Sea Surface Salinity Seasonal Variability in the Tropics from Satellites, Gridded In Situ Products and Mooring Observations

Abstract

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 time scales of variability of SSS is seasonal, it is important to know if satellites and gridded in situ products are observing the seasonal variability correctly. In this study we validate the seasonal SSS from satellite and gridded in situ products using observations from moorings in the global tropical moored buoy array. We utilize six different satellite products, and two different gridded in situ 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 gridded in situ products. Taking the mooring observations as ground truth, we find general good agreement between them and the satellite and gridded 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.

Revisiting the Global Patterns of Seasonal Cycle in Sea Surface Salinity

“…Interestingly, the R 2 values for in situ products are generally greater than those for satellite products although the harmonic amplitude patterns are all similar. A similar result was also obtained by Bingham et al (2021) in the tropics using mooring data as an in situ comparison. This is especially the case in the extratropical ocean where annual amplitudes in most areas are lower than 0.1 pss.…”

“…It is found that the R 2 values vary with the type of product. The R 2 values for annual harmonic are relatively lower in satellite products, at about 49%-58%, but are higher in in situ products, at about 66%-72% (Bingham et al, 2021). The R 2 values for the semiannual harmonic are more in a more narrow range, at about 15%-19% in all products.…”

“…The second measure is the F-statistic that tests whether the data product and the respective harmonic mode has the same variance. Following Bingham et al (2021), the F-statistic was calculated from R 2 using the equation…”

Sea Surface Salinity Short Term Variability in the Tropics

“…SSS in the tropics tends to be quite spiky, with many low outliers, (e.g. Bingham et al (2021), their Figure 2) Overly stringent quality control could eliminate many valid data points and alter the statistics of the record.…”

Matchup Characteristics of Sea Surface Salinity using a High-resolution Ocean Model

“…These may take the form of comparisons with gridded Argo products such as that of [5] or [6] ( [2,3,[7][8][9][10][11][12]). There may also be comparisons with individual observations such as floats, saildrones, thermosalinographs or moorings [8][9][10][13][14][15][16][17][18][19][20]. Comparisons may be done using satellite data at level 2 (L2) (e.g.…”