The sea surface temperature (SST) seasonal cycle in the eastern equatorial Pacific (EEP) plays an important role in the El Niño-Southern Oscillation (ENSO) phenomenon. However, the reasonable simulation of SST seasonal cycle in the EEP is still a challenge for climate models. In this paper, we evaluated the performance of 17 CMIP6 climate models in simulating the seasonal cycle in the EEP and compared them with 43 CMIP5 climate models. In general, only CESM2 and SAM0-UNICON are able to successfully capture the annual mean SST characteristics, and the results showed that CMIP6 models have no fundamental improvement in the model annual mean bias. For the seasonal cycle, 14 out of 17 climate models are able to represent the major characteristics of the observed SST annual evolution. In spring, 12 models capture the 1–2 months leading the eastern equatorial Pacific region 1 (EP1; 5°S–5°N, 110°–85°W) against the eastern equatorial Pacific region 2 (EP2; 5°S–5°N, 140°–110°W). In autumn, only two models, GISS-E2-G and SAM0-UNICON, correctly show that the EP1 and EP2 SSTs vary in phase. For the CMIP6 MME SST simulation in EP1, both the cold bias along the equator in the warm phase and the warm bias in the cold phase lead to a weaker annual SST cycle in the CGCMs, which is similar to the CMIP5 results. However, both the seasonal cold bias and warm bias are considerably decreased for CMIP6, which leads the annual SST cycle to more closely reflect the observation. For the CMIP6 MME SST simulation in EP2, the amplitude is similar to the observed value due to the quasi-constant cold bias throughout the year, although the cold bias is clearly improved after August compared with CMIP5 models. Overall, although SAM0-UNICON successfully captured the seasonal cycle characteristics in the EEP and the improvement from CMIP5 to CMIP6 in simulating EEP SST is clear, the fundamental climate models simulated biases still exist.

中文翻译：

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全球气候模式中的赤道东太平洋海表温度季节周期：从CMIP5到CMIP6

赤道东太平洋（EEP）的海表温度（SST）季节性周期在厄尔尼诺-南方涛动（ENSO）现象中起重要作用。但是，对EEP中SST季节周期的合理模拟仍然是气候模型的挑战。在本文中，我们评估了17种CMIP6气候模式在模拟EEP中的季节性周期方面的性能，并将其与43种CMIP5气候模式进行了比较。通常，只有CESM2和SAM0-UNICON才能成功捕获年平均SST特征，结果表明CMIP6模型对模型的年平均偏差没有根本改善。在季节性周期中，17种气候模式中的14种能够代表观测到的SST年度演变的主要特征。在春天，12个模型捕获了距赤道东太平洋区域1（EP1; 5°S-5°N，110°–85°W）相对于赤道东太平洋区域2（EP2; 5°S-5°N）的1-2个月，140°–110°W）。在秋天，只有两种型号GISS-E2-G和SAM0-UNICON可以正确显示EP1和EP2 SST的相位不同。对于EP1中的CMIP6 MME SST模拟，在暖期沿赤道的冷偏差和在冷期沿暖的偏差都会导致CGCM的年度SST周期变弱，这与CMIP5的结果相似。但是，CMIP6的季节性冷偏和暖偏均显着降低，这导致年度SST周期更紧密地反映了观测结果。对于EP2中的CMIP6 MME SST模拟，由于全年的准恒定冷偏差，其幅度与观测值相似，尽管与CMIP5模型相比，八月之后的冷偏差明显改善了。总体而言，尽管SAM0-UNICON成功地捕获了EEP中的季节周期特征，并且在模拟EEP SST方面从CMIP5到CMIP6的改进是显而易见的，但基本的气候模型模拟偏差仍然存在。