Physics – Fluid Dynamics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmng24a..01h&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #NG24A-01
Physics
Fluid Dynamics
4485 Self-Organization, 4490 Turbulence (3379, 4568, 7863), 4528 Fronts And Jets
Scientific paper
Flows exhibiting multiple zonal jets are ubiquitous in observations of the atmospheres of giant planets and in the oceans, as well as in laboratory experiments. Such systems share in common east-west velocity directions that alternate either with latitude or with depth and present a marked asymmetry, with the eastward jets being narrower and faster than the westward jets. Besides involving a considerable portion of the total kinetic energy, the existence of multiple zonal jets has profound implications on the transport and mixing of tracers by setting up barriers to meridional transport. Such barriers, which can be intermittent in space and time, partition the flow into well-mixed regions of distinct properties, a terrestrial example being the confinement of the atmospheric ozone hole by the barrier of the polar vortex jet. The viewpoint of basic nonlinear geophysical fluid dynamics has brought new insights and understanding on the characteristics of these concentrated large-scale flows. While the initial formation of zonal flows can occur through a variety of linear flow bifurcation processes or linear large-scale instability mechanisms, only nonlinear dynamics can explain their ultimate concentration into jet-like structures and their long-time evolution. Indeed, zonal jets can be viewed as coherent structures that spontaneously arise when, in a differentially rotating medium, the well-known inverse cascade of two-dimensional turbulence is halted by wave dispersion effects or by friction: jets represent a spatial organization of a turbulent flow. A present challenge is to fully understand the intermittent nature in time and space of these jets. I will review several approaches based on nonlinear concepts of Lagrangian chaos that have been recently developped. These approaches help to discriminate the regions of space which can act as horizontal barriers to mixing.
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