HR: 11:50h
AN: GP42A-07    [Abstracts]
TI: Impossibility of Deep-seated Zonal Winds in Jupiter and Saturn
AU: * Liu, J
EM: ljj@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: Stevenson, D J
EM: djs@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 United States
AB: The zonal winds on the surface of the giant planets are very strong (100m/s) and stable (on a decadal time scale). Galileo probe observations suggest that the zonal flow on the giant planets might be deep seated, which supports the theory that these flows are the surface expressions of the flow on cylinders (Busse, 1976, Busse, 1983). This is based on the idea that there is a large non-electrically conducting region external to the metallic hydrogen region where the field is generated. In reality, shockwave experiments and theoretical calculations tell us that the electrical conductivity of hydrogen increases exponentially inward until it reaches the electrical conductivity of the metallic hydrogen. Therefore, if the zonal flow is the surface expression of the flow along the cylinders, it will interact with the poloidal magnetic field and produce a toroidal magnetic field, an associated poloidal electrical current and Ohmic dissipation. In steady state, this dissipation cannot be larger than the planetary net luminosity. This implies an upper bound for the penetration of zonal flows. We have performed two kinds of calculations to quantify this upper bound. We first assume that the observed surface zonal flow penetrates to the deep interior along the cylinders, but truncated to (near) zero at some spherical radius. We found that this radius corresponds to an electrical conductivity of about 0.001 S/m and is at 0.96 to 0.97 of Jupiter's radius and 0.88 to 0.89 of Saturn's radius. Second, we concentrate on a flow that is purely a function of cylindrical radius and establish a criterion for the maximum width of the jets that can penetrate to the deep interior. In both cases, we find that in the shell or cylinder where the flow declines to zero, the curl of the Lorentz force is not large enough to balance the shear of the zonal flow parallel to the rotation axis. Since there appears to be no other source of sufficient strength to provide this shear, we conclude that the assumed deep-seated flow is in fact impossible.
DE: 1595 Planetary magnetism: all frequencies and wavelengths
DE: 5704 Atmospheres (0343, 1060)
DE: 5734 Magnetic fields and magnetism
DE: 6220 Jupiter
DE: 6275 Saturn
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005