Horizontal mixing in the Atlantic Equatorial Undercurrent estimated from drifting buoy clusters

Publisher Website
Google Scholar
Abstract
During 1978 and 1979, four experiments with clusters of 6 to 10 drifting buoys were carried out in the Atlantic Equatorial Undercurrent. The measurements were intended to estimate horizontal mixing and its possible contribution to the salt loss of the high‐salinity core related to the Equatorial Undercurrent. The buoys were drogued at the estimated depth of the salinity core of 70 m to 90 m. The diameters of the spreading clusters ranged from 3 to 10 km. Each experiment was maintained for about 2 days. During this period the buoys were tracked by radar from a nearby operating research vessel. From the observed tracks, horizontal turbulent mixing coefficients were deduced. The results show a dependence on the horizontal scale of l1.43. This is not significantly different from an expected l4/3 law. Using the obtained scale dependence, the observations are extrapolated to the scale of the salinity core of 150 km obtained from hydrographic observations, resulting in a turbulent mixing coefficient of 6.5 × 106 cm2 s−1. Combining these numbers with the horizontal gradients of the salinity core, one obtains a salt loss of 1.42 g s−1 cm−1, which amounts to 20% of the complete salt loss of 7.2 g s−1 cm−1 compiled by Katz et al. (1980).