Zonal Jets on the Giant Planets

Details Zonal Jets on the Giant Planets Zonal Jets on the Giant Planets

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p52a..04s&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #P52A-04

Physics

0343 Planetary Atmospheres (5210, 5405, 5704), 5210 Planetary Atmospheres, Clouds, And Hazes (0343), 5704 Atmospheres (0343, 1060), 5724 Interiors (8147), 5739 Meteorology (3346)

Scientific paper

The question of what causes the numerous east-west zonal jets on the giant planets has remained a mystery since high-resolution Pioneer and Voyager images were returned in the 1970s. A probable hypothesis is that small-scale turbulence undergoes an inverse energy cascade that reorganizes the energy into zonal jets, but whether this turbulence results from deep penetrative convection or shallow cloud-layer processes (e.g., thunderstorms) remains unknown. Here I provide a broad summary of this problem and proceed to describe several results on the effect of cloud-layer turbulence on the flow. I present 3D numerical simulations showing that cloud-layer thermal contrasts (resulting from sunlight or latent-heat variations in the upper troposphere) can drive numerous Jupiter-like zonal jets at the cloud level, in some cases including a superrotating equatorial jet resembling that on Jupiter. Furthermore, these simulations -- as well as linear, analytic calculations -- show that such shallow forcing can produce deep jets that extend far below the level of the forcing. This disproves the common assumption that jets produced by cloud-layer processes would be confined to these shallow layers. An implication is that, contrary to the claims of many publications, the winds measured by the Galileo probe to pressures of 22 bars might just as easily result from shallow forcing as from deep convective forcing. Detailed diagnostics show that the deep jets result from Coriolis accelerations acting on deep meridional circulations that are induced by the upper-level forcing. I also show that, under some conditions, vertical stretching of atmospheric columns can inhibit the standard jet-formation mechanism and lead to vortices instead of jets. Cloud-layer turbulence can also substantially modify pre-existing deep jets, leading to different jet patterns at the 1-bar cloud level than exist in the interior. On balance, these simulations support the idea that cloud-level forcing plays an important role in shaping the jet structure on giant planets, although this does not rule out an important role for deep forcing too. A future generation of coupled interior-atmosphere models will be required to fully assess the relative roles of deep and shallow forcing in driving jets on the giant planets.

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