Neural-dynamical hybrid coupled model forecasts of the tropical Pacific sea surface temperatures

contributed by Youmin Tang and William Hsieh

Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, B.C. V6T 1Z4, Canada

The forecast model is the neural-dynamical hybrid coupled model used in our previous forecasts (Tang and Hsieh 2001a), but the NCEP sea level height anomaly (SLHA) data set is used (instead of the upper ocean heat content data) to initialize the forecast, simply because the NCEP SLHA is more quickly updated. The assimilation of the NCEP SLHA yields as great an improvement in the forecast correlation skills as the assimilation of heat content anomalies (Tang and Hsieh 2001b). Fig. 1 shows the correlation skills of the predicted SST anomalies (SSTA) in the NINO3 region in the equatorial eastern Pacific during 1990-1999 using our model with SLHA assimilation. The predictions were made at three months intervals (starting on 1 January, 1 April, 1 July and 1 October) and continued until a lead time of 15 months.

Fig. 1 Correlation of the predicted NINO3 SSTA for the period 1990-99 which remains above 0.6 for 15 month lead time. Fig. 2 shows the prediction of the NINO3 SSTA starting from 1995 to 2001 at lead times of 6 months and 12 months.

Fig. 3 shows our latest forecasts (initialized using data till the end of October, 2001), indicating that the moderate cool anomalies present during spring, 2002, will further intensify towards La Nina conditions by summer, 2002, and continuing onto fall and winter.

References:

Tang, Y. and W.W. Hsieh, 2001a: Neural-dynamical hybrid coupled model forecasts of the tropical Pacific sea surface temperatures. Experimental Long-Lead Forecast Bulletin, Mar. and June 2001.

Tang, Y. and W. W. Hsieh, 2001b: Impact of data assimilation on ENSO simulations and predictions in a hybrid coupled model framework. J. of Climate (submitted).

Figure Captions:

Fig.1 Correlation skills of the predicted NINO3 SSTA.

Fig. 2 shows the prediction of the NINO3 SSTA starting from 1995 to 2001at lead times of 6 months and 12 months.

Fig.2 Observed and predicted NINO3 SSTA at lead times of 6 and 12 months.

Fig 3 shows our latest forecasts (initialized using data till the end of October, 2001), indicating that the moderate cool anomalies present during spring, 2002, will further intensify towards La Nina conditions by summer, 2002, and continuing onto fall and winter.

Fig.3 Predicted SSTA of the tropical Pacific. Contour interval is 0.5 degree Celsius, with positive anomalies indicated by solid contours, negative anomalies by dashed contours, and zero by thick contours. Shaded areas indicate anomalies of magnitude exceeding 1 degree.