Satellite observed salinity distributions at high latitudes in the Northern Hemisphere: A comparison of four products

Global surface ocean salinity measurements have been available since the launch of SMOS in 2009 and coverage was further enhanced with the launch of Aquarius in 2011. In the polar regions where spatial and temporal changes in sea surface salinity (SSS) are deemed important, the data have not been as robustly validated because of the paucity of in situ measurements. This study presents a comparison of four SSS products in the ice-free Arctic region, three using Aquarius data and one using SMOS data. The accuracy of each product is assessed through comparative analysis with ship and other in situ measurements. Results indicate RMS errors ranging between 0.33 and 0.89 psu. Overall, the four products show generally good consistency in spatial distribution with the Atlantic side being more saline than the Pacific side. A good agreement between the ship and satellite measurements was also observed in the low salinity regions in the Arctic Ocean, where SSS in situ measurements are usually sparse, at the end of summer melt seasons. Some discrepancies including biases of about 1 psu between the products in spatial and temporal distribution are observed. These are due in part to differences in retrieval techniques, geophysical filtering, and sea ice and land masks. The monthly SSS retrievals in the Arctic from 2011 to 2015 showed variations (within similar to 1 psu) consistent with effects of sea ice seasonal cycles. This study indicates that spaceborne observations capture the seasonality and interannual variability of SSS in the Arctic with reasonably good accuracy. Plain Language Summary Salinity distribution in the Arctic is studied using four products from satellites Aquarius and SMOS. The results show general agreement of the four products with some biases associated with differences in retrieval, filtering and smoothing techniques. The products are consistent with in situ data with RMS error as low as 0.3 psu despite expected challenges in obtaining accurate salinities at cold temperatures. Overall, the spatial distribution as well as seasonal and interannual variations are consistent with expected changes in sea ice cover, precipitation and river runoff. The products show strong potential for many oceanographic applications and climate studies.