The Beijing Climate Center Climate System Model (BCC-CSM): the main progress from CMIP5 to CMIP6

Tongwen Wu ,Fang Wu ,Li Zhang ,Yiming Liu ,Jie Zhang ,Xiaoge Xin ,Yanwu Zhang ,Xueli Shi ,Zaizhi Wang ,Weiping Li ,Yaocun Zhang ,Yongjie Fang ,Min Chu ,Min Wang ,Yixiong Lu ,Fang Zhang ,Jianglong Li ,Laurent Li ,Jie Wei ,Liu Xiang-Wen ,Anning Huang ,Xiaohong Liu

doi:10.5194/gmd-12-1573-2019

Abstract

Abstract. The main advancements of the Beijing Climate Center (BCC) climate system model from phase 5 of the Coupled Model Intercomparison Project (CMIP5) to phase 6 (CMIP6) are presented, in terms of physical parameterizations and model performance. BCC-CSM1.1 and BCC-CSM1.1m are the two models involved in CMIP5, whereas BCC-CSM2-MR, BCC-CSM2-HR, and BCC-ESM1.0 are the three models configured for CMIP6. Historical simulations from 1851 to 2014 from BCC-CSM2-MR (CMIP6) and from 1851 to 2005 from BCC-CSM1.1m (CMIP5) are used for models assessment. The evaluation matrices include the following: (a) the energy budget at top-of-atmosphere; (b) surface air temperature, precipitation, and atmospheric circulation for the global and East Asia regions; (c) the sea surface temperature (SST) in the tropical Pacific; (d) sea-ice extent and thickness and Atlantic Meridional Overturning Circulation (AMOC); and (e) climate variations at different timescales, such as the global warming trend in the 20th century, the stratospheric quasi-biennial oscillation (QBO), the Madden–Julian Oscillation (MJO), and the diurnal cycle of precipitation. Compared with BCC-CSM1.1m, BCC-CSM2-MR shows significant improvements in many aspects including the tropospheric air temperature and circulation at global and regional scales in East Asia and climate variability at different timescales, such as the QBO, the MJO, the diurnal cycle of precipitation, interannual variations of SST in the equatorial Pacific, and the long-term trend of surface air temperature.

Highlights

Changes in global climate and environment are the main challenges that human societies are facing with respect to sustainable development
This paper presents the main advancements of the Beijing Climate Center (BCC) climate system models from CMIP5 to CMIP6 and focuses on the description of the CMIP6 version BCC-CSM2-MR and the CMIP5 version BCC-CSM1.1m, especially with respect to the model physics
Main updates to the model physics include a modification of the deep convection parameterization, a new scheme for the cloud fraction, indirect effects of aerosols through clouds and precipitation, and the gravity wave drag generated by deep convection

Summary

Introduction

Changes in global climate and environment are the main challenges that human societies are facing with respect to sustainable development. Climate and environmental changes are often the consequence of the combined effects of anthropogenic influences and complex interactions among the atmosphere, hydrosphere, lithosphere, cryosphere, and biosphere of the Earth system. To better understand the behaviors of Earth’s climate, and to predict its future evolution, appropriate new concepts and relevant methodologies need to be proposed and developed. Climate system models are effective tools to simulate the interactions and feedbacks in an objective manner, and to explore their impacts on climate and climate change. The Coupled Model Intercomparison Project (CMIP), organized under the auspices of the World Climate Research Programme’s (WCRP) Working Group on Coupled Modelling (WGCM), started 20 years ago as a comparison of a handful of early global coupled climate models (Meehl et al, 1997). More than 30 models participated in phase 5 of CMIP (CMIP5, Taylor et al, 2012) and created an unprecedented dynamic in the scientific commu-

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