Seven Years of SMOS Sea Surface Salinity at High Latitudes: Variability in Arctic and Sub-Arctic Regions

Abstract

This paper aims to present and assess the quality of seven years (2011–2017) of 25 km nine-day Soil Moisture and Ocean Salinity (SMOS) Sea Surface Salinity (SSS) objectively analyzed maps in the Arctic and sub-Arctic oceans ( 50 ∘ N– 90 ∘ N). The SMOS SSS maps presented in this work are an improved version of the preliminary three-year dataset generated and freely distributed by the Barcelona Expert Center. In this new version, a time-dependent bias correction has been applied to mitigate the seasonal bias that affected the previous SSS maps. An extensive database of in situ data (Argo floats and thermosalinograph measurements) has been used for assessing the accuracy of this product. The standard deviation of the difference between the new SMOS SSS maps and Argo SSS ranges from 0.25 and 0.35. The major features of the inter-annual SSS variations observed by the thermosalinographs are also captured by the SMOS SSS maps. However, the validation in some regions of the Arctic Ocean has not been feasible because of the lack of in situ data. In those regions, qualitative comparisons with SSS provided by models and the remotely sensed SSS provided by Aquarius and SMAP have been performed. Despite the differences between SMOS and SMAP, both datasets show consistent SSS variations with respect to the model and the river discharge in situ data, but present a larger dynamic range than that of the model. This result suggests that, in those regions, the use of the remotely sensed SSS may help to improve the models.

Evaluation of Arctic Ocean surface salinities from the Soil Moisture and Ocean Salinity (SMOS) mission against a regional reanalysis and in situ data

“…With respect to its previous version, a systematic bias in the retrieved salinity is corrected by computing the SMOS climatology (the most probable value for a given lat-long, incidence angle and across-swath distance), which is substituted by a reference value from WOA13. In addition, a temporal bias correction has been refined in this version using near-surface Argo salinity to compute regional averages (see the details in Olmedo et al, 2018).…”

“…SSS is known to impact the oceanic upper mixing significantly (Latif et al, 2000;de Boyer Montegut et al, 2004;Maes et al, 2006;Furue et al, 2018) via its effect on the surface layer density (Johnson et al, 2012). The SSS also affects the decadal variability of hydrography in the upper waters of the North Atlantic (Reverdin et al, 1997). Using a coupled atmosphere-ocean model and an observed SSS climatology dataset, Mignot and Frankignoul (2003) attributed the interannual variability of the Atlantic SSS to two factors: anomalous Ekman advection and the freshwater flux.…”

“…These two SMOS products have successfully resolved the Agulhas salinity front (D'Addezio et al, 2016) and proven useful for estimating precipitation (Supply et al, 2018). The work of Olmedo et al (2018) quantitatively evaluates the accuracy of the SMOS Arctic and sub-Arctic SSS to less than 0.35 psu, but this evaluation against Argo data was limited by the lack of data in the Arctic proper. The present study thus investigates the accuracy of these two L3 SSS products from SMOS in the Arctic Ocean.…”

Surface waters properties in the Laptev and the East-Siberian Seas in summer 2018 from in situ and satellite data

“…However, the precision degrades in cold water as the sensitivity of L-band radiometer signal to SSS decreases when SST decreases, even though this effect on temporally averaged maps is partly compensated by the increased number of satellite measurements at high latitude. A possibility of using SSS estimates in cold regions derived from L-Band radiometry was, however, demonstrated recently by several working groups (Tang et al (2018), Grodsky et al (2018), Olmedo et al (2018). However SMAP CAP/JPL or SMOS BEC L3 products are spatially averaged from 60 km to more than 100 km.…”

Correction: Olmedo, E., et al. Seven Years of SMOS Sea Surface Salinity at High Latitudes: Variability in Arctic and Sub-Arctic Regions. Remote Sensing 2018, 10, 1772

“…The authors wish to make the following corrections to this paper [1]: The authors have detected an error in the program which computes the statistics with ARGO. The definition of some domains were wrong.…”