Isopycnal dispersion in NATRE

Abstract

Finescale velocity and density fluctuations consist of both internal waves and vorticity-containing perturbations (vortical modes). A recent decomposition of observations obtained as part of the North Atlantic Tracer Release Experiment (NATRE) permits one to investigate isopycnal stirring associated with vortical modes. This stirring is treated here as a relative dispersion problem in the context of 2D turbulence. Isopycnal diffusivities attain values on the order of 1 m2 s-1 after an initial transient of 5-10 days. After 2 weeks, a patch of tracer with initial radius of 25 m is predicted to have evolved into a convoluted web having an rms radius of 2-4 km. These estimates agree with observations of the evolution of an anthropogenic tracer in NATRE. © 2004 Meteorological Society.