Influence of large scale oscillations on upwelling-favorable coastal wind off central Chile

• Published in: Journal of Geophysical Research: Atmospheres 2012-10, Vol.117 (D19), p.n/a
• Main Author: Rahn, David A.
• Format: Article
• Language: English
• Subjects: AAO; Atmospheric sciences; Chile; Climate science; Climate system; coastal upwelling; Earth sciences; Earth, ocean, space; ENSO; Exact sciences and technology; Geophysics; MJO; Oceanography; Sea level; Upwelling; Wind speed
• ISSN: 0148-0227; 2169-897X; 2156-2202; 2169-8996
• DOI: 10.1029/2012JD018016

Along the central coast of Chile is typically equatorward, upwelling‐favorable wind associated with the southeast Pacific anticyclone. A coastal low‐level jet often develops, and its wind speed is mostly controlled by the meridional pressure gradient. While the low‐level jet is a mesoscale feature forced by an interaction between synoptic conditions and coastal topography, regional sea level pressure anomalies are associated with changes of the Antarctic, Madden Julian, and El Niño–Southern Oscillation. The connection between the alongshore wind and changes to the large‐scale circulation is examined and quantified using 31 years of the Climate Forecast System Reanalysis, which resolves coastal features better than previous, coarser analyses. Composites based on each index reveal the modulation of the sea level pressure and significant alongshore wind anomalies of ±0.5–1.5 m s−1 that correlate well to meridional surface pressure gradient changes and are centered near 35°S. Constructive and destructive interference exists between the three indices that either enhance or cancel the alongshore wind anomaly. During favorable upwelling conditions the distribution of meridional wind is generally clustered around positive anomalies with a tail toward negative values, representing a stronger and persistent anticyclone. During unfavorable upwelling conditions the anomalies are generally more normally distributed, representing a weaker anticyclone and the passage of more cyclones. Key Points Phases of AAO, ENSO, and MJO linked to alongshore wind off central Chile Constructive/deconstructive interference between large scale oscillations Significant modification of alongshore wind distribution