In this study, reanalysis data and a long-term simulation with the regional climate model WRF (1982-2017; 10 km resolution) is used to analyze synoptic and regional processes associated with rainfall events in the Atacama Desert. Five composites, each with ten WRF-simulated rainfall events, are studied. They are selected based on a clustering and comprise the top winter events in South Atacama (23°-26°S), Southeast Atacama, and North Atacama (18-23°S), and the top summer events in North Atacama and Northeast Atacama.
Winter rainfall events in South Atacama are mostly associated with strong low-pressure systems over the Southeast Pacific and atmospheric rivers at their foreside, while cutoff lows occurring anomalously far north facilitate strong rainfall in North Atacama. Accordingly, tropical continental areas and the remote tropical and subtropical Pacific are identified as primary moisture sources, and moisture transport towards the Atacama Desert mainly takes place in the free troposphere (above 800hPa).
Strong summer rainfall events in North Atacama and Northeast Atacama are associated to a southward displaced Bolivian High. During rainfall events in North Atacama the high is shifted westwards when compared to the Northeast Atacama events. Consequently, Northern Chile is located at the northern periphery of the Bolivian High and the resulting strong easterlies may push strong convective systems from the Altiplano, towards the Atacama coast.
Detailed analyses of individual rainfall events reveal that the most important synoptic patterns associated with rainfall not only control the synoptic-scale moisture transport into the Atacama Desert, but also decisively influence the regional atmospheric circulation.