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Rain-driven Turbulence in the Upper Meter of the Ocean
[22-May-2017] Drushka, K., Clark, D., Asher, W., Chickadel, C., Jessup, A., Thomson, J., and Thompson, E.
Presented at the Global Ocean Salinity and the Water Cycle Workshop
Rain falling on the ocean produces buoyant surface layers of relatively fresh, cool water that are subsequently mixed laterally and vertically into the water column. Because it is difficult to make measurements near the sea surface, relatively little is known about the dynamics of this mixing and as a result, our understanding of how rainfall affects upper ocean salinity is limited. Here, we consider the response of the upper meter of the ocean using three months of measurements collected during the Friday Harbor Rain Experiment. Acoustic Doppler velocimeters, CTDs, and a suite of meteorological sensors were deployed over winter 2015-16 with the objective of quantifying the impacts of rainfall on the upper ocean. We examine how wind speed, rain rate and raindrop size, and background ocean conditions affect near-surface dynamics. In the upper few centimeters of the ocean, turbulence is dominated by wind forcing. Below 20 cm depth the impacts of rainfall are pronounced, with turbulent dissipation rate two orders of magnitude greater in in moderate rains compared to non-rain conditions. These observations are compared to outputs from a 1-d model, and the implications for parameterizations of near-surface turbulent mixing are discussed.

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