Background
A primary cause for aridity in the Atacama Desert is its location at the eastern boundary of the subtropical Pacific. In that region, large-scale atmospheric subsidence produces dry, stable conditions and maintains a surface anticyclone over the southeast Pacific that hinders the arrival of mid-latitude disturbances (Takahashi and Battisti, 2007). The subtropical anticyclone drives equator-ward winds along the coast that, in turn, foster the transport of cold waters from higher latitudes (i.e. the Humboldt or Chile-Peru surface current). The upwelling cold Humboldt Current inhibits the moisture capacity of onshore winds by creating a persistent inversion that traps any Pacific moisture below ~1000 m above sea level (Houston, 2006a; Rutllant et al., 2013) and leads to the formation of a persistent deck of stratus clouds (Cereceda et al., 2008a; Rutllant et al., 2003; Takahashi and Battisti, 2007). These factors result in a marked regional cooling of the lower troposphere that is compensated by enhanced subsidence along the Atacama coast (Takahashi and Battisti, 2007) further drying this area. Finally, the pronounced rain shadow effect of the Andes to the East effectively inhibits moisture transport from the East (Houston and Hartley, 2003; Rech et al., 2010; Takahashi and Battisti, 2007). The high evaporation potential in most sections of the Atacama (Houston, 2006a) provides the finishing touch to the hyperarid conditions.
