A Tropical Rainfall Measuring Mission (TRMM) rainfall climatology west of the Chilean Andes

The Andes impact tropospheric circulation on a broad range of scales, generating mesoscale barrier jet flows and disrupting the progression of frontal boundaries. West of the Andes, the Southeast Pacific Ocean is one of the major global regions for cyclogenesis, and low pressure systems that form there move eastward and equatorward, progressing north along the windward side of the Andes.

A recent study examined one such low pressure system and its associated cold front from May 2008. As it approached the west coast of South America, its cyclonic circulation advected moist, near-surface air from the subtropics poleward ahead of the cold front. Low-level flow blocking by the Andes channeled this moisture to the south, enhanced convergence along the cold front, and organized a distinct “coastal” precipitation region that behaved differently than precipitation offshore or over the mountains.

Although the 2008 event was studied closely, it is not known if the character of its precipitation – specifically the temporal and spatial distribution of rainfall and rainfall intensity – is representative of a low pressure system windward of the Chilean Andes. Using Tropical Rainfall Measuring Mission (TRMM) observations from May 1998 to May 2010, an observational climatology of winter-season rain events in central Chile was developed. Preliminary results showed a persistent precipitation zone, similar to the “coastal” region of the May 2008 event. Furthermore, maximum TRMM precipitation was observed in the region between Santiago and Concepcion but only extended 100 km offshore. Additional results will be presented with as the TRMM data are further analyzed.