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Study Improves Drifter-Based Estimates of Near-Surface Ocean Currents

July 10, 2019

Using 40 years of observations from the NOAA’s Global Drifter Program Array, the authors depict the annual mean speed of ocean currents at 15 meters depth. The vectors highlight the general direction of the large-scale circulation. Image provided by Lucas Laurindo, University of Miami Rosenstiel School of Marine and Atmospheric Science.

Scientists developed a new approach to improve near-surface (15 meters depth) ocean circulation estimations derived from drogued and undrogued drifters (drogues extend below the surface, providing stability) used in the NOAA Global Drifter Program. The proposed new estimation method improves the definition of smaller-scale circulation details relative to traditional methods. Additionally, the team compared the new approach to altimeter-derived velocity data (subsampled at the drifter locations), which revealed that traditional methods likely underestimate the statistical uncertainty of the mean current estimates by a factor of two. The comparison also showed that the corrected slip of undrogued drifters produces velocity measures similar to drogued drifters, doubling the amount of usable data. These combined operations recovered large-scale circulation features that previous drifter-based assessments had not defined well (core speeds for Florida/Gulf Stream Currents were 50% larger) and resolved coherent structures at mesoscale ranges whose visualization was only possible by inferring surface velocities from satellite observations.

The researchers published their findings in Deep Sea Research Part I: Oceanographic Research Papers: An improved near-surface velocity climatology for the global ocean from drifter observations.

“A statistical description of the surface ocean circulation is useful for a variety of applications,” explained study author Lucas Laurindo. “In addition to its value for academic studies, circulation estimates can be used to predict the transport of fish larvae and pollutants such as oil, plastic, and marine debris. In conjunction with satellite observations, it can also help define the most fuel-efficient ship routes across the oceans and serve as a support tool for search-and-rescue operations.”

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