Evaluation of the performance of CMIP5 and CMIP6 models in simulating the South Pacific Quadrupole–ENSO relationship

ABSTRACT The South Pacific Quadrupole (SPQ) is the extratropical South Pacific's second principal sea surface temperature mode. Previous observational studies have shown that the SPQ promotes the onset of the El Nino–Southern Oscillation (ENSO). The present study evaluates and compares simulations of the SPQ–ENSO relationship by 20 climate models from CMIP6 and their corresponding 20 previous models from CMIP5. It is found that 16 of the 20 pairs of models are able to consistently reproduce the spatial pattern of the SPQ. In terms of simulating the SPQ–ENSO relationship, 9 of the 16 CMIP6 models show significant improvement over their previous CMIP5 models. The multi-model ensemble (MME) of these 16 CMIP6 models simulates the SPQ–ENSO connection more realistically than the CMIP5 MME. Further analysis shows that the performance of the model simulations in reproducing the SPQ–ENSO relationship is strongly dependent on their ability to simulate the SPQ-related surface air–sea coupling processes over the southwestern and southeastern South Pacific, as well as the response of the SPQ-related equatorial subsurface ocean temperature anomalies. The improvement of the CMIP6 models in simulating these two processes is responsible for the improved performance of the CMIP6 models over their CMIP5 counterparts in simulating the SPQ–ENSO relationship. 摘要 先前的观测研究表明, 南太平洋四极子海温模态 (SPQ) 可以有效地作为ENSO的前兆信号.本文利用20个CMIP6模式及其对应的20个先前的CMIP5模式的工业化前气候模拟试验数据, 评估和比较了CMIP6以及CMIP5模式对SPQ与ENSO的关系的模拟能力.结果表明, 大多数CMIP5和CMIP6模式可以合理地模拟SPQ的基本特征.与早期的CMIP5模式相比, CMIP6模式能够更加真实地模拟SPQ与ENSO之间的关系.进一步分析表明, CMIP6模式模拟SPQ与ENSO关系的能力提高, 是因为CMIP6模式能够更好地模拟出在副热带/热带太平洋上与SPQ相关的表面海气热力耦合过程, 以及在赤道太平洋上与SPQ相关的次表层海温的异常相应.