Collaborative Research: Westerly Wind Bursts: El Nino Southern Oscillation's (ENSO) Driver or Slave?

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Westerly wind burst (WWB) events are known to play an important role in El Nino Southern Oscillation's (ENSO) dynamics. The events are usually viewed as stochastic forcing that is independent of and external to the large scale ENSO dynamics. There are indications, however, that the occurrence of these events, and their characteristics, are influenced by the large scale SST structure, and hence by ENSO. This study will explore the dynamical consequences of the possibility that the timing and other characteristics of WWB events are partially regulated and controlled by the large scale SST distribution. That is, the study will examine the extreme possibility that these events occur only when the large scale SST structure is at a certain configuration. For example, when the warm pool is extended eastward beyond the dateline. In this scenario the WWB events will be treated as an inherent part of the deterministic ENSO dynamics rather than as external stochastic forcing. The study will first analyze observations in order to try and establish the characteristics of such a possible regulation of the timing or characteristics of WWB events by the large scale SST field. Next, the implications of such regulated switching of WWB events by the large scale ENSO dynamics will be studied using a hierarchy of models. The model hierarchy will include a hybrid coupled model (ocean general circulation model coupled to a statistical atmosphere), an intermediate coupled model, and a conceptual delayed oscillator model. Broader impacts of the research include possible improvement of ENSO's prediction skill, should the proposed research find a way to include a representation of WWB regulation by the large scale SST field in current ENSO prediction models. A graduate student (under Mark Cane) and a post-doc (under Eli Tziperman) will be educated, mentored and trained under this grant.