Spatial and temporal scales of satellite sea surface salinity variability in the Tropical Atlantic

Taking advantage of the different coverage of satellite-derived sea surface salinity (SSS), concurrent SMOS and Aquarius observations are used for the first time for the quantification of the spatial and temporal decorrelation scales of SSS in the Tropical Atlantic. Different 7-10 days composite SSS products from the two missions are used to examine any potential effects of varying resolution, bias corrections and averaging characteristics. Given the dominance of the seasonal cycle in SSS variability in the region, the scales are calculated both for the mean and anomaly SSS fields. With the seasonal cycle retained, homogeneous SSS variations are strongly anisotropic, with the longest zonal scales in the Tropics reaching over 2000 km and long temporal scales of up to 70-80 days, as seen by both SMOS and Aquarius. The longest meridional scales of over 1000 km occur in the South Atlantic (~10°-25°S), most discernible in Aquarius data. SSS variability has the longest persistence in time of up to 150-200 days at the Southern Sargasso Sea in the N.W. Atlantic. The removal of the seasonal cycle decreases noticeably the spatio-temporal scales over most of the basin. Overall, with the exception of differences in the S. Atlantic, there is good consistency between the spatio-temporal scales of SSS from the two satellites and different products, despite their individual calibration and resolution characteristics.

The new estimates of decorrelation scales of SSS improve our knowledge of the processes and mechanisms controlling the Tropical Atlantic SSS variability, and represent a powerful new investigative tool equally applicable to other regions, SSS products and other ocean geophysical properties. This work has also important applications for the evaluation of the impact of satellite SSS in assimilation systems, the development of optimally interpolated products, as well as the definition of appropriate validation procedures of the various satellite SSS products.