Drifter spectra and diffusivities
The relationships between Eulerian and Lagrangian (or drifter) diffusivities and spectra are explored in detail using the Lagrangian correlation predictor due to Corrsin (1959). The analysis, applicable to homogeneous, isotropic velocity fields shows that an important dimensionless parameter in the Euler-Lagrange transformations is the ratio α of Eulerian integral TE to advective Ta time scales. It is found that the diffusivity may be approximated to within 10% by the function q2TE (q2 + α2)−1/2 where 2 is the mean-square velocity component and q ≃ 0.63. This result is found to be insensitive to the shape of the Eulerian spectra. It is also shown that a (wavenumber)−3 energy spectrum may be identified in Lagrangian frequency space by a corresponding (frequency)−3 spectrum. The relationships between drifter and fixed current meter spectra and time-scales are also explored. It is suggested that for regions of strong mean flow, U > , that the diffusivity might well be approximated by q √3 UTu where Tu is the mooring velocity time scale.
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Document Type: Research Article
Publication date: 1985-02-01
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