Weak ENSO Asymmetry Due to Weak Nonlinear Air–Sea Interaction in CMIP5 Climate Models  

作　　者：Yan SUN Fan WANG De-Zheng SUN 

机构地区：[1]Key Laboratory of Ocean Circulation and Waves,Institute of Oceanology,Chinese Academy of Sciences,Qingdao 266071 [2]Laboratory for Ocean Dynamics and Climate,Qingdao National Laboratory for Marine Science and Technology,Qingdao 266071 [3]Cooperative Institute,for Research in Environmental Sciences,University of Colorado,and NOAA/Earth System Research Laboratory/Physical Sciences Division,Boulder,Colorado 80305,USA

出　　处：《Advances in Atmospheric Sciences》2016年第3期352-364,共13页大气科学进展（英文版）

基　　金：supported by the National Basic Research Program of China under the project“Structures,Variability and Climatic Impacts of Ocean Circulation and the Warm Pool in the Tropical Pacific Ocean”(Grant No.2012CB417401);the Strategic Priority Research Program–Climate Change:Carbon Budget and Related Issues,of the Chinese Academy of Sciences(Grant No.XDA05110302);the China Postdoctoral Science Foundation(Grant No.2012M521378);the Large-scale and Climate Dynamics Program of the U.S.National Science Foundation(AGS 0553111 and AGS 0852329);the Office of Global Programs of NOAA

摘　　要：State-of-the-art climate models have long-standing intrinsic biases that limit their simulation and projection capabilities. Significantly weak ENSO asymmetry and weakly nonlinear air-sea interaction over the tropical Pacific was found in CMIP5 （Coupled Model Intercomparison Project, Phase 5） climate models compared with observation. The results suggest that a weak nonlinear air-sea interaction may play a role in the weak ENSO asymmetry. Moreover, a weak nonlinearity in air-sea interaction in the models may be associated with the biases in the mean climate--the cold biases in the equatorial central Pacific. The excessive cold tongue bias pushes the deep convection far west to the western Pacific warm pool region and suppresses its development in the central equatorial Pacific. The deep convection has difficulties in further moving to the eastern equatorial Pacific, especially during extreme El Nifio events, which confines the westerly wind anomaly to the western Pacific. This weakens the eastern Pacific El Nifio events, especially the extreme E1 Nifio events, and thus leads to the weakened ENSO asymmetry in climate models. An accurate mean state structure （especially a realistic cold tongue and deep convection） is critical to reproducing ENSO events in climate models. Our evaluation also revealed that ENSO statistics in CMIP5 climate models are slightly improved compared with those of CMIP3. The weak ENSO asymmetry in CMIP5 is closer to the observation. It is more evident in CMIP5 that strong ENSO activities are usually accompanied by strong ENSO asymmetry, and the diversity of ENSO amplitude is reduced.State-of-the-art climate models have long-standing intrinsic biases that limit their simulation and projection capabilities. Significantly weak ENSO asymmetry and weakly nonlinear air-sea interaction over the tropical Pacific was found in CMIP5 （Coupled Model Intercomparison Project, Phase 5） climate models compared with observation. The results suggest that a weak nonlinear air-sea interaction may play a role in the weak ENSO asymmetry. Moreover, a weak nonlinearity in air-sea interaction in the models may be associated with the biases in the mean climate--the cold biases in the equatorial central Pacific. The excessive cold tongue bias pushes the deep convection far west to the western Pacific warm pool region and suppresses its development in the central equatorial Pacific. The deep convection has difficulties in further moving to the eastern equatorial Pacific, especially during extreme El Nifio events, which confines the westerly wind anomaly to the western Pacific. This weakens the eastern Pacific El Nifio events, especially the extreme E1 Nifio events, and thus leads to the weakened ENSO asymmetry in climate models. An accurate mean state structure （especially a realistic cold tongue and deep convection） is critical to reproducing ENSO events in climate models. Our evaluation also revealed that ENSO statistics in CMIP5 climate models are slightly improved compared with those of CMIP3. The weak ENSO asymmetry in CMIP5 is closer to the observation. It is more evident in CMIP5 that strong ENSO activities are usually accompanied by strong ENSO asymmetry, and the diversity of ENSO amplitude is reduced.

关 键 词：ENSO asymmetry NONLINEARITY air-sea interaction cold tongue CMIP5 deep convection 

分 类 号：P732[天文地球—海洋科学] P732.6