The energy spectra of the zonal flows on Jupiter and Saturn obey the scaling law EZ (n) = CZ (Ω /R)2 n-5 in the range of total wave numbers n not affected by large scale friction (Ω and R are the rotation rate and the radius of the planet, and CZ is an order-one constant). These spectra broadly resemble their counterpart obtained in our recent simulations [Huang et al., Phys. Fluids, 13, 225-240 (2001)] that represents a strongly anisotropic flow regime evoked by the planetary vorticity gradient. It is conjectured that this regime governs the large scale circulations and the multiple zonal jets on giant planets. More recent simulations with linear drag also exhibit the same behavior. Preliminary comparisons with the scarce data available for the other two giant planets are consistent with the above scaling. The combined effect of the energy condensation in the lowest zonal modes and the large scale friction on generation and maintenance of strong equatorial jets will be discussed.
|Published - 1 Nov 2001