A Linear Analysis on the Acceleration of Zonal Flow by Baroclinic Instability. Part II: Jovian Atmosphere

Abstract

The stability analysis of wave-zonal flow interaction which was developed in Part I is applied to the Jovian atmosphere. The analysis is made using a two-layer, quasi-geostrophic model on a midlatitude beta-plane. The physical data used as input to the model, e.g., the meridional temperature gradient, are provided by recent Pioneer and Voyager missions. Our results indicate that planetary waves generated by baroclinic instability near the Jovian cloud-top level may be responsible for the observed multiple zonal jets whose velocity changes sign with latitude. Our conclusion is obtained with the reservation that more accurate measurements are needed to fully understand the dynamics of Jupiter. In particular, the equator-to-pole and vertical temperature gradients are crucial for the present theory to be valid. The results support the findings of Williams who showed that multiple jet formation is possible on a beta-plane if the transition wavenumber k? (Rhines) takes on certain values based on the barotropic nature of the basic flow. However, it is shown in the present paper that the meridional wale of the alternating jets is closely tied to a functional relationship involving the baroclinic deformation scale and a turbulence closure approximation. It appears that one reason why multiple jets exist on Jupiter, as opposed to the single jet on the earth, is because the ?aspect ratio? between the characteristic deformation length and the planetary radius is very large compared to unity on Jupiter, while on the earth this ratio is close to unity. Therefore, our interpretation of the meridional scale of the alternating jets on Jupiter is based on the inherent dynamical scale in a baroclinic atmosphere, which was not explicitly considered in the previous barotropic theory by Rhines.