Predicting the '97 El Nino event with a global climate model

Abstract

A global climate model is used for hindcasting the '97 El Ni no event. For this purpose a simple data assimilation technique has been developed which generates the thermal state of the low-latitude oceans by forcing the model with observed sea surface temperature (SST) anomalies. In this assimilation experiment, the vertical temperature profiles in the subsurface equatorial Pacific measured by the TOGA-TAO array were successfully simulated for the period 1996-1997. In a further series of eight hindcast experiments, initialized between January 1996 and October 1997, the predictive skill of the model was tested. All experiments starting in 1997 correctly simulated the evolution of the '97 El Ni no, although the amplitude was slightly underestimated. The model also predicted a dry period in the Indonesian region during fall 1997 when extensive forest fires occurred in this area. While the ocean was preconditioned to create an El Ni no already in 1996, the model correctly stayed in the cold (La Ni na) phase. All experiments initialized in '97 forecast a La Ni na event for the middle of '98. This is also suggested by the subsurface thermal structure in the tropical equatorial Pacific with a strong cold anomaly propagating eastward according to both, TOGA-TAO data and the data assimilation experiment. (orig.)18 refs.Available from TIB Hannover: RR 1347(254) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman