There are three regions in Saturn's atmosphere, as shown in this picture, where clouds of a particular kind, or clouddecks, are to be found. There is a clouddeck of ammonia clouds, a clouddeck of ammonia hydrosulfide clouds, and a clouddeck of water clouds (H2O).
The location of the clouds is predicted based upon the temperature at which vapor will condense into droplets. The temperature at which the condensation occurs, according to the temperature profile shown in the figure by the black line, is where the clouds ought to be.
The diagram shows that the temperature in the troposphere goes from about -300 degrees (100 K) to about +80 degrees (300 K).
The first clouddeck, made of ammonia clouds is found at about 100 km below the tropopause, where the temperature becomes about 150 K. The second clouddeck, made of ammonium hydrosulfide clouds is found at about 170 km below the tropopause, where the temperature becomes about 200 K. And the third clouddeck, made of water clouds is found at about 130 km below the tropopause, where the temperature becomes about 270 K (freezing temperature for water).
Can you imagine that, temperatures bellow the third cloud level can actually reach tropical levels.
This mosaic shows the entire planet, including features like Saturn's ring shadows and the terminator, the boundary between day and night.
The data were obtained in February 2006 at a distance of 1.6 million kilometers (1 million miles) from directly over the plane of Saturn's rings, which appear here as a thin, blue line over the equator. The image was constructed from images taken at wavelengths of 1.07 microns shown in blue, 2.71 microns shown in green, and 5.02 microns shown in red.
The blue-green color (lower right) is sunlight scattered off clouds high in Saturn's atmosphere and the red color (upper left) is the glow of thermal radiation from Saturn's warm interior, easily seen on Saturn's night side (top left), within the shadow of the rings, and with somewhat less contrast on Saturn's day side (bottom right). The darker areas within Saturn show the strongest thermal radiation. The bright red color indicates areas where Saturn's atmosphere is relatively clear. The great variety of cloud shapes and sizes reveals a surprisingly active planet below the overlying sun-scattering haze.
The brighter glow of the northern hemisphere versus the southern indicates that the clouds and hazes there are noticeably thinner than those in the south. Scientists speculate that this is a seasonal effect, and if so, it will change as the northern hemisphere enters springtime during the next few years.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The Visual and Infrared Mapping Spectrometer team is based at the University of Arizona where this image was produced.
For more information about the Cassini-Huygens mission http://saturn.jpl.nasa.gov . The visual and infrared mapping spectrometer team homepage is at http://wwwvims.lpl.arizona.edu .
Image credit: NASA/JPL/University of Arizona