Different El Niño Flavors and Associated Atmospheric Teleconnections as Simulated in a Hybrid Coupled Model

Abstract

A previously developed hybrid coupled model (HCM) is composed of an intermediate tropical Pacific Ocean model and a global atmospheric general circulation model (AGCM), denoted as HCM^AGCM. In this study, different El Niño flavors, namely the Eastern-Pacific (EP) and Central-Pacific (CP) types, and the associated global atmospheric teleconnections are examined in a 1000-yr control simulation of the HCM^AGCM. The HCM^AGCM indicates profoundly different characteristics among EP and CP El Niño events in terms of related oceanic and atmospheric variables in the tropical Pacific, including the amplitude and spatial patterns of sea surface temperature (SST), zonal wind stress, and precipitation anomalies. An SST budget analysis indicates that the thermocline feedback and zonal advective feedback dominantly contribute to the growth of EP and CP El Niño events, respectively. Corresponding to the shifts in the tropical rainfall and deep convection during EP and CP El Niño events, the model also reproduces the differences in the extratropical atmospheric responses during the boreal winter. In particular, the EP El Niño tends to be dominant in exciting a poleward wave train pattern to the Northern Hemisphere, while the CP El Niño tends to preferably produce a wave train similar to the Pacific North American (PNA) pattern. As a result, different climatic impacts exist in North American regions, with a warm-north and cold-south pattern during an EP El Niño and a warm-northeast and cold-southwest pattern during a CP El Niño, respectively. This modeling result highlights the importance of internal natural processes within the tropical Pacific as they relate to the genesis of ENSO diversity because the active ocean–atmosphere coupling is allowed only in the tropical Pacific within the framework of the HCM^AGCM.

摘 要

在前期工作中,我们已将中等复杂程度的热带太平洋海洋模式和全球大气环流模式(AGCM)相互耦合,成功发展了一个混合型耦合模式(HCM),称为HCMAGCM,并可用于海气系统的长期积分试验。本研究基于其1000年的控制试验结果,考察了该模式对东部型(EP)和中部型(CP)El Niño及其全球大气遥相关的模拟情况。分析表明,HCMAGCM能够真实地模拟两类El Niño事件相应的海表温度、风场和降水等变量在强度和纬向位置上的不同特征。进一步,海表温度热收支分析表明,温跃层反馈和纬向平流反馈分别主导了EP和CP El Niño事件的发展。另外,该模式也能够模拟出北半球冬季热带外大气对两类El Niño事件不同的响应特征:EP El Niño倾向于在北半球激发向极地的波列结构,而CP El Niño倾向于产生类似太平洋北美型(PNA)遥相关的波列结构。这种不同的波列响应给北美地区产生了不同的气候影响,EP El Niño期间北美地区为北暖-南冷的响应,而CP El Niño期间表现为东北暖-西南冷的分布特征。由于在HCMAGCM框架下,只允许在热带太平洋区域有海洋和大气的相互耦合,所以,该模式结果强调了热带太平洋内部自然变率过程对产生ENSO多样性及其影响的重要作用。