Jovian Winds from Voyager 2. Part I: Zonal Mean Circulation

Abstract

Independent measurements of Jovian cloud motions confirm previously published results on the general structure of Jupiter's zonal mean circulation. The new results are based on Voyager 2 images and measurement techniques which are different from those used in previous studies. The latitudes of the zonal jets agree with previous results, but there are some differences in the measured speed of the jets which exceed uncertainty estimates. These differences may be due to differences in sampling strategies. The structure of the zonal mean meridional velocity profile has still not been clearly resolved: mean meridional velocities generally differ from zero by no more than their estimated uncertainty. An analysis of successive measurements of the same cloud targets shows that most of the variance of individual velocity measurements is due to true variability of the winds. In agreement with the previous results the curvature of the zonal velocity profile is consistent with barotropic instability within most easterly jets, although the cloud morphologies visible in the images do not confirm that large-scale instabilities actually exist in these regions. Baroclinic effects may also be important in these regions. Large differences among independent estimates of eddy momentum transport indicate that this quantity has yet to be reliably determined.