Climatological characterization of puelche winds down the western slope of the extratropical andes mountains using the NCEP climate forecast system reanalysis

The existence of strong easterly winds down the western slope of the south-central Andes in Chile, locallyknown as Puelche winds, has been known by the meteorological community since at least the mid-twentiethcentury. However, this is the first time that a climatological characterization of them is presented. The analysisis based on 36 yr of daily CFSR–NCEP reanalyzed data, validated by surface weather observations. Puelchewinds are present all year round. The main synoptic-scale forcing of Puelche winds in south-central Chile isthe passage of cold anticyclonic systems across the Andes Mountains. As these systems progress into theSouth American continent, a zonal surface circulation crossing from Argentina (upslope) to Chile (down-slope) develops. Unlike terral and raco, other foehnlike winds at subtropical latitudes in Chile, the Puelchewinds are forced by both meridional and zonal pressure gradients. Presumably, the smaller altitude of theAndes Mountains south of 358S allows the air crossing from east to west in response to the presence of themigratory high pressure system over Argentina. As in other places where foehnlike winds develop,the warming extends far from places where the Puelche is actually observed, that is, to the west of the Andesinto the surface at the coastal and the central depression areas. This ‘‘foehn clearance’’ is the result ofcloudless sky and drier atmosphere that would allow an increase in the solar radiation reaching the surfaceand a subsequent warming of the near-surface air. The foehn clearance also drives an enhanced nighttimecooling, especially on the days after the onset of the Puelche event