Orographic effects of the subtropical and extratropical Andes on precipitating clouds

BIANCHI E.; VIALE M.; ZALAZAR G.

Reykjavík

Conferencia; 34th International Conference on Alpine Meteorology; 2017

University of Iceland

The orographic effect of the Andes (35°S-50°S) on precipitating clouds from midlatitude frontal systems is investigated using surface and CloudSat satellite data. The Andes is a long mountain chain that extends in the north-south direction on the west coast of South America. Its crest descent from the subtropics to extratropics and its perpendicular disposition to the westerly makes this barrier an excellent natural laboratory to investigate orographic effects on frontal precipitation systems. Seven transects of hourly rain gauges between 35°S and 45°S from the windward side (Chile) to the lee side (Argentina) were installed as part of a project initiated in 2016. Installed rain gauges were complemented with daily precipitation data managed by Argentinean and Chilean Weather and Water agencies, although these datasets do not sample well near the crest and in the immediate lee sectors of the Andes. Surface precipitation observations indicate orographic enhancement and suppression in annual total amount from the Pacific coast to the leeward slopes that varies with latitude. Hourly gauges and instantaneous satellite observations show that the cross-barrier increase and decrease in annual precipitation responds to increase and decrease in both the intensity and frequency of precipitation. In addition, CloudSat satellite data reveal cross-barrier variations in precipitating cloud properties that suggest orographic influences on the airflow dynamics and microphysical processes that will be discussed in the presentation.