18.5 Upstream orographic enhancement of midlatitude precipitation and cloud systems over the west coast of South America

Friday, 22 August 2014: 11:45 AM
Kon Tiki Ballroom (Catamaran Resort Hotel)
Maximiliano Viale, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago, R. Metropolitana, Chile; and R. D. Garreaud

Upstream orographic enhancement of precipitation and cloudiness from extratropical cyclones approaching the Andes from the Pacific Ocean was examined using rain gauge and CloudSat/CALIPSO satellite data. Transects with this observational base data from the Pacific Ocean to the lee of the Andes for different latitude bands (from 55ºS to 30ºS) were defined to explore variations of climatological precipitation and clouds' properties in the cross-barrier direction. In all transects south of 35ºS and up to 43ºS (where rain gauge data was available), the precipitation amounts over the foot of the Andes were 1.5 to 2 times greater than that observed on the coast. This upstream rain enhancement factor remains relatively constant regardless the latitude and season of the year, and despite the variation in the barrier altitude and baroclinic activity. Moreover, rain frequencies indicate an increase from the coast to the foot of the Andes, at sub-daily or hourly time scales (but not at daily time scale) suggesting an intensification and/or a longer duration of the synoptic-scale precipitation systems with decreasing distance from the mountain range. CloudSat/CALIPSO satellite data allows expanding the investigation of cloud properties southward up to the end of the Continent, and eastward up to the lee side of the Andes. Coherent with rain gauges data, cloud frequency, ice and liquid water content, among other variables derived from the CloudSat 2B-GEOPROF/LIDAR and 2B-CWC-RVO products, show a local increase on the western slopes of the Andes, as well as depict an abrupt decrease on the eastern slopes and on the lee of the Andes.
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