LARGE-SCALE HORIZONTAL MIXING IN PLANETARY-ATMOSPHERES

Some implications of chaotic advection for mixing of potential vorticity and chemical species by large-scale, two-dimensional, atmospheric flows are examined. It is argued that such mixing is important in the Earth's atmosphere and in those of the other rapidly rotating planets, but that the essential features of the mixing cannot be captured by an effective diffusivity. A means of identifying and characterizing chaotic mixing regions by examining patterns of spatial variation of finite-time estimates of the Lyapunov exponents is proposed, and tested on a number of idealized cases. Some preliminary results on application of the method to Northern Hemisphere atmospheric data are reported. The principal mixing zones, characteristic mixing time, and barriers to transport are identified.