Cooperative Institute for Research in Environmental Sciences

Science Rendezvous > 2009 Posters
The presenter is listed in italics. All poster presentations are the property of their respective authors. Please contact the authors for permission to use images, information, or ideas.

The Role of ENSO in Regulating its Background State

De-Zheng Sun and Tao Zhang

Linear theories for ENSO have the background state prescribed, leaving the question whether ENSO in turn plays a role in determining the background state unaddressed. Answering this question, however, is critical for addressing a number of climatic issues including how ENSO responds to anthropogenic forcing. In this talk, I will presentresults from numerical experiments with a coupled model to suggest that ENSO regulates the stability of the time-mean state of thecoupled tropical Pacific ocean-atmosphere system. In the absence of ENSO, the time-mean difference between the warm-pool SST (Tw) and the characteristic temperature of the equatorialthermocline (Tc) responds sensitively to either enhanced tropical heating or enhanced extratropical cooling. In the presence of ENSO, such sensitivity to destabilizing forcing disappears. This is because ENSO becomes stronger in response to such destabilizing forcing.The stronger ENSO then results in more vigorous sloshing of water in the equatorial upper ocean. Through downward pumping during La Ninaand horizontal redistribution during El Nino, ENSO acts as a basin scale "heat mixer" that prevents any significant increase from occurring in the time-mean difference between Tw and Tc. The results underscore the nonlinear and diabatic nature of ENSO, and suggest a new paradigm to understand the response of ENSO to global warming. The new paradigm is then applied to understand the causes of the recent elevation of ENSO activity.