Modes of covariability between sea surface temperature and wind stress intraseasonal anomalies along the coast of Peru from satellite observations (2000-2008)
Résumé
The Tropical Rainfall Measuring Mission Microwave Imager sea surface temperature (SST) and QuikSCAT wind stress satellite data are used to investigate the intraseasonal upwelling variability along the coat of Peru over the period 2000-2008. Two regions of peak variance correspond to the central Peru region (Pisco region, 15 degrees S) and the northern Peru region (Piura region, 5 degrees S). A covariance analysis reveals a significant coherency between winds and SST anomalies off Pisco, consistent with Ekman pumping and transport dynamics. The upwelling cell consists in a meridionally extended fringe of colder (warmer) water extending as far as 250 km from the coast at 15 degrees S. In the Piura region, the intraseasonal covariability pattern is represented by two modes, one relevant to the direct Ekman dynamics and the other one associated with the remote forcing of intraseasonal oceanic Kelvin wave. Two regimes of variability are evidenced. A low-period regime (10-25 days) is the signature of Ekman transport/pumping dynamics and is remotely forced by the migratory atmospheric disturbances across the southeastern Pacific anticyclone. A high-period regime (35-60 day band) is associated with the combined forcing of oceanic equatorial Kelvin waves and migratory atmospheric disturbances in the midlatitudes. In particular, the modes of covariability exhibit a prominent similar to 50 day period energy peak. It is shown that this period arises from the impact of the first two baroclinic modes Kelvin wave, with the second baroclinic mode Kelvin wave being more influential on the Piura region.
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