Climatology of rainfall and wind for the Philippine-South Sea region: 2. Variations due to El Nino and La Nina

The characteristics of rainfall and wind during the occurrence of three El Nino episodes and one La Nina episode are studied by using observational data. The episodes correspond to the El Nino of the years 1983, 1987, and 1992, and the La Nina year of 1989. The data consist of gridpoint values of rainfall and wind from the European Centre for Medium-Range Weather Forecasts (ECMWF) and raingauge observations from Philippine stations. The analysis of the ECMWF data shows that there are relatively large differences in the rainfall anomaly patterns between individual El Nino years. Furthermore, these anomaly patterns are quite different from a long term composite El Nino anomaly pattern.

The rainfall anomaly pattern during the winter for the La Nina of 1989 shows a well-defined elliptical area of large positive anomalies just east of the Philippines. This pattern is roughly similar to that of a long-term composite pattern. The elliptical area coincides with a cyclonic pattern in the wind anomaly.

Rainfall anomalies at raingauge stations are compared with those of the nearest ECMWF gridpoints. The results of the comparison show good agreement in some cases where the gridpoints are near raingauge station. But, in general, the agreement is poor. The poor agreement is due to either the coarse resolution of the ECMWF data or inherent errors in the ECMWF analysis. On the basis of the study, one concludes that it is extremely difficult to predict
rainfall anomalies over small regions in the Philippines during ENSO episodes with the aid of dynamical climate