Satellite observations of sea surface salinity (SSS) have been validated in a number of instances using different forms of in situ data, including Argo floats, moorings and gridded in situ products. Since one of the most energetic timescales of variability of SSS is the seasonal, it is important to know if satellites and in situ gridded products are observing the seasonal variability correctly. In this study we validate the seasonal SSS from satellite and in situ products using observations from moorings in the global tropical moored buoy array. We utilize 6 different satellite products, and two different in situ gridded products. For each product we have computed seasonal harmonics, including amplitude, phase and fraction of variance (R2). These quantities are mapped for each product and for the moorings. We also do comparisons of amplitude, phase and R2 between moorings and all the satellite and in situ products. Taking the mooring observations as ground truth, we find general good agreement between them and the satellite and in situ products, with near zero bias in phase and amplitude and small root mean square differences. Tables are presented with these quantities for each product quantifying the degree of agreement.

Seasonal cycle is the largest source of variability for sea surface salinity (SSS) and has a significant influence on the upper-ocean stratification and water-mass formation. The advent of the Argo profiling floats and L-band passive microwave remote sensing in the past one and half decade has significantly improved the sampling of seasonal variations of SSS over the global ocean. Assessing the seasonality of SSS using these recent measurements is important for understanding its relationships with freshwater forcing and ocean dynamics as well as for identifying potential limitations of the SSS observing system. Here we utilize a suite of SSS products from recent satellite and in-situ platforms to revisit seasonal variations of SSS under different freshwater forcing conditions. The result shows that, although the annual harmonic is the most characteristic feature of the seasonal cycle, the semiannual harmonic is not negligible, especially in regions influenced by monsoon and major rivers. The annual and semiannual harmonics account for 70–80 % and 10–16 % of the total observed variance respectively, which together drive the SSS seasonality. The range of seasonal SSS is approximately ±0.05 practical salinity scale (pss) in the subtropical SSS maximum regions, but greater than ±0.25 pss in the tropical SSS minimum regions. However, the seasonal variations of satellite SSS in the 20-40°N latitude range showed erroneous annual and semiannual phases compared with in situ products, the cause of which needs further examination.