Mixing in a Meandering Jet: A Markovian Approximation

Abstract

Mixing and transport in correspondence of a meandering jet are investigated. The large-scale flow field is a kinematically assigned streamfunction. Two basic mixing mechanisms are considered separately and in combination: deterministic chaotic advection induced by a time dependence of the flow, and turbulent diffusion described by means of a stochastic model for particle motion. Rather than looking at the details of particle trajectories, fluid exchange is studied in terms of Markovian approximations. The 2D physical space accessible to fluid particles is subdivided into regions characterized by different Lagrangian behavior. From the observed transitions between regions it is possible to derive a number of relevant quantities characterizing transport and mixing in the studied flow regime, such as residence times, meridional mixing, and correlation functions. These estimated quantities are compared to the corresponding ones resulting from the actual simulations. The outcome of the comparison suggests the possibility of describing in a satisfactory way at least some of the mixing properties of the system through the very simplified approach of a first-order Markovian approximation, whereas other properties exhibit memory patterns of higher order.