Abstract
The Southeast Pacific Subtropical Anticyclone (SPSA) extends over the entire South Pacific Basin and it is the dominant forcing of the Humboldt Current System. The SPSA has seasonal, interannual, and decadal (interdecadal) variability. The latter variability has been associated with the Pacific Decadal Oscillation (PDO), recognized as a Pan-Pacific mode. However, most of the ocean–atmosphere studies on interdecadal scales have been conducted in the Northern Hemisphere, and very few in the Southern Hemisphere. Thus, through reanalysis model outputs and satellite data, this research mainly establishes the relationship between SPSA and PDO in the period 1949–2012 and its impact on sea surface temperature along the north-central coast of Chile between 2000 and 2012. For this purpose we first analyzed the seasonal and interannual variability of the SPSA. An analysis of correlation between air pressure at sea level and the PDO and Southern Annular Mode (SAM) indices established that, at the interdecadal scale, these oscillations explained 49% and 40% of the variance, respectively; however, SAM had a time lag of six years to explain this variance. The PDO, in the air pressure field, produced similar changes to El Niño–Southern Oscillation. Over the past 13 years, the SPSA has intensified and shifted toward the southwest, increasing the offshore Ekman transport and Ekman suction, which would explain much of the observed coastal cooling south of 33º S (central Chile).
Highlights
The circulation in the surface layer of large subtropical gyres is mainly driven by the winds (Huang and Russell 1994) flowing around high pressure centers known as anticyclones
In the austral summer the Southeast Pacific Subtropical Anticyclone (SPSA) is more intense off the coast of central-southern Chile and in winter it is more intense off the coast of La Serena (Taljaard 1972)
The seasonal variation in the intensity of the SPSA showed a semiannual behavior with maximum intensity in February and October
Summary
The circulation in the surface layer of large subtropical gyres is mainly driven by the winds (Huang and Russell 1994) flowing around high pressure centers known as anticyclones. The vertical and horizontal motion in these gyres plays a fundamental role in controlling the ocean–atmosphere interaction, and is of importance for our understanding of the oceanic general circulation and climate variability at different time scales. Along the coast of Peru, the SPSA generates upwelling-favorable winds that are more intense in winter than in summer. These alongshore coastal winds advect water northwards and cause offshore Ekman transport, with the consequent upwelling of water from deeper layers (Croquette et al 2007). When the SPSA is stronger the magnitude of the southerly winds increases and so does the transport of water from the pole and the occurrence of upwelling (Croquette et al 2007). When it weakens, the magnitude of the southerly winds decreases and Ekman transport occurs less frequently
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