Variability and Uncertainty in Satellite Sea-surface Salinity Observations

When employing satellite sea-surface salinity (SSS) observations in studies of observed and modeled ocean variability and change, assessments must consider the variability and uncertainty contained within the satellite SSS data that may or may not reflect physical processes. Coherent temporal and spatial structures exists in the differences between the ascending (south to north) and descending (north to south) nodes of both NASA’s Aquarius mission and ESA’s Soil Moisture – Ocean Salinity (SMOS) mission, introducing non-physical variability into the data. When examining “simultaneous” match-ups of both Aquarius and SMOS satellite observations with Argo float in situ observations (triple match-up), the Aquarius and SMOS data exhibit different temporal and spatial variabilities with respect to the in situ data, as well as with respect to each other. While physical differences will exist between the skin salinity (approximately 1cm) observed by the satellites and the near-surface salinity (approximately 5 m) observed by Argo floats, when using satellite SSS observations, non-physical variability may intrude into assessments of ocean salinity variability.