Nonlinear Processes in Oceanic and Atmospheric Flows


The vortex merger rate in decaying 2D turbulence

Author: Joseph H. LaCasce, University of Oslo.

Names and affiliation of other authors:

Oral or poster: Oral presentation

Downloadable talk file:

The vortex merger rate in decaying 2-D turbulence

(mergetalk6.pdf, 3183354 bytes)

New numerical simulations of decaying two-dimensional turbulence are
examined, with a focus on the statistics of the coherent vortices.
The number of vortices decays as a power law, as in previous studies,
but the rate varies between experiments. While the rate is not
significantly affected by changes in the initial conditions, it does
depend on the choice of small scale dissipation. In contrast, the
vortex dispersion rate is approximately the same in all the
experiments. Assuming energy conservation, the decay rate can be
determined from the dispersion rate. The prediction agrees well with
the rate observed in the least dissipative experiments. In the more
dissipative experiments, the decay rate is greater because the
dissipation increases lateral extent of the vortices and hence their
collision cross section. In such cases, the density decay rate can be
predicted from a scaling relation involving the collision time, given
the observed growth rate of the mean vortex area.

*Satellite images from NASA and ESA

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