The relevance of chaotic advection to stratospheric mixing and transport is
addressed in the context of (i) a numerical model of forced shallow-water
how on the sphere, and (ii) a middle-atmosphere general circulation model.
It is argued that chaotic advection applies to both these models if there i
s suitable large-scale spatial structure in the velocity field and if the v
elocity held is temporally quasi-regular. This spatial structure is manifes
ted in the form of "cat's eyes" in the surf zone. such as are commonly seen
in numerical simulations of Rossby wave critical layers; by analogy with t
he heteroclinic structure of a temporally aperiodic chaotic system the cat'
s eyes may be thought of as an "organizing structure" for mixing and transp
ort in the surf zone. When this organizing structure exists, Eulerian and L
agrangian autocorrelations of the velocity derivatives indicate that veloci
ty derivatives decorrelate more rapidly along particle trajectories than at
fixed spatial locations (i.e., the velocity field is temporally quasi-regu
lar). This phenomenon is referred to as Lagrangian random strain.