Transport and Lagrangian Statistics in Rotating Stratified Turbulence

Abstract:

Transport plays a crucial role in geophysical flows, both in the
atmosphere and in the ocean. Transport in such flows is ultimately
controlled by small-scale turbulence, although the large scales are
in geostrophic balance between pressure gradient, gravity and Coriolis
forces. As a result of the seemingly random nature of the flow, single
particles are dispersed by the flow and on time scales significantly
longer than the eddy turn-over time, they undergo a diffusive motion
whose diffusion coefficient is the integral of the velocity correlation
function. On intermediate time scales, in homogeneous, isotropic turbuilence
(HIT) the separation between particle pairs has been argued to grow with
time according to the Richardson law: <(Δ x)²(t)> ~ t³, with a
proportionality constant that depends on the initial particle
separation. The description of the phenomena associated with
the dispersion of single particles, or of particle pairs, ultimately
rests on relatively simple statistical properties of the flow
velocity transporting the particles, in particular on its temporal
correlation function. In this work, we investigate particle dispersion
in the anisotropic case of rotating stratified turbulence examining whether
the dependence on initial particle separation differs from HIT,
particularly in the presence of an inverse cascade.