Simulated Relationship between Wintertime ENSO and East Asian Summer Rainfall: From CMIP3 to CMIP6

Abstract

El Niño-Southern Oscillation (ENSO) events have a strong influence on East Asian summer rainfall (EASR). This paper investigates the simulated ENSO-EASR relationship in CMIP6 models and compares the results with those in CMIP3 and CMIP5 models. In general, the CMIP6 models show almost no appreciable progress in representing the ENSO-EASR relationship compared with the CMIP5 models. The correlation coefficients in the CMIP6 models are relatively smaller and exhibit a slightly greater intermodel diversity than those in the CMIP5 models. Three physical processes related to the delayed effect of ENSO on EASR are further analyzed. Results show that, firstly, the relationships between ENSO and the tropical Indian Ocean (TIO) sea surface temperature (SST) in the CMIP6 models are more realistic, stronger, and have less intermodel diversity than those in the CMIP3 and CMIP5 models. Secondly, the teleconnections between the TIO SST and Philippine Sea convection (PSC) in the CMIP6 models are almost the same as those in the CMIP5 models, and stronger than those in the CMIP3 models. Finally, the CMIP3, CMIP5, and CMIP6 models exhibit essentially identical capabilities in representing the PSC-EASR relationship. Almost all the three generations of models underestimate the ENSO-EASR, TIO SST-PSC, and PSC-EASR relationships. Moreover, almost all the CMIP6 models that successfully capture the significant TIO SST-PSC relationship realistically simulate the ENSO-EASR relationship and vice versa, which is, however, not the case in the CMIP5 models.

摘要

前冬ENSO事件对东亚夏季降水(简称EASR)有重要影响。本文研究了第六次国际耦合模式比较计划(简称CMIP6)的全球耦合气候模式对ENSO–EASR关系的模拟能力,并与第三次和第五次国际耦合模式比较计划(简称CMIP3和CMIP5)的模式模拟结果进行了比较。结果表明,从CMIP5到CMIP6,气候模式对ENSO–EASR关系的模拟能力没有明显改进。与CMIP5模式模拟结果相比,CMIP6模式模拟的相关系数偏低,模式间差异较大。本文进而比较了三代CMIP模式模拟ENSO影响EASR物理过程的能力,发现与CMIP3和CMIP5模式相比,CMIP6模式能更加合理地模拟出ENSO影响热带印度洋海表温度变化的物理过程,并且模式间差异较小;其次,CMIP6模式模拟印度洋海表温度与菲律宾海对流遥相关的能力强于CMIP3模式,但与CMIP5模式相当;最后,CMIP3,CMIP5和CMIP6模式模拟菲律宾海对流与EASR关联的能力相当。与观测相比,CMIP3,CMIP5和CMIP6模式模拟的ENSO和EASR,印度洋海表温度和菲律宾海对流,以及菲律宾海对流和EASR的关系偏弱。此外,所有合理地模拟出印度洋海表温度和菲律宾海对流遥相关的CMIP6模式都能较好地模拟出ENSO–EASR关系,反之亦然;而这一现象在CMIP5模式中并不存在。