Characteristics of the Orographic Precipitation Observed by Profiling Radar during the Chilean Orographic and Mesoscale Precipitation Study over the Southern Andes Mountain Range.

The Andes Cordillera is the major mountain range in the Southern Hemisphere, with heights ranging from 1000-1500 m in the south of the continent to 6000 m at the Equator. The interaction of frontal systems with this mountain range leads to an enhancement of precipitation due orography, which can cause floods and landslides in the valleys of central Chile. In other regions of the globe with mountain ranges in middle latitudes, such as the Sierra Nevada in the western of United States, the influence of the orography on the precipitation pattern, more specifically, the roles of rain regimes, such as ice-initiated and warm rain periods, and vertical profiles of precipitation, have been investigated extensively, but in the Southern Hemisphere these roles remain to be investigated, due the lack of long-term precipitation records, high elevation data and operational radar coverage.

This study focuses on The Chilean Orographic and Mesoscale Precipitation Study (ChOMPS) which collected data from three vertically profiling Micro-Rain-Radars (MRRs), two Parsivel disdrometers and three meteorological stations, for three locations along a zonal transect at ~36ºS: a coastal site (Concepción, 50m MSL), a central valley site (Chillán, 138m), and a mountain site (Las Trancas, 1235m), from May through October 2016 corresponding to austral winter. ChOMPS provided data unique until now, allowing for the study of mesoscale precipitation processes in the Chilean Andes.

Using MRR data, we objectively classify non-convective rainfall periods as associated with either ice-initiated rain or warm rain microphysical regimes based on the presence or absence of a well-defined melting layer. We calculate statistics to compare between both regimes and transect locations, including: rainfall amount associated with each regime, drop-size distribution, strength of orographic enhancement and frequency of each regime. For ice-initiated periods, we calculate spatial variations in height of the melting layer. These result can be compared with studies in the western coast of the United States, due the similarity between the Sierra Nevada and the Andes topography and location.