Abstract

Hemispheric, synoptic and regional-local scale meteorological conditions associated with the occurrence in Chile of two debris flows with catastrophic consequences are described. In both events high intensities and large spacial variability were observed. In the Antofagasta case, which occurred at dawn on June 18, 1991, the convective development of a frontal disturbance was produced by the release of potential instability. In the second debris flow, that affected especially the city of Santiago during the morning of May 3rd, 1993, the convection developed through the release of conditional instability. The regional-local elements that favored the release of instability in each case are described, including estimates of the return period of the most characteristic meteorological elements. In the hemispheric and regional scales it is shown that both episodes developed in the general context of anomalies associated with the El Niño-Southern Oscillation (ENSO) events. In the case of Antofagasta, the extraordinary persistence of a positive anomaly of the geopotential heights through out the troposphere to the southwest of the southern tip of South America was paramount. In the Santiago episode, the most relevant aspect was the extraordinary extension to the subtropics of the anomalous heating of the tropical troposphere, characteristic of the mature phase of ENSO events.