Understanding the Central-Pacific El Nino-Southern Oscillation

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This project considers El Nino/Southern Oscillation (ENSO) which occur in the Central Equatorial Pacific (CP). CP ENSO events are distinct from the canonical ENSO events which occur in the Eastern Equatorial Pacific (EP) and appear as a narrow tongue of sea surface temperature (SST) anomalies extending along the equatorial cold tongue from the South American coast. In contrast, SST anomalies for CP ENSO events extend poleward and eastward from the CP to the subtropical coasts of North and South America, with stronger extension in the Northern Hemisphere. Furthermore, the evolution of EP ENSO events is associated with propagation or basin-wide fluctuation of subsurface ocean temperature anomalies at thermocline depth, while CP ENSO events have subsurface temperature anomalies which develop in situ, without propagation. The PIs note that CP ENSO events have become more common since the 1990s, and recent studies suggest that global warming may lead to further enhancement in CP over EP ENSO activity. They also note that the CP ENSO has received less attention in the literature than the EP ENSO, and studies of ENSO and its connections to the extratropics, including both extratropical precursors and extratropical impacts, have not considered the two ENSO types separately. The project addresses three scientific issues related to CP ENSO events. First, research addresses the underlying dynamics of CP events, and the relationship between CP and EP ENSO dynamics, through the use of idealized models and models of intermediate complexity. Second, the project addresses the role of extratropical forcing in generating CP ENSO events, based on earlier research which identified precursor patterns in sea surface temperatures in the Northern Hemisphere subtropics. Third, the research considers differences in the global impacts of CP and EP ENSO events, based in part on prevous work suggesting that EP events produce a north-south pattern of winter temperature anomalies over the US, while CP events produce an east-west oriented pattern.Beyond its scientific merit, the project has broader impacts due to the societal impacts of ENSO events. ENSO is the leading mode of short-term climate variability over the globe, and research to understand the dynamics and consequences of ENSO events could be instrumental in improving ENSO predictions. In addition, the work will support and train graduate and undergraduate students, as well as a postdoctoral researcher, thereby developing the scientific workforce in this area.