Eastern equatorial Pacific SST seasonal cycle in global climate models: from CMIP5 to CMIP6
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Eastern equatorial Pacific SST seasonal cycle in global climate models: from CMIP5 to CMIP6 Zhenya Song1, 2, Hailong Liu3, Xingrong Chen4* 1 First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China 2 Laboratory for Regional Oceanography and Numerical Modeling, Pilot National Laboratory for Marine Science and
Technology (Qingdao), Qingdao 266237, China 3 School of Oceanography, Shanghai Jiaotong University, Shanghai 200240, China 4 National Marine Environmental Forecasting Center, Ministry of Natural Resources, Beijing 100081, China
Received 15 August 2019; accepted 27 September 2019 © Chinese Society for Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract
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. Key words: CMIP5, CMIP6, eastern equatorial Pacific, SST seasonal cycle Citation: Song Zhenya, Liu Hailong, Chen Xingrong. 2020. Eastern equatorial Pacific SST seasonal cycle in global climate models: from CMIP5 to CMIP6. Acta Oceanologica Sinica, 39(7): 50–60, doi: 10.1007/s13131-020-1623-z
1 Introduction The sea surface temperature (SST) seasonal cycle in the eastern equatorial Pacific (EEP) plays
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