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|Subject: el nino||Date: 4/20/2004 1:43 PM|
|Author: solasis||Number: 275 of 295|
Abstract of article in Nature:
Predictability of El Niño over the past 148 years
DAKE CHEN1,2, MARK A. CANE1, ALEXEY KAPLAN1, STEPHEN E. ZEBIAK1 & DAJI HUANG2
1 Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964, USA 2 Laboratory of Ocean Dynamic Processes and Satellite Oceanography, State Oceanic Administration, Hangzhou, China Correspondence and requests for materials should be addressed to D.C. (email@example.com). Forecasts of El Niño climate events are routinely provided and distributed, but the limits of El Niño predictability are still the subject of debate. Some recent studies suggest that the predictability is largely limited by the effects of high-frequency atmospheric 'noise'1-7, whereas others emphasize limitations arising from the growth of initial errors in model simulations8-10. Here we present retrospective forecasts of the interannual climate fluctuations in the tropical Pacific Ocean for the period 1857 to 2003, using a coupled ocean–atmosphere model. The model successfully predicts all prominent El Niño events within this period at lead times of up to two years. Our analysis suggests that the evolution of El Niño is controlled to a larger degree by self-sustaining internal dynamics than by stochastic forcing. Model-based prediction of El Niño therefore depends more on the initial conditions than on unpredictable atmospheric noise. We conclude that throughout the past century, El Niño has been more predictable than previously envisaged.
From the original article in Nature:
"In summary, we have performed a retrospective ENSO forecast experiment for the past one-and-a-half centuries, which is several times longer than any previous experiments of this kind. Although the model was trained with recent data, it showed high skill in predicting the historic El Niño events back to the nineteenth century. Most importantly, we demonstrated that the large El Niños are predictable at long lead times. As our model has a self-sustaining internal oscillation and it does not invoke any stochastic forcing, this suggests that predictions depend more on initial conditions that determine the phase of ENSO, than on unpredictable atmospheric noise. Although westerly wind bursts do affect the exact onset time and perhaps the amplitude of El Niño, the gross features of ENSO seem to be coded in the large-scale dynamic state. Our results favour the interpretation that the enhanced wind burst activity in the boreal spring preceding large El Niño events is a consequence of those ongoing events27 rather than a cause1. A practical consequence of our results is a more optimistic view of the possibility of skilful long-lead forecasts of El Niño."
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