Chapter 16 Interannual and Seasonal Variability of the Tropical Atlantic ocean depicted by Sixteen years of Sea-Surface Temperature and wind stress

Abstract

Abstract Monthly fields of sea-surface temperature and wind stress for the tropical Atlantic are carefully established for January 1964 to December 1979. The availability of these gridded data sets permits a few simple measures of the seasonal and interannual variability of the tropical Atlantic. Throughout most of the basin the amplitude of seasonal SST variability is greater than the amplitude of monthly SST anomalies. Interannual fluctuations of SST are largest in areas of large seasonal SST variability such as coastal and equatorial upwelling zones. In these regions monthly SST anomalies may reach 1°—2°C. As opposed to SST, the largest year-to-year changes in wind stress do not necessarily coincide with the locations of the largest seasonal cycles. The amplitude of monthly wind stress anomalies is greater than the amplitude of the seasonal cycle except in the vicinity of the ITCZ. The range of monthly wind stress anomalies along the equator and eastern boundary, expressed in units of wind speed squared, is 10–20m 2 s −2 . Of particular note are the differing phase relationships with the seasonal cycle for the interannual fluctuations of SST and wind stress within the upwelling zones of the Northern and Southern Hemispheres. Moreover, sample time series of SST and wind stress are characterized, at times, by anomalous events persisting for more than one year. This evidence is suggestive of anomalous conditions in the tropical Atlantic that are not the result of a simple phase shift or change in amplitude of the seasonal cycle.