Modeling Deep Convection-Driven Zonal Flows on the Giant Planets

Details Modeling Deep Convection-Driven Zonal Flows on the Giant Planets Modeling Deep Convection-Driven Zonal Flows on the Giant Planets

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.1136a&link_type=abstract

American Astronomical Society, DPS meeting #38, #11.36; Bulletin of the American Astronomical Society, Vol. 38, p.1294

Astronomy and Astrophysics

Astronomy

Scientific paper

The large-scale zonal winds observed on the Giant Planets strongly differ. On Jupiter and Saturn, strong prograde equatorial jets are flanked at higher latitudes by alternating, smaller length-scale bands. In contrast, Uranus and Neptune's surface zonal winds are dominated by retrograde flow in the equatorial region, flanked by one large prograde jet in each hemisphere. Here we will demonstrate that deep convection in a rotating spherical shell can generate zonal flows like those observed on all four of the Giants Planets. Numerical simulations of Boussinesq rotating convection can generate either prograde or retrograde equatorial jet flows, and their direction depends on the relative strength of buoyancy and Coriolis forces in the system. The non-dimensional ratio of these two forces is called the modified Rayleigh number, Ra*. In our deep convection simulations the value of Ra* controls the dynamics and the flow direction of the equatorial jet. At Ra* << 1, angular momentum transfer by cylindrical Reynolds stresses acts to generate prograde equatorial jets, similar to those observed on Jupiter and Saturn. In addition, smaller wavelength Rhines scale jets form at high latitudes. This produces a clear discontinuity in the latitudinal jet scales across the spherical shell tangent cylinder. As Ra* approaches unity, the cylindrical symmetry of the flow weakens and the equatorial jet reverses direction, becoming retrograde, while the high latitude zonal flow in each hemisphere takes the form of a single, strong prograde jet. Thus, our low Ra* rotation-dominated models produce surface zonal flows similar to those observed on Jupiter and Saturn, whereas our high Ra* buoyancy-dominated models produce surface zonal flows that are similar to those observed of Uranus and Neptune.

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