Climatological aspects of the 1991/1993 El Niño in Ecuador

Abstract

In the scope of the project ENPEX (El Niño Precipitation Experiment), the spatial distribution and temporal development of severe precipitation in Ecuador and northern Peru during the 1991/1993 El Niño event have been investigated mainly based on satellite data (METEOS AT-3). The distribution of heavy rains is determined by the Convective-Stratiform-Technique (CST) which has been adjusted to METEOS AT-3 geometry as well as the KED interpolation method. The validation of the adjusted CST scheme reveals an encouraging accuracy also for extreme rainfall amounts up to 300 mm per 3 days. The extraction of cloud motion winds (CMW) by means of cross correlation technique which is applied to sequences of METEOS AT imagery provides additional information on circulation patterns which are related to severe precipitation. The analysis have shown that the 1991/1992 event is stronger than the 1972/1973 but significantly weaker than the 1982/1983 event. Severe precipitation occurs mainly in the coastal plain of Ecuador and north Peru up to the 1000 m contour line. Deep convection is originated by the land-sea-breeze phenomenon on most of the investigated days. In this case, heavy precipitation is locally confined and shows a clear diurnal cycle. Precipitation starts over land in the evening and is shifted to the coastal waters during night. A nocturnal center of heavy precipitation is the Gulf of Guayaquil due to the shape of the coastline which favours convergence and the frequently increased SST’s. in this area. Severe precipitation without any diurnal cycle which is characterized by great spatial extension occurs during main El Niño (March-April) due to an extended atmospheric instability of the lower troposphere. Deep convection is often organized in mesoscale convective complexes (MCC) which are related to extended areas of SST’ s >28oC. During these situations, a strong meridional stream flow (Hadley circulation) could be observed.