Abstract
We study the statistics of wind-driven open ocean currents. Using the Ekman layer model for the integrated currents, we investigate analytically and numerically the relationship between the wind-stress distribution and its temporal correlations and the statistics of the open ocean currents. We found that temporally long-range correlated winds result in currents whose statistics is proportional to the wind-stress statistics. On the other hand, short-range correlated winds lead to Gaussian distributions of the current components, regardless of the stationary distribution of the winds, and therefore to a Rayleigh distribution of the current amplitude, if the wind stress is isotropic. We found that the second moment of the current speed exhibits a maximum as a function of the correlation time of the wind stress for a non-zero Coriolis parameter. The results were validated using an oceanic general circulation model.
Highlights
Ocean currents are generated by local and remote forces and factors, including winds, tides, buoyancy fluxes and various types of waves
Currently there is no accepted theory explaining the observed statistics of surface ocean currents
We show that the distribution of wind-driven ocean currents strongly depends on the temporal correlations of the wind–when the wind exhibits long-range temporal correlations, the ocean current statistics is proportional to the wind-stress statistics, while for short-range correlations of the wind, the different components of the current vector follow Gaussian distributions
Summary
Ocean currents are generated by local and remote forces and factors, including winds, tides, buoyancy fluxes and various types of waves. We propose a simple physical theory for the distribution of wind-driven ocean currents and its relation to the spatially variable temporal correlations of the wind (see Fig. 1). The study of wind-driven ocean currents goes back more than 100 years, to the time when Ekman [9] proposed his classical simple model to explain the effect of the Earth’s rotation on upper ocean currents. His model predicted that the depth-integrated current vector is perpendicular to the wind vector, a prediction that was largely proven by observations. We use Ekman’s model [9] to study the statistics of wind-driven ocean currents.
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