Positive Salinity Gradients at the Ocean Surface Formed by Evaporation Measured During STRASSE-2012
[27-Feb-2014] Asher, W.E., Jessup, A.T., and Clark, D.
Presented at the 2014 Ocean Sciences Meeting
Salinity gradients in the top few meters of the ocean surface can exist due to precipitation or evaporation. If present, they will complicate comparing salinity measured by ARGO drifters at typical depths of five meters to salinities retrieved using L-band microwave radiometers such as Aquarius and SMOS at depths on order of 0.01 m. Therefore, understanding the spatial scales and temporal persistence of these gradients, and the conditions under which they form, will be important in calibrating satellite measurements of sea surface salinity. A towed, surface-following profiler was deployed from the N/O Thalassa
during the 2012 Subtropical Atlantic Surface Salinity Experiment (STRASSE). The profiler measured temperature and conductivity in the surface ocean at depths of 10 cm, 20 cm, 50 cm, and 100 cm. The measurements show that positive salinity gradients are commonly present at the ocean surface for wind speeds less than 4 m s-1 under conditions when the average daily insolation exceeds 300 W m-2. A semi-empirical model is presented that simulates the main features of these salinity gradients. The model results and the field data suggest that although these salinity gradients are common at the ocean surface and can extend for many kilometers, their magnitude is not large enough to significantly affect microwave radiometric measurements of salinity.