Colours and motions in the atmosphere of Jupiter.

Pole-to-pole microdensitometer scans of Jupiter images, taken at red, green, blue and UV wavelengths, for the 1970, 1972, 1973 and 1974 apparitions have been used to study the colours on Jupiter. Variations with latitude of the colour ratios B/R and UV/R have been attributed to variations in the intensity of the 'reflected' radiation at blue and UV wavelengths. The colour ratio G/R appears to be approximately constant with latitude. The variations in B/R and UV/R correspond to the visual appearance of Jupiter; high values of B/R and UV/R coincide with zonal regions and low values occur in belted regions. The use of a simple scattering model and a simplified solution to radiative transfer theory have shown that Jupiter's atmosphere in the zonal regions can be approximated by a scattering atmosphere above a reflecting layer. The scattering atmosphere must consist predominantly of molecules, but with some admixture of aerosols. To explain the colour of the belted regions it is necessary to invoke the existence of chromophores (i.e. particles that absorb preferentially at blue and UV wavelengths). From 1972 to 1974 there seems to be a systematic colour difference between the northern and southern zones. This appears to be due to changes in the albedos of these regions with time. These changes are attributed to changes in cloud properties. The scattering model indicates that Jupiter's aerosol layer may vary in density, thickness and type of aerosol with time, on a global scale. There is an almost linear decrease in the colour ratios G/R, B/R and UV/R towards the centre of the Great Red Spot. This suggests that the top of the Great Red Spot consists of chromophores in the form of an anvil-shaped cloud, similar to some storm systems on Earth. There is a strong correlation between high 5? emission and low values of B/R, and vice versa. There appears to be no such correlation at 7.5?, 8-14? and 20?. The lifetimes of dark spots and red spots appear to be greater than those of light spots by a factor of five or more. Observations suggest that dark spots and red spots can undergo longitudinal oscillations, but light spots cannot. All spots remain at a constant latitude throughout their lifetime.