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- Title
Upwelling Shadows Driven by the Low‐Level Jet Along the Subtropical West Coast of South America: Gulf of Arauco, Chile.
- Authors
Mardones, Piero; Wong, Zeneida; Contreras‐Rojas, Josse; Muñoz, Richard; Hernández‐Miranda, Eduardo; Sobarzo, Marcus
- Abstract
Some semienclosed bays in the eastern boundary upwelling systems worldwide display a strong surface temperature gradient between cold water upwelled outside and warmer water inside these bays. This anomalous coastal temperature pattern is known as upwelling shadow (US). Research on this topic has mainly focused on identifying spatiotemporal patterns of US events, but the influence of the atmospheric synoptic variability on the temporal evolution of US events remains less well documented. This study uses observational, satellite‐derived, and reanalysis data to propose a mechanism that relates synoptic‐scale atmospheric phenomena with the development of US events in the Gulf of Arauco (GA), a highly productive and the largest semienclosed bay in central Chile (around 37°S). The mechanism associates the passage of migratory anticyclones over the study area with two key processes. The first process is the formation of a coastal low‐level wind jet, which intensifies the upwelling of cold subsurface waters outside the GA. We strongly suggest that the second one is the development of a coastal low pressure, which usually implies clear skies (increasing the solar radiation input) and weak downwelling favorable winds along the coast, factors that could largely explain the observed surface warming inside this embayment during these events. The presence of cold water upwelled offshore and the enhanced surface warming inside the GA, possibly also modulated by a weakened circulation, results in a strong thermal gradient with average temperature differences of more than 3°C, generating the US. Plain Language Summary: The wind‐driven upwelling is the rise of subsurface cold and nutrient‐rich water to the surface ocean. This process is typical of eastern boundary current systems, such as the west coast of South America. In this area, the South Pacific anticyclone, a high atmospheric pressure center that in summer migrates farther south, intensifies southerly winds enhancing the coastal upwelling process from approximately 40°S to the north. Some wind‐protected bays within the upwelling zones can get warmer than the cold upwelled water causing an upwelling shadow (US). The Gulf of Arauco (GA) is one of these bays and is particularly important for its high biological productivity and large size. This work suggests a mechanism connecting the development of US events with synoptic‐scale atmospheric phenomena. In particular, the passage of migratory high atmospheric pressure systems (migratory anticyclones) generates a wind jet that enhances coastal upwelling offshore this Gulf. Also, these anticyclones are associated with the onset of a low atmospheric pressure area along the coast (coastal low), which usually increase the radiation input contributing in part to warming within the Gulf, increasing the temperature differences (>3°C) between inside and outside the GA. Key Points: Synoptic‐scale atmospheric phenomena are directly related to the upwelling shadow events in the Gulf of AraucoThe coastal low‐level jet intensifies the southwesterly winds, enhancing coastal upwelling, and extending its area of influenceThe formation of a coastal low, which promotes an increase in the incoming solar radiation, can explain the unusual warming inside the gulf
- Subjects
PERSIAN Gulf; CHILE; OCEANIA; SOUTH America; UPWELLING (Oceanography); SOLAR radiation; BIOLOGICAL productivity; ANTICYCLONES; COASTS; ATMOSPHERIC pressure
- Publication
Journal of Geophysical Research. Oceans, 2022, Vol 127, Issue 8, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2021JC017979