Journal Article

Investigating Mechanisms Driving Differences in the Characteristics of Precipitation in the E3SM Multiscale Modeling Framework With 2D Versus 3D Cloud Resolving Model Configurations

Hsu, Wei‐Ching, Hannah, Walter M., Kooperman, Gabriel J.

2025

Overview

In this study, we compare the Energy Exascale Earth Systems Model (E3SM) multiscale modeling framework (MMF) with the cloud resolving model (CRM) configured in two (2dMMF) and three (3dMMF) dimensions. We explore how CRM dimensionality impacts the representation of mean and extreme precipitation characteristics. Our results show that tropical mean precipitation patterns are better represented in 3dMMF compared to observations (Integrated Multi‐satellitE Retrivals for GPM and Global Precipitation Climatology Project One Degree Daily products), while 2dMMF better captures extreme precipitation intensity, with systematic land‐ocean differences in precipitation and cloud‐associated variables. These differences are attributed to the co‐occurrence of CRM throttling (i.e., suppressed convection in due to smaller numbers of CRM columns and domain size) and dilution (i.e., 3‐D cloud circulations with increased entrainment and lower precipitation efficiency) effects. Overall, throttling results in more low‐level humidity in 2dMMF and dilution contributes to more high clouds with less precipitation efficiency in 3dMMF. Since throttling occurs more strongly over the ocean than land, the 3dMMF tends to have less cloud liquid and precipitation over the ocean and more cloud ice and precipitation over land. These results may serve as a guide for choosing the CRM structure to reduce precipitation and cloud‐related biases. Plain Language Summary Global cloud‐resolving models (CRMs) are compulationally prohibitive for climate length simulations, but an alternate approach that embeds independent kilometer‐scale CRMs in each column of a low‐resolution (∼100 km) global grid can permit convection with lower computational expanse. Such an approach allows cloud‐scale motions to be represented in multi‐year global climate simulations, though at the expense of a disconnection between the global model and CRM grids. In this study we compare two different ways of configuring the embedded CRMs: two‐dimensions (2‐D) aligned in north‐south direction versus three‐dimensions (3‐D) including both north‐south and west‐east directions. The results demonstrate a strong land‐ocean contrast in precipitation, cloud properties, and radiation in the difference between the 2‐D and 3‐D CRM simulations. And the differences are generated by the co‐occurrence of a throttling effect associated with a smaller number of CRM columns in 2‐D, which constrains deep convection, and a dilution effect associated with 3‐D cloud circulations, which enhances mixing and reduces precipitation efficiency. While the dilution effect impacts most of the tropics, the throttling effect is more influential over the ocean. This information can be used to inform the best configuration of the CRM approach for simulating precipitation and related processes in a global climate model. Key Points E3SM MMF with a 3‐D CRM reduces mean precipitation pattern biases relative to IMERG, but weakens overall intensity compared to a 2‐D CRM Weaker throttling with dilution effects in 3dMMF result in less low‐level humidity, more high clouds, and lower precipitation efficiency The impacts of dilution and throttling differ over land and ocean, which leads to an overall shift of precipitation toward land in 3dMMF

• Publisher: John Wiley & Sons, Inc,American Geophysical Union (AGU)
• Subject: Atmosphere / Climatology / cloud resolving model / Clouds / Convection / Dilution / E3SM / Efficiency / Entrainment / ENVIRONMENTAL SCIENCES / Extreme weather / Global precipitation / Mean precipitation / Modelling / multiscale modeling framework / Oceans / Precipitation / Precipitation patterns / Rainfall intensity / Satellite observation / Simulation