Neural network forecasts of the tropical Pacific sea surface temperatures

Aiming Wu, William W. Hsieh and Benyang Tang

A neural network (NN) model had been used by our group to predict the SST anomalies in the Nino3.4 region in the equatorial Pacific (Tang et al, 2000). The NN model has been extended to forecast the SST anomalies over the entire tropical Pacific, and in the latest version 3.2 (introduced in Dec. 2004), it has also added subsurface temperature anomalies as predictors, which enhanced the model forecast skills. Click here to see details about this model.

Using sea level pressure, sea surface and subsurface temperature data up to the end of October, 2005, forecasts were made with the NN model. Ensemble-averaged forecasts for the sea surface temperature anomalies (SSTA) in the Nino3.4 region at various lead times are shown in Fig.1, showing a slightly cool eastern equatorial Pacific in winter, turning to a slightly warm central equatorial Pacific in spring. The forecasted SSTA fields over the tropical Pacific are shown in Fig.2.

Figure 1. The SSTA (in degree Celsius) in the Nino3.4 area (170W-120W, 5S-5N) predicted by the ensemble-averaged nonlinear model at 3, 6, 9 and 12 months of lead time (circles), with observations denoted by the solid line. Tick marks along the abscissa indicate the January of the given years. (The postscript file of Fig.1 is also available).
Figure 2. SSTA (in ºC) predicted by the ensemble-averaged nonlinear model at 3, 6, 9 and 12 months of lead time, corresponding to the four consecutive seasons starting with DJF (December, 2005 - February, 2006). The zero contour is shown as a thick black curve. (The postscript file of Fig.2 is also available).
Data in tabular format for the Nino3.4 SSTA (in ºC) at 3, 6, 9 and 12 months of lead time:
DJF2006 -0.36
MAM2006 0.51
JJA2006 0.45
SON2006 0.62


Reference
Tang, B., W.W. Hsieh, A.H. Monahan and F.T. Tangang, 2000. Skill comparisons between neural networks and canonical correlation analysis in predicting the equatorial Pacific sea surface temperatures. J.Climate, 13: 287-293.

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