Rain-Induced Ocean Surface Salinity Gradients
[16-Apr-2013] Asher, W., Jessup, A., Branch, R., and Clark, D.
Presented at the 2013 SMOS-Aquarius Science Workshop
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 SMOS and Aquarius, whose measurement depths are 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 understanding sea surface salinity maps provided by SMOS and Aquarius. Salinity gradients in the top two meters were also measured using a towed profiler that was capable of resolving gradients on the same vertical scale as the radiometric measurement depth. Measurements of near surface salinity profiles using a towed profiler were made in December, 2011 aboard the R/V Kilo Moana and in 2012 during STRASSE have shown that both positive (i.e., salinity decreasing with increasing depth) and negative (i.e., salinity increasing with depth) gradients can form at the ocean surface. The data are used to understand how environmental forcing leads to the formation and collapse of these gradients. From this it is possible to estimate the likelihood that gradients with large enough change in salinity and of sufficient spatial scale and lifetime to affect microwave radiometric measurements of salinity will form at the ocean surface. Initial results show that precipitation produces gradients in near-surface salinity with horizontal spatial scales comparable to the footprint of Aquarius and that the magnitude of these gradients can be significant in terms of the overall accuracy of the satellite.