Sea Surface Salinity (SSS) is an Essential Ocean and Climate Variable, which is increasingly used as part of climate studies. SSS measurements are available from three satellite missions, SMOS, Aquarius and SMAP, each with very different instrument features leading to specific measurement characteristics. The Climate Change Initiative Salinity project (CCI+SSS) aims to produce SSS Climate Data Record (CDR) to include satellite measurements, based on well-established user needs. To generate a homogeneous CDR, instrumental differences are carefully controlled by analysing SSS discrepancies, then adjusted based on in-depth analysis of the measurements themselves together with independent reference data. However, no spatial smoothing or temporal relaxation to reference data is applied in order to maintain the variability contained in the original data set. SSS CCI fields are well suited for monitoring weekly to interannual variability from the ocean basin scale to the large mesoscale. Thus, they depict that over the 2010-2019 decade, seasonal have varied greatly from year to year, sometimes by more than +/-0.4 over large regions. When monthly SSS CCI are compared with in situ Argo salinities, the robust standard deviation of their difference, at global scale, is 0.15, while r2 is 0.97. This high level of performance highlights the benefit of the SSS CCI merging approach compared to individual satellite SSS fields alone. The correlation with independent ship SSS (r2>0.9) further highlights the excellent performance of the data set. SSS CCI data are freely available and will be updated and extended in the future as more satellite data become available.

The Arctic Ocean contains only a 1% of the world’s ocean water, but the rivers that flow out into it account for the 10% of the volume world’s rivers freshwater. The upper layer of fresher water facilitates the creation of sea ice and plays an important role in the position of the jet stream and storms over the northern hemisphere [ISBN, 978-82-7971-097-4]. Remote sensing measurements are of special importance in the Arctic since in situ data is very scarce there. SMOS and SMAP are currently providing sea surface salinity (SSS) measures, but only the product provided by Barcelona Expert Center (BEC) is a dedicated product for the Arctic region. The product that we present in this work is an improvement of the BEC Arctic v2.0. The new version 3.0 has as the primary objective the describing better the river discharges. The spatial grid used is WGS84/NSIDC EASE-Grid 2.0 North for the all stages of the processing chain. This procedure avoids spatial interpolation, favoring the definition of river mouths. The salinity retrieval is based on the Debiased non-bayesian method [doi:10.1016/j.rse.2017.02.023] and similarly to what is done in the processing of altimetric data, SMOS salinity is corrected using a reference calculated from the own SMOS data for each latitude, longitude, pass orientation and antenna measuring position. Arctic v3.0 differs from current method [doi:10.3390/rs10111772] in two important points: the reference is computed for brightness temperature instead of SSS and the antenna has been divided in a more homogeneous grid. Other improvements concern to data filtering and propagation of the radiometric errors to SSS. All these improvements provide level 3 maps less noisy, increasing the effective resolution of salinity gradients. Freshwater gradients are much better resolved than in previous version (Fig. 1). Comparison with JPL SMAP product is also planned as a first step to generate a combined product. This work is funded by ESA Arctic + project and also includes the assimilation of the resulting SSS product in the ocean-sea ice data assimilation system TOPAZ as the next version TOPAZ5. A preliminary study [doi:10.5194/os-2018-163] has been performed concluding that BEC product could be a good candidate to be assimilated by TOPAZ. Moreover, some preliminary tests with a pre-release v3.0 version will start shortly.