Abstract
The intraseasonal (IS) variability of the sea surface temperature (SST) in the Southwestern Atlantic Continental Shelf (SWACS, 45–33° S—70–50° W), and its relationship with that in the atmosphere, was studied for the austral warm season. SST satellite data (11-km resolution NOAA CoastWatch Program) and data of different atmospheric variables (Reanalysis1 NCEP/NCAR and ERA-Interim) were used. Data were filtered using a 10–90 day filter to isolate the IS variability. A Principal Component analysis was applied then to the filtered SST anomalies (SSTA) and the activity of the leading modes was described through the corresponding temporal series. The first three modes are significant. EOF1 (25.7% of variance) exhibits SSTA of opposite sign to the north/south of 42° S. EOF2 (9.0%) and EOF3 (5.1%) are related with centers of SSTA of opposite sign located off the Uruguayan coast and in the middle shelf. Composites of SSTA and of key atmospheric variables were made considering the days in which the main modes were active. They show that the SSTA described by the three modes are associated with distinctive regional sea level pressure anomalies that, in turn, seem to be related to atmospheric Rossby wave trains extending from the Australia area towards South America. The corresponding atmospheric wave sources vary depending on the mode. These results show, therefore, that the SSTA in the SWACS exhibit significant IS variability that is, in part, locally and remotely influenced by atmospheric anomalies oscillating on similar timescales. These ocean–atmosphere teleconnections could help to improve ocean predictability at those timescales in the future.
Highlights
Profound knowledge of sea surface temperature (SST) anomalies distribution over the continental shelves is essential to study oceanic processes such as frontal dynamics, upwelling and downwelling events, as well as eddies and plumes evolutions, which are important in biological applications
This work examines the main features of SST variability in the SWACS NACS in the intraseasonal time scale and assesses the relationship of this local variability with that observed in the Southwestern Atlantic Ocean (SWAO) and the Southern Hemisphere
Results are based on Empirical Orthogonal Functions (EOF) analysis of IS-filtered SST daily anomalies, where three main patterns were obtained, and compositions of oceanic and atmospheric variables were made considering the days in which those modes were active
Summary
Profound knowledge of sea surface temperature (SST) anomalies distribution over the continental shelves is essential to study oceanic processes such as frontal dynamics, upwelling and downwelling events, as well as eddies and plumes evolutions, which are important in biological applications. The knowledge of SST anomalies in the shelves is useful for climate monitoring and prediction, since they respond to a multiple-scale organization of atmospheric circulation anomalies occurring over distant parts of the globe, commonly called teleconnections. Climate teleconnections can exhibit variability on intraseasonal (IS) time scales, which are those between 10 and 100 days (Feldstein, 2003; Murakami, 1981; Wang et al, 2016). Whereas mid-latitudes are typically characterized by being energetic areas where eastward-moving atmospheric baroclinic waves dominate surface energy flux variations on synoptic timescales (3 to 10 days), quasi-stationary large-scale Rossby waves, blocking anticyclones as well as slowly moving cutoff lows contribute significantly to extratropical atmospheric variability on timescales longer than approximately 10 days (Alexander and Scott, 1997; Deser et al, 2010). The description and understanding of the atmospheric IS variability between 10
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