Zonal Jets and Eddies - Planetary Science and Satellite Oceanography at the Crossroads

The Team's Mission

Zonal jets play a prominent role in large-scale circulations of planetary atmospheres and oceans. Their presence has been established on all four solar system giant planets and in the terrestrial oceans and atmosphere. They are most familiar as the "sub-tropical jet stream" in the Earth's atmosphere and as a stable system of zonal (east-west) bands on the Jovian disk formed by the advected clouds. On Saturn, the jets appear as a system of "zones" and "belts." After their separation from the coast, powerful oceanic boundary currents such as the Gulf Stream and Kuroshio, as well as the Antarctic Circumpolar Current (ACC) may be held together by processes similar to those maintaining the jets on giant planets. The same processes may also be governing the recently discovered ubiquitous narrow oceanic jets detectable both on the surface and at great depth.

Recent decades were marked by advances in our understanding of the physics of zonal jets. This progress was largely stimulated (a) by the acquisition of new planetary data by the Galileo and Cassini spacecraft missions and the Hubble Space Telescope; (b) collection of new oceanic data using satellite altimetry and various instrumented floats; (c) new laboratory data obtained in advanced experimental facilities; (d) extensive high-resolution computer simulations of planetary and oceanic circulations, and (e) progress in our understanding of the interaction between anisotropic turbulence and waves.

One of the prevailing theories today attributes the generation and maintenance of the jets to the anisotropic inverse energy cascade, in which the anisotropization is due to the meridional variation of the Coriolis parameter, or beta-effect. In another theory, the deep-seated jets on gas planets result from flow two-dimensionalization due to strong background rotation and ensuing constraints imposed by the Taylor-Proudman theorem. Other theories are either linear or weakly nonlinear and employ various techniques from hydrodynamic stability theory.

This multi-pronged research has generated an abundant wealth of information but which is often disconnected between different disciplines. Further progress can be greatly facilitated by assessing, summarizing and diffusing this information between different areas of science. Such an effort is precisely the purpose of the proposed project which is being undertaken under the auspices of the International Space Science Institute. ISSI provides an ideal environment for international interdisciplinary collaboration necessary to carry out such an endeavor. To accomplish our goal, an International Study Team has been assembled. The original team is supported by the Associated Team which expands the coverage of the material and enhances the interdisciplinary nature of this effort. Our mission is to review, synthesize and summarize the current state of knowledge and understanding of the physics of zonal jets and their relationships with other processes in planetary systems. Over the duration of the project, we shall re-evaluate the state-of-the-art in various fields where the zonal jets play an important role, be actively engaged in cross-disciplinary information exchange, and prepare a multi-author publication on the physics of the zonal jets and their role in planetary circulations that will herald this effort.