Geostrophic Adjustment of an Isolated Diapycnal Mixing Event and Its Implications for Small-Scale Lateral Dispersion

In this first of two companion papers, the time-dependent relaxation of an isolated diapycnal mixing event is examined in detail by means of numerical simulations, with an emphasis on the energy budget, particle displacements, and their implications for submesoscale oceanic lateral dispersion. The adjustment and dispersion characteristics are examined as a function of the lateral extent of the event L relative to the Rossby radius of deformation R. The strongest circulations and horizontal displacements occur in the regime R/L ≈ O(1). For short times, less than an inertial period, horizontal displacements are radial. Once the adjustment is completed, displacements become primarily azimuthal and continue to stir fluid over several to tens of inertial periods. The cumulative effect of many such events in terms of the effective lateral dispersion that they induce is examined in the companion paper.