Zonal motion and structure in Jupiter's upper troposphere from voyager infrared and imaging observations

Abstract

Voyager infrared data are used to produce global cylindrical projection digital maps of temperature at the 270- and 150-mb pressure levels, infrared cloud optical depths at 45- and 5-μm wavelength, and the ammonia abundance near the 680-mb level. Voyager imaging data are used to produce maps of orange reflectivity and violet reflectivity (effective wavelengths of 0.58 and 0.41 μm, respectively). The zonal motions of the dominant structures in each of the quantities are evaluated using cross-correlation of the maps. Structures in the maps of cloud optical depths, ammonia abundance, and visible reflectivities show the same zonal motion at almost all latitudes. The dominant upper tropospheric thermal structures move at a rate which is far different than the cloud indicators, and they remain stationary with respect to the bulk rotation of the planet. Comparison of these motions with the zonally averaged thermal wind shear inthe upper troposphere indicates that the thermal structures move at a rate far different than the local fluid velocity. We present a simple theory which suggests that these slowly moving thermal structures could represent the influence of a disturbance seated in a slowly moving region deep in Jupiter's atmospheres, although this explanation is not unique. Intercomparison of the motions and longitudinal alignment of the various cloud indicators with the thermal wind shear in the upper troposphere shows that the few latitudes at which differences exist correlate strikingly with latitudes of largest shear, suggesting that the observed differences may reflect height differences in observed cloud features. Fourier analysis of the maps of temperature at 270-mb show a robust stationary feature at a zonal wavenumber of 9 near 15° N latitude. The maps of cloud optical depth at 45 μm show a feature at zonal wavenumber 11 near 20° N. These periodicities may be related to similar structures recently detected in groundbased observations, and their longevity and robustness may indicate preferred wavemodes of the atmosphere.