Nonlinear Processes in Oceanic and Atmospheric Flows


The evolution of tracer patches

Author: Daniel A Birch, Scripps Institution of Oceanography.

Names and affiliation of other authors:
William R. Young, Scripps Institution of Oceanography

Oral or poster: Oral presentation

Downloadable talk file:

The evolution of tracer patches

(Birch.NLOA.2008.pdf, 560927 bytes)

We use explicit solutions of the advection-diffusion equation to
examine the evolution of a patch of a passive tracer subject to
vertical shear, horizontal strain, and diffusion. We are especially
interested in the evolution of the patch's vertical thickness,
horizontal extent, slope, and intensity. In the case of steady shear
with no strain, the patch forms a layer with a minimum layer thickness
determined by the shear, vertical diffusivity, and the initial
horizontal scale of the patch. The initial thickness of the patch is
irrelevent. Furthermore, the patch's thickness, extent, and intensity
all evolve algebraically in time. The addition of non-zero horizontal
strain causes the evolution of the patch properties to become
exponential in time. Furthermore, steady horizontal strain causes the
patch to tend towards a steady-state vertical thickness. This is in
contrast to the case with zero strain, in which the patch thickness
grows diffusively with time. Finally, we supplement the steady-flow
models with Monte Carlo simulations of time-dependent flow models.

*Satellite images from NASA and ESA

Nonlinear Processes in Oceanic and Atmospheric Flows. July 2-4, 2008. Castro Urdiales, Cantabria, Spain.