Interannual and Decadal Variability in the Equatorial Pacific Atmosphere and Ocean

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Preliminary research shows that the decadal and longer variability of our best known El Nino Southern Oscillation (ENSO) indices are poorly correlated before 1950. Without an accurate knowledge of these indices, it is impossible to assess how decadal and longer changes in the atmosphere and ocean affect, for example, the size and frequency of El Nino events. The two major goals of this research are to derive accurate long records of key ENSO indices and to use them and an ocean model to test observational and theoretical conjectures about interannual and decadal ocean-atmosphere variability in the equatorial Pacific. The PI's goals are: 1. Obtain long record of key ENSO indices that are accurate on interannual and decadal and longer time scales. Even the best estimates of key ENSO sea surface temperature (SST) indices like NINO3.4 (the SST anomaly averaged over the east-central equatorial Pacific region 5S-5N, 170W-120W) have only used SST data to estimate that index. In this project other data that are closely linked physically to the index data will be used to help estimate and verify the index. The analysis will also take advantage of the calendar-year phase-locked properties of ENSO indices and will include previously unavailable recently digitized historical data. A key aspect of the analysis is that the ENSO indices will be checked against each other for accuracy using simple dynamical balances. 2. Test observationally-and theoretically-based ENSO conjectures. The PI will use the time series derived in 1, together with an analytical/numerical model, to address questions resulting from observationally and theoretically based conjectures. Does El Nino/La Nina amplitude depend on longer term changes in the underlying ocean state? Are there really asymmetries in the discharge/recharge ENSO oscillator paradigm? Do these asymmetries depend on decadal variability? Does the discharge/recharge oscillator paradigm operate on decadal time scales? Broader Impacts. It is planned that a nearly completed book 'El Nino and the Southern Oscillation Dynamics," which is based on the PI's course and this research, will be useful to graduate students and researchers both within and outside of Florida State. ENSO climate fluctuations influence agriculture, water resources, fisheries, the number of hurricanes and wildfires, energy needs for heating/cooling and the prevalence of famine and disease in certain regions. Achievement of the goals of this research will lead to increased understanding of ENSO and the influence of decadal changes on it. This should enable the PI to predict ENSO better, particularly in the case of statistical prediction models which may be non-stationary under decadal changes.