Meetings: Documents

A Study of the Interaction Between Salinity, Rain and Wind
[28-Aug-2018] Jacob, M.M., Jones, L., Drushka, K., and Asher, W.
Presented at the 2018 Ocean Salinity Science Team and Salinity Continuity Processing Meeting
When rain falls over the ocean, it produces a vertical salinity profile that is fresher at the surface. This fresh water will be mixed downward by turbulent diffusion through gravity waves and the wind stress (Boutin et. al., 2014), which dissipates over a few hours until the upper layer (1-5 m depth) becomes well mixed. Therefore, there will be a transient bias between the bulk salinity, measured by in situ instruments, and the satellite-measured SSS (representative of the first cm of the ocean depth).
Based on observations of Aquarius (AQ) SSS under rain conditions, a rain impact model (RIM) was developed to estimate the change in SSS due to the accumulation of precipitation previous to the time of the satellite observation (Santos-Garcia, et. al., 2014). RIM uses ocean surface salinities, from the HYCOM (Hybrid Coordinate Ocean Model) and the NOAA global rainfall product CMORPH, to model transient changes in the near-surface salinity profile. Also, the RIM analysis has been applied to SMOS (Soil Moisture and Ocean Salinity) and SMAP (Soil Moisture Active Passive), with similar results observed.
The original version of RIM, a 1D diffusion model, neglects the effects of wind and wave mixing. However, it was shown the mechanical mixing of the ocean caused by wind and waves rapidly reduces the salinity stratification caused by rain (Drushka, et. al., 2016). Also, previous results using RIM (Santos-Garcia, et. al., 2016), in the presence of moderate/high wind speeds, show that the model overestimates the rain effect on SSS. To address this issue, previous work (RIM-2) focused on the parameterization of the effects of wind on the vertical diffusivity (Kz). Preliminary results did not show great improvement, probably due to the fact that the mixing depth (d0) also varies with wind speed. Therefore, this paper will account for the wind speed effects on both Kz and d0 that result in a new version of the model, RIM-3. Results will be presented that compare RIM and RIM-3 at different depths for several parametrizations. Also, comparisons, between RIM-3 at depths of several meters with measurements from in situ salinity instruments, will be presented.
Boutin, J., N. Martin, G. Reverdin, S. Morisset, X. Yin, L. Centurioni, and N. Reul (2014). Sea surface salinity under rain cells: SMOS satellite and in situ drifters observations, Journal of Geophysical Res. Oceans, 119(8), 5533-5545, doi:10.1002/2014JC010070. Santos-Garcia, A., M.M. Jacob, W.L. Jones, W.E. Asher, Y. Hejazin, H. Ebrahimi, and M. Rabolli (2014). Investigation of rain effects on Aquarius Sea Surface Salinity measurements, Journal of Geophysical Res. Oceans, 119, 7605-7624, doi:10.1002/2014JC010137.
Drushka, K., W.E. Asher, B. Ward, and K. Wallaby (2016). Understanding the formation and evolution of rainformed fresh lenses at the ocean surface, J. Geophys. Res. Oceans, 121(4), 2169-9291, 10.1002/2015JC011527.
Santos-Garcia, A., M.M. Jacob, and W.L. Jones (2016). SMOS Near-Surface Salinity Stratification under Rainy Conditions, IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 9(6), 2493-2499, doi: 10.1109/JSTARS.2016.2527038.

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