Journal Article A new Approach to El Nino Prediction beyond the Spring Season

増田, 周平  ,  MATTHEWS, John  ,  石川, 洋一  ,  望月, 崇  ,  田中, 裕介  ,  淡路, 敏之  ,  MASUDA, Shuhei  ,  MATTHEWS, John  ,  ISHIKAWA, Yoichi  ,  MOCHIZUKI, Takashi  ,  TANAKA, Yusuke  ,  AWAJI, Toshiyuki

5p.16782 , 2015-11-25 , Nature Publishing Group
The enormous societal importance of accurate El Nino forecasts has long been recognized. Nonetheless, our predictive capabilities were once more shown to be inadequate in 2014 when an El Nino event was widely predicted by international climate centers but failed to materialize. This result highlighted the problem of the opaque spring persistent barrier, which severely restricts longer-term, accurate forecasting beyond boreal spring. Here we show that the role played by tropical seasonality in the evolution of the El Nino is changing on pentadal (five-year) to decadal timescales and thus that El Nino predictions beyond boreal spring will inevitably be uncertain if this change is neglected. To address this problem, our new coupled climate simulation incorporates these long-term influences directly and generates accurate hindcasts for the 7 major historical El Ninos. The error value between predicted and observed sea surface temperature (SST) in a specific tropical region (5°N-5°S and 170°-120°W) can consequently be reduced by 0.6 Kelvin for one-year predictions. This correction is substantial since an "El Nino" is confirmed when the SST anomaly becomes greater than +0.5 Kelvin. Our 2014 forecast is in line with the observed development of the tropical climate.

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