The Chilean Coastal Orographic Precipitation Experiment: Observing the influence of microphysical rain regimes on coastal orographic precipitation

Abstract

The Chilean Coastal Orographic Precipitation Experiment (CCOPE) was conducted during the australwinter of 2015 (May–August) in the Nahuelbuta Mountains (peak elevation 1.3 km MSL) of southern Chile(388S). CCOPE used soundings, two profiling Micro Rain Radars, a Parsivel disdrometer, and a rain gaugenetwork to characterize warm and ice-initiated rain regimes and explore their consequences for orographicprecipitation. Thirty-three percent of foothill rainfall fell during warm rain periods, while 50% of rainfall fellduring ice-initiated periods. Warm rain drop size distributions were characterized by many more and relativelysmaller drops than ice-initiated drop size distributions. Both the portion and properties of warm and ice-initiated rainfall compare favorably with observations of coastal mountain rainfall at a similar latitude inCalifornia. Orographic enhancement is consistently strong for rain of both types, suggesting that seeding fromice aloft is not a requisite for large orographic enhancement. While the data suggest that orographic en-hancement may be greater during warm rain regimes, the difference in orographic enhancement betweenregimes is not significant. Sounding launches indicate that differences in orographic enhancement are not easilyexplainable by differences in low-level moisture flux or nondimensional mountain height between the regimes.