Atmospheric Rivers impacting the West Coast of South America

GARREAUD R. D.; VIALE M.

Conferencia; 2nd International Atmospheric Rivers Conference; 2018

Scripps Institution of Oceanograph

This study quantifies the impact of atmospheric rivers (AR) on precipitation in southern South America. An AR detection algorithm was developed based on integrated water vapor transport (IVT) from six-hourly CFSR reanalysis data over a 15-year period (2001-2016). AR landfalls were compared to a comprehensive precipitation observing network that spanned large variations in terrain across the Andes from 27°S to 55°S, including some sites with hourly precipitation data. Along the Pacific (west) coast, AR landfalls are most frequent between 38°S and 50°S, averaging 35-40 days/year. This decreases rapidly to the south and north of this maximum and to the east of the Andes, with just 10 AR days/year at 31°S, for example. Landfalling ARs are more frequent in winter/spring (summer/fall) to the north (south) of ~43°S. ARs contribute 50%-65% of the annual precipitation in subtropical Chile (38°S-32°S) and 40%-55% along the midlatitude west coast (38°S-47°S). These values significantly exceed those in western North America, likely due to the Andes being taller. In subtropical and midlatitude regions roughly half of all events with top-quartile precipitation rates occur in ARs. Median daily and hourly precipitation in ARs are 2-3 times that of other storms. The results of this study extend knowledge of the key roles of ARs on precipitation, weather and climate in the South American region. They enable comparisons with other areas globally, and support local forecasting and applications development.