LAGRANGIAN ACCELERATIONS IN GEOSTROPHIC TURBULENCE

A distinctive property of Lagrangian accelerations in geostrophic turb ulence is that they are governed by the large and intermediate scales of the flow, both in time and space, so that the inertial part of the dynamics plays a much larger role than in three-dimensional turbulence where viscous effects are stronger. For the case of geostrophic turbu lence on a P-plane, three terms contribute to the Lagrangian accelerat ions: the ageostrophic pressure gradient which often is the largest te rm, a meridional acceleration due to the p-effect, and an acceleration due to horizontally divergent ageostrophic motions. Both their spectr al characteristics and patterns in physical space are studied in this paper. In particular the total accelerations field has an inertial spe ctrum slope which is identical to the geostrophic velocity field inert ial slope. The accelerations gradient tensor is shown to govern the to pology of quasigeostrophic stirring and transport properties. Its posi tive eigenvalues locate accurately the position of extrema of potentia l vorticity gradients. The three-dimensional distribution of tracer gr adients is such that the vertical distribution is entirely constrained by the horizontal one, while the reverse is not true. We make explici t analytically their dependence on the three-dimensional accelerations gradient.