Westerly Wind Events and the 1997/98 El Niño Event in the ECMWF Seasonal Forecasting System: A Case Study

Abstract

Abstract The 1997/98 El Nino was one of the strongest on record. Its onset was predicted by several numerical models, though none fully captured its intensity. This was the case for the ECMWF seasonal forecasting system that underestimated the intensification during the June–July 1997 period by more than 1 K. Several strong westerly wind events developed during the onset of the 1997/98 El Nino suggesting that westerly wind events played a key role in the intensification of this El Nino. The present paper quantifies the impact of westerly wind events on the 1997/98 El Nino in the ECMWF seasonal forecasting system, through a series of experiments in which various modifications are made to convective parameterization and wind forcing to increase wind variability in the western Pacific. The ECMWF model does not produce significant westerly wind events. A set of experiments suggests that if the model were able to simulate the May–June westerly wind event, it would have predicted significantly warmer Nino-3 (5°...