Study of Spatial Spectra of Horizontal Turbulence in the Ocean Using Drifter Data

Abstract

The statistics of a pair of Lagrangian particles offer, in principle, a possibility to estimate the structure functions of velocity, then the spatial autocorrelations, and finally the spatial spectra. On the basis of this strategy, the authors have developed an approach to estimate spatial spectra of mesoscale horizontal turbulence in the ocean using data of satellite-tracked drifters. The approach was applied to the data of 19 drifters deployed in the California Current System in 1993. It was found that the shape of both those spectra and this spectra calculated using drifterborne longitudinal and transverse correlations estimated by other authors are qualitatively in good accordance with theoretical predictions for 2D isotropic nondivergent turbulent flow. To relate obtained spectra to some physical parameters, kinematic stochastic models were developed that consisted of a population of randomly spaced, 2D axisymmetric eddies of a given shape. Numerical experiments with different eddy shapes showed that the model spectra obey a self-similarity; that is, at a given eddy shape they depend on the variance of stochastic process and a length scale of the eddy only. A model with the exponential eddy shape was found to fit drifterborne spectra better than other models. The best agreement between the drifterborne and model spectra was achieved when the radius of an exponentially shaped model eddy was taken equal to the internal Rossby radius.