Lin et al. (2026) Development of CAS-ESM_MMF: improving East Asian summer precipitation simulation with a Multiscale Modeling Framework

Identification

• Journal: Geoscientific model development
• Year: 2026
• Date: 2026-01-09
• Authors: Guangxing Lin, Wei Ming Liao, He Zhang, Wenbin Kou, Xiaojie Guo, Zhenghui Xie, Qiu Yang, Chenglai Wu, Minghua Zhang
• DOI: 10.5194/gmd-19-327-2026

Research Groups

• College of Ocean and Earth Sciences, Xiamen University, Xiamen, China
• International Center for Climate and Environmental Sciences, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
• State Key Laboratory of Earth System Numerical Modeling and Application, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
• College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, China
• Frontiers Science Center for Deep Ocean Multispheres and Earth System (FDOMES) and Key Laboratory of Marine Environmental Science and Ecology (Ministry of Education), Ocean University of China, Qingdao, China
• Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing, China
• School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY, USA

Short Summary

Traditional global climate models exhibit significant biases in simulating East Asian precipitation due to convection parameterization uncertainties. This study implements a Multiscale Modeling Framework (MMF) into the Chinese Academy of Sciences Earth System Model (CAS-ESM), which explicitly resolves convection, substantially improving East Asian summer precipitation simulations, especially when incorporating convective momentum transport (CMT).

Objective

• To document the implementation of the Multiscale Modeling Framework (MMF) within the CAS-ESM framework.
• To evaluate the impact of MMF on the simulation of East Asian precipitation.
• To investigate the role of convective momentum transport (CMT) parameterization in improving the simulation of the seasonal northward migration of the East Asian summer rainband.

Study Configuration

• Spatial Scale: Global climate model (GCM) with a horizontal resolution of approximately 100 km (1° latitude/longitude). Embedded Cloud-Resolving Model (CRM) with 32 horizontal columns and a grid spacing of 4 km. Focus on East Asia, particularly eastern China, with five selected subregions.
• Temporal Scale: Simulations integrated for 7 years (2000-2006), with 6 years (2001-2006) used for analysis. One experiment (CAS-ESMMMFMF) ran for 4 years (2000-2003), with 3 years (2001-2003) for analysis. Analysis of monthly, daily, and hourly precipitation data, and pentad (5-day) mean precipitation.

Methodology and Data

• Models used:
  • CAS-ESM (Chinese Academy of Sciences Earth System Model)
  • CAS-ESM_MMF (MMF version of CAS-ESM, coupling IAP-AGCM4.1 and SAM CRM)
  • IAP-AGCM4.1 (atmospheric component of CAS-ESM)
  • SAM (System for Atmospheric Modeling, a 2D cloud-resolving model)
  • ESMT (Explicit Scalar Momentum Transport scheme for CMT parameterization)
• Data sources:
  • Global Precipitation Measurement (GPM) mission (IMERG Final Run V06B L3) 0.1° monthly, daily, and half-hourly precipitation rate.
  • Global Precipitation Climatology Project (GPCP V2.3) 2.5° monthly precipitation rate.
  • GPCP 1° daily (1dd v1.3) product.
  • ERA5 reanalysis (0.25° fifth-generation ECMWF atmospheric reanalysis) for meteorological variables (wind, geopotential height at 500 hPa).
  • Hadley Centre 1995–2005 climatology for prescribed Sea Surface Temperatures (SSTs).

Main Results

• The CAS-ESM_MMF significantly reduces the wet bias around the Tibetan Plateau and the dry bias over South China and Southeast Asia, which are prominent in the traditional CAS-ESM.
• The MMF version more realistically represents the intensity–frequency characteristics of precipitation, reducing the overestimation of light rain and improving the simulation of heavy rainfall events.
• CAS-ESM_MMF better captures the monthly evolution of precipitation and simulates a more realistic seasonal northward migration of the East Asian rainband, although with an earlier onset and faster, somewhat step-wise progression compared to observations.
• The inclusion of a convective momentum transport (CMT) parameterization (ESMT scheme) in CAS-ESMMMFMF leads to a smoother northward migration of the rainband and a more accurate simulation of the Western Pacific Subtropical High (WPSH) by suppressing excessive convection over the western Pacific.
• CMT reduces overall precipitation rates in low-latitude regions, alleviating wet biases, likely due to its frictional effects on wind, which reduce low-level convergence.

Contributions

• This study presents the first documentation and comprehensive evaluation of the Multiscale Modeling Framework (MMF) implementation within the CAS-ESM, demonstrating its effectiveness in improving East Asian precipitation simulations.
• It provides a detailed assessment of how MMF enhances the representation of precipitation climatology, annual cycle, intensity–frequency distribution, and the seasonal migration of the East Asian rainband.
• The research uniquely investigates and quantifies the critical role of convective momentum transport (CMT) parameterization within the MMF framework, showing that its inclusion leads to a more realistic simulation of the Western Pacific Subtropical High and a smoother, more accurate northward movement of the East Asian summer rainband, addressing a common limitation in 2D CRM-based MMFs.

Funding

• National Key Research and Development Program for International Scientific and Technological Innovation Cooperation (grant 2022YFE0195900)
• National Natural Science Foundation of China (42275086, 42275173)
• National Large Scientific and Technological Infrastructure “Earth System Numerical Simulation Facility”

Citation

@article{Lin2026Development,
  author = {Lin, Guangxing and Liao, Wei Ming and Lin, Zhaohui and Zhang, He and Kou, Wenbin and Guo, Xiaojie and Xie, Zhenghui and Yang, Qiu and Wu, Chenglai and Zhang, Minghua},
  title = {Development of CAS-ESM_MMF: improving East Asian summer precipitation simulation with a Multiscale Modeling Framework},
  journal = {Geoscientific model development},
  year = {2026},
  doi = {10.5194/gmd-19-327-2026},
  url = {https://doi.org/10.5194/gmd-19-327-2026}
}