Evaluation of sea surface salinity observed by Aquarius

Sea surface salinity (SSS) data derived from the Aquarius mission were compared with global observation by Argo floats to evaluate the quality of the SSS and assess the error structure. The Aquarius SSSs agreed well with the Argo near-surface salinity with a root-mean-square (rms) difference of 0.42 psu (version 2.10.1 standard product). The residual of the salinity observation showed a significant correlation with the sea surface temperature (SST) and wind speed. SSS bias caused by inaccurate corrections for the galactic radiation was also discernible. Similar results were obtained for the Aquarius SSSs retrieved by the different algorithms. Aquarius monthly SSS averaged over 1° × 1° was also compared with outputs from a global ocean optimal interpolation system. The rms difference, calculated over 40°S-40°N, was 0.27 psu (version 2.10.1 standard product). The rms difference was reduced to 0.21 psu, which is very close to the goal of the Aquarius mission, for the product retrieved by an alternative algorithm (CAP version 25.1).