Upstream orographic enhancement of precipitation from extratropical cyclones over the west coast of South America

VIALE, M.; GARREAUD, R. D.

Santiago

Congreso; III Congreso de Oceanografia Fisica, Meteorologica y Clima del Pacifico Sur Orienta; 2013

Upstream orographic enhancement of precipitation from extratropical cyclones approaching the Andes from the Pacific Ocean is examined using daily rain gauge and CloudSat satellite data. Transects with this observational data from the Pacific coast to the foot of the Andes for different latitude bands were defined to explore variations of climatological precipitation and cloud frequency in the cross-barrier direction. In all the transect south of 35ºS and up to 43ºS (where there is available gauge data), the precipitation amounts over the foot of the Andes are 1.5 to 2 times greater than that observed on the coast. This upstream enhancement factor remains relatively constant regardless the latitude and season of the year, and despite the variation in the barrier altitude and baroclinc activity. Cloud frequency, derived from the CloudSat 2B-GEOPROF reflectivity product, depict a local increase of cloudiness on the western face of the Andes with respect to that observed on the open ocean and the coast. Meanwhile, frequencies of rainy days from rain gauges indicate a minimal or no-increase from the coast to the foot of the Andes, suggesting an intensification of the synoptic-scale precipitation systems with decreasing distance from the mountain range, rather than an increase in frequencies of rain events.