Martian Clouds
Although not as pronounced as on Earth, clouds are common features on Mars. The Martian atmosphere has only a trace of water vapor; however, the temperature and pressure is such that the atmosphere is usually close to saturation and produces clouds. Even from Earth based telescopes, clouds have been observed by transient brightening on the surface of Mars. Numerous cloud patterns have been seen from the Mariner and Viking spacecraft and have been classified into various categories (Carr, 1981; French et al. 1981):
Lee waves. These clouds form in the lee of large obstacles such as mountains, ridges, craters and volcanoes. The air in these regions undergoes wavelike oscillations.
Wave clouds. These clouds appear as rows of linear clouds. They are common at the edge of the polar caps.
Cloud streets. These clouds exhibit a double periodicity. They appear as linear rows of cumulus-like, bubble-shaped clouds.
Streaky clouds. These clouds have a direction without periodicity.
Fog or ground hazes. Fog usually occurs in low areas such as valleys, canyons and craters. It forms during the coolest times of the day such as dawn and dusk. Sometimes ground haze is caused by dust in the atmosphere; however, if the atmosphere is clear ground fog can be easily identified.
Plumes. These are elongated clouds. They appear to have a source of rising material and in many case are composed of dust particles.
Views of Martian Clouds
Cyclonic Disturbances
Along the edge of the polar cap, cyclonic disturbances are common during the late summer and fall. This storm system is located at the edge of the northern polar cap. In the foreground, frost can be seen as bright areas.
Lee Wave
This is a good example of a lee wave associated with an impact crater. Note the wave periodicity in the clouds.
Wave Clouds
Wave clouds usually occur at the lee of a large obstacle. They are often found at the edge of the polar cap, and in the Tharsis and Lunae Planum regions.
Cloud Streets
The cloud patterns illustrated by this image exhibits a double periodicity. These types of clouds usually occur close to the northern-polar cap and in the Tharsis and Syria Planum regions.
Streaky Clouds
Streaky clouds seem to be found most everywhere; however, they seem to be more concentrated in the highlands southwest of Syrtis Major.
Fog
Fog often appears in low-lying areas. It typically occurs in the southern hemisphere especially in the Argyre and Hellas basins. It forms frequently in craters. Occasionally, it occurs in higher regions such as Sinus Sabaeus and Solis Planum.
Clouds in Noctis Labyrinthis
This image shows early morning fog in the Noctis Labyrinthis, at the westernmost end of Valles Marineris. This fog, which is probably composed of water ice, is confined primarily to the low-lying troughs, but occasionally extends over the adjacent plateau. The region shown is about 300 kilometers across.
Dust Plume
This is an example of a dust plume in the Solis Planum region. This image was taken during the springtime for this region. Plumes are found primarily in the southern hemisphere, in highlands such as Syrtis Major and in elevated regions such as Tharsis.