Review of recent evaluation of sea surface salinity with satellite estimates in the tropical Indian Ocean

Aquarius is a mission that aims to measure the sea surface salinity (SSS) from space to provide the global salinity for climate studies. Accurate estimation of SSS is useful for the hydrological cycle, oceanographic processes, and climate. Recently, the new version (V4) of Aquarius data releases with the improving of the quality of the data and achieving the mission accuracy requirement globally on monthly scale. The results of the comparison of recently released Aquarius V4 with its preceding version’s (version 3; V3) data on a monthly time scale from 2012 to 2014 periods are highlighted. Spatial distribution of mean SSS shows that both products capture the SSS variability very well. Aquarius V4 SSS showed a minor improvement over the Aquarius V3 SSS with less root-mean-square error over the central and eastern equatorial Indian Ocean and part of Bay of Bengal. This is the region where both versions have a large difference in mean SSS. The frequency distribution is also improved in Aquarius V4 compared to Aquarius V3 average over the different regions. However, both the versions overestimate/underestimate the frequency of low/high salinity values. We also used the ocean reanalysis data to show the improvement in Aquarius V4 using the triple-point analysis method.