The basic motion of the giant planet interiors is almost certainly barotropic up to pressure levels where the visible and thermal-infrared optical depth of the atmosphere becomes small enough to allow both solar heating and thermal radiation to space. Hence, while horizontal temperature variations are observed on the giant planets at pressures less than about 1 bar, temperature variations are observed to decrease at higher pressures and presumably rapidly diminish to zero in the deep atmosphere. The dominating barotropic nature of the flow, combined with the large Coriolis forces on the giant planets, low viscosity, and the absence of significant surface friction, seems to result in a simple zonal circulation for all four giant planets. However, while molecular viscosity is low, turbulence in the atmosphere leads to considerable eddy viscosity. This, together with differential solar heating, leads to time-varying eddy motions (where by eddy motion we technically mean anything departing from the mean flow) including turbulence, large-scale vortices, and waves, which will now be discussed.
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