Observations and Modeling of Rain-Induced Near Surface Salinity Anomalies
[28-Nov-2014] Asher, W.
Presented at the 2014 Ocean Salinity Science and Salinity Remote Sensing Workshop
Vertical salinity gradients in the top few meters of the ocean surface can exist due to the freshwater input from rain. If present, they will complicate comparing salinity measured by ARGO drifters at typical depths of a few 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 the frequency of occurrence of these vertical 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 near-surface ocean caused by rain were measured using a towed profiler that measured vertical gradients in the top two meters of the ocean with a minimum measurement depth of 0.1 m. These measurements were made in December, 2011 aboard the R/V Kilo Moana. In addition, an underway salinity profiling system was installed on the R/V Thomas G. Thompson. This measured near-surface salinity at depths of 1 m and 2 m. Both the towed profiler and the underway system found the occurrence of negative salinity anomalies (i.e., salinity decreasing towards the surface) was correlated with the presence of rain. The results show that precipitation produces vertical 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. Numerical studies of the ocean surface mixed layer show that the formation and evolution of the observed salinity anomalies are consistent with a one-dimensional turbulence diffusion model.