Six major types of clouds form in Mars's atmosphere. The polar hood is a haze of water and perhaps carbon dioxide ice that forms over the polar regions in the fall and can cover much of the northern plains. Wave clouds form on the sheltered side of large obstacles, such as craters, and have very distinct ridges. Convective clouds form in high areas at midday. Orographic clouds form when air lifts over large-scale objects like Olympus Mons, and are most common in spring and summer when the water vapor content of the air is highest.
Ground hazes occur in low areas at dawn and dusk and probably consist of water ice.
Wispy high-altitude clouds sometimes occur just at dawn and dusk. The Viking 2 lander recorded images of water-ice frost during the winter. Image Gallery Return to Cosmiverse Reference Library Microsoft Corporation. All Rights Reserved. Cosmic Voyage 2000.