Dominant Wind Patterns Under the Influence of Atmospheric Rivers: Implications for Coastal Upwelling off Central-Southern Chile

Abstract

Atmospheric rivers (ARs) trigger intense precipitation and strong winds along the western coasts of mid-latitude continents. While the terrestrial impacts of ARs have been extensively studied, their influence on the ocean environment remains poorly understood. Here, we investigate several ARs affecting the Ekman dynamics along the coastal ocean off central-southern Chile from 1979 to 2018. A compositing method was applied to capture the general atmospheric and oceanographic responses to ARs, using reanalysis, satellite and in-situ data. Two primary patterns of ARs are described in the region: tilted (TAR), with a predominant northwest-southeast orientation and zonal (ZAR), with a prevailing west-east orientation. A total of 2480 events were quantified: 1243 TARs and 805 ZARs, with the remaining events being excluded from this study. The wind pattern associated with TARs induces stronger downwelling along the coastal ocean near the landfall areas, leading to increases in SST, southeastward surface currents, and higher sea levels. Additionally, a rise in sea level and SST north of the TAR axis suggests upwelling relaxation in areas farther north of the landfall. In contrast, ZARs have a minimal impact on downwelling, resulting in variable effects on SST and sea level. North of the ZAR axis, the intensification of atmospheric anticyclones triggers upwelling conditions along the coast, leading to a decrease in SST and sea level, accompanied by northwestward surface currents. The frequency of ZARs has shown an increasing trend in recent years, while TARs exhibit a decreasing trend, suggesting a potential increase in upwelling events associated with ARs.