Improvement of the simulation of the summer East Asian westerly jet from CMIP5 to CMIP6

ABSTRACT

The East Asian westerly jet (EAJ) plays a crucial role in affecting the East Asian summer rainfall (EASR). Therefore, evaluations of EAJ simulations are vital for improving the understanding and projections of climate change in East Asia. This study evaluates the simulations of the climatology and interannual variability in the present-day summer EAJ in the CMIP6 models and compares the results with those in the CMIP5 models by analyzing the historical climate simulations of 29 CMIP5 models and 21 CMIP6 models during the period from 1986–2005. In general, the CMIP6 models capture the EAJ more realistically than the CMIP5 models. The results show that the CMIP6 models reasonably capture the spatial features of the climatological zonal wind at 200 hPa and simulate a smaller zonal wind bias along the EAJ. The locations of the EAJ’s core are at the observed location in nearly all CMIP6 models but in only approximately two-thirds of the CMIP5 models. The EAJ’s intensity is closer to the observed value and exhibits a smaller intermodel dispersion in the CMIP6 models. The CMIP6 models also show an improved ability to reproduce the interannual variability in the EAJ’s meridional displacement and have a stronger relationship with the EASR.

Graphical Abstract

摘要

东亚高空西风急流 (简称急流) 对东亚夏季降水有着重要影响, 因此, 评估气候系统模式对急流的模拟能力对理解东亚气候变化至关重要。本文利用21个CMIP6气候系统模式历史气候模拟试验数据, 结合NCEP和GPCP再分析资料, 评估了CMIP6模式对现代 (1986–2005年) 急流气候态和年际变率的模拟能力, 并与CMIP5模式模拟结果进行了对比。结果表明, CMIP6模式模拟的200 hPa纬向风的空间分布特征更加真实, 沿急流方向的偏差更小。在CMIP6模式中, 急流中心位置几乎与观测一致, 但只有约三分之二的CMIP5模式能模拟出急流中心位置。CMIP6模式模拟的急流强度也更接近于观测值, 并且模式间不确定性减小。另外, CMIP6模式也改进了对急流经向位移年际变率的模拟能力, 因而模拟的急流与东亚夏季降水的相关关系更强。总体而言, 相对于CMIP5模式, CMIP6模式明显改进了对急流的模拟效果。

KEYWORDS:

• CMIP6
• model evaluation
• East Asian westerly jet
• East Asian summer rainfall

关键词:

• CMIP6
• 模拟能力评估
• 东亚夏季西风急流
• 东亚夏季降水

Acknowledgments

We acknowledge the World Climate Research Programme, which, through its Working Group on Coupled Modelling, coordinated and promoted CMIP6. We thank the climate modeling groups for producing and making available their model output, the Earth System Grid Federation (ESGF) for archiving the data and providing access, and the multiple funding agencies that support CMIP6 and ESGF.

Disclosure Statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research was supported by the National Key R&D Program of China [grant number 2017YFA0603802], the Strategic Priority Research Program of the Chinese Academy of Sciences [grant number XDA2006040102], and the National Natural Science Foundation of China [grant number 41675084].