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.