Jovian Clouds and Haze

At wavelengths from the near-ultraviolet (0.2 μm) to the infrared (5 μm) Jupiter’s appearance is dominated by contrasts produced by clouds and haze. It is important to understand the distribution and optical and physical properties of cloud and haze particles because they play a major role in the radiative heat budget, and they can tell us about atmospheric processes such as stratospheric circulation and tropospheric meteorology. The study of jovian clouds and haze also provides insight needed for interpretation of spectra of extra-solar giant planets. This chapter is concerned with the chemical and physical properties of cloud and haze particles, their vertical and horizontal distributions, their radiative properties, and their microphysical properties. These topics are entwined with the chemistry and composition of the troposphere and stratosphere, atmospheric dynamics and auroral processes that are the principal subjects of chapters in this volume by Taylor et al., Moses et al., Ingersoll et al., and Yelle et al. This chapter is divided into two main sections focusing on clouds and haze in the troposphere and stratosphere. The term “haze” will be used for a very dispersed and nearly uniform, ubiquitous layer of sub-micron particles in the upper troposphere (200 – 500 mbar) and for particles in the stratosphere (pressure less than 100 mbar). We use the term “clouds” for the more variable clouds of larger particles at deeper levels. These are further subdivided into the categories of chemical composition, physical properties, distribution, and microphysics. Both observations and theoretical treatments of each of these are given, but with emphasis on the observations since it is in that domain that most of the information resides. There is a large body of observational evidence relevant to studies of jovian clouds, with contributions from ground-based and earth-orbital telescopes over a long period of time, and major concentrated bursts from the Pioneer, Voyager, Galileo and Cassini spacecraft. In this chapter we give emphasis to research activity after 1986. The reader is encouraged to consult West et al. (1986) for a review of theory and observational results from Pioneer, Voyager and ground-based studies prior to 1986.