Sea surface freshening inferred from SMOS and ARGO salinity: impact of rain
Résumé
The sea surface salinity (SSS) measured from space by the Soil Moisture and OceanSalinity (SMOS) mission has recently been revisited by the European Space Agencyfirst campaign reprocessing. We show that, with respect to the previous version, biases close to land and ice greatly decrease. The accuracy of SMOS SSS averaged over 105days 100×100 km2in the open ocean and estimated by comparison to ARGO SSS is on the order of 0.3–0.4 in tropical and subtropical regions and 0.5 in a cold region. Themean SSS−0.1 bias observed in the Tropical Pacific Ocean between 5◦N and 15◦N, relatively to other regions, is suppressed when SMOS rainy events, as detected on SSM/Is rain rates, are removed from the SMOS-ARGO comparisons. The SMOS fresh-10ening is linearly correlated to SSM/Is rain rate with a slope estimated to −0.14 mm−1 h,after correction for rain atmospheric contribution. This tendency is the signature of thetemporal SSS variability between the time of SMOS and ARGO measurements linked to rain variability and of the vertical salinity stratification between the first centimeter of the sea surface layer sampled by SMOS and the 5 m depth sampled by ARGO. However, given that the whole set of collocations includes situations with rainy ARGO measurements collocated with non rainy SMOS measurements, the mean−0.1 bias and the negative skewness of the statistical distribution of SMOS minus ARGO SSS difference are very likely the mean signature of the vertical salinity stratification. In the future, the analysis of ongoing in situ salinity measurements in the top 50 cm of 20the sea surface and of Aquarius satellite SSS are expected to provide complementary information about the sea surface salinity stratification.
Origine : Publication financée par une institution
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