WINDWARD-SIDE OROGRAPHIC EFFECTS OF THE SUBTROPICAL AND EXTRATROPICAL ANDES ON PRECIPITATING CLOUDS

VIALE MAXIMILIANO; GARREAUD RENE D.

Mar del Plata

Congreso; Congreso Argentino de Meteorologia CONGREMET 2015; 2015

Centro Argentino de Meteorologia

The orographic effect of the Andes (30°S-55°S) on windward-side precipitating clouds from mid-latitude frontal systems is investigated using surface and satellite data. Rain gauges between 33°S and 44°S indicate that annual precipitation increases from the Pacific coast to the windward slopes by a factor of 1.6 ± 0.2. Hourly gauges and instantaneous satellite estimates reveal that the cross-barrier increase in annual precipitation responds to an increase in both the intensity and frequency of rainy events. Orographic effects of the Andes are stronger at subtropical (30°S-40°S) than at extratropical latitudes (40°S-55°S) according to CloudSat satellite data. To the south of 40°S, the depth of the cloud layer slightly decreases from offshore to the Andes. The total ice content changes little in the cross-mountain direction, but the maximum ice content over the windward slopes is larger and occurs at a lower level than its counterpart offshore. These results suggest that ice particles aloft are produced by synoptic-scale ascent but low-level orographic lifting accentuate the riming process, thus accelerating the particles growth and fall out over the extratropical Andes. At subtropical latitudes, the clouds over the ocean are shallow and contain minimal ice aloft. The total and maximum ice content significantly increases toward the tall subtropical Andes, with values being much higher than their counterparts over the extratropical Andes. Further, the increase in ice content starts before the barrier, likely as a result of upstream blocking.