This image of Martian clouds illustrates the fact that they are found only in the equatorial region.
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Image from: Hubble
Unlike the Earth, where clouds are found around the entire globe, on Mars, clouds seem to be plentiful only in the middle latitudes, as shown in this Hubble telescope image. This may be because water of Mars may only be found at mid-latitudes. Many of the cloud formations also seem to be due to topographic forcing by Olympus Mons.
As early as 1796 scientists were reporting "yellow", and "white" or "bluish" clouds in the Martian atmosphere. However, it wasn't until the Mariner 9 mission that clouds of water were positively identified. Mars Global Surveyor is providing more proof of the existence of water clouds.
More study is needed to understand just how the clouds come and go in the Martian atmosphere. For example, even though clouds have been found, there is still little evidence when and where it actually rains on Mars, if at all. Atmospheric temperatures reported by Mars Pathfinder during its decent indicate that it may be too cold in the cloud forming region of the Martian atmosphere for droplets to fall to the ground as liquid, but it may be cold enough for the condensation of CO2 droplets.
As a first step in answering some of those questions, Mars Pathfinder took measurements of many clouds in the Martian sky from the surface of Mars itself. Scientists are studying images of the Martian sky from the 80-day mission to get their first assessment of Martian weather patterns. The Mars '98 mission will carry a weather sounder, much like a terrestrial weather satellite. Then scientists expect to receive much more comprehensive data about Martian weather.
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