect causes more high clouds with less precipitation efficiency in 3dMMF. As a result, more precipitation is shown in 2dMMF compared to 3dMMF over the ocean regions with stronger convection due to the increase of precipitation in 2dMMF caused by throttling effect and the decrease in precipitation efficiency in 3dMMF caused by dilution effect. On the other hand, the slightly weaker precipitation in 2dMMF over the land can be linked to much weaker throttling effect and regional-varying impact of dilution effect on the precipitation efficiency.