A simulation of a turbulent mesoscale current by eddy and current superposition to predict sound velocity variations

Abstract

Ocean mesoscale currents display large-scale turbulence, clearly evident in remotely sensed imagery and in situ XBT casts. Deducing water velocity from remotely sensed data is a topic of ongoing research. The relationship of geostrophic water velocity and the acoustically relevant water column parameters has been expressed in the quasigeostrophic equation. Two general solutions of this equation, the uniform current [J. G. Watson, W. L. Siegmann, and M. J. Jacobson, J. Acoust. Soc. Am. 60, 355–364 (1976)] and the symmetrical eddy [R. F. Henrick, W. L. Siegmann, and M. J. Jacobson, J. Acoust. Soc. Am. 62, 860–870 (1977)], are analyzed and combined into one dynamical model. A scheme to reduce the three-dimensional temperature and velocity distributions of a turbulent current to simple eddies superimposed on a current is presented. The dynamical model is then used to predict the variations in sound speed across the current. A simulation of the North Pacific Current is given and the predicted sound velocity profiles are compared to data collected from the region [W. J. Emery et al., J. Acoust. Soc. Am. 66, 831–841 (1979)].