Cumulo- means "heap" or "pile" in Latin. Cumulus clouds are often described as "puffy", "cotton-like" or "fluffy" in appearance, and have flat bases. Cumulus clouds, being low-level clouds, are generally less than 1,000 m (3,300 ft) in altitude unless they are the more vertical cumulus congestus form. Cumulus clouds may appear by themselves, in lines, or in clusters.
Cumulus clouds form via atmospheric convection as air warmed by the surface begins to rise. As the air rises, the temperature drops, causing the relative humidity to rise. In this phase, water vapor condenses on various nuclei present in the air, forming the cumulus cloud. This creates the characteristic flat-bottomed puffy shape associated with cumulus clouds.
Cumulus clouds can form in lines stretching over 480 kilometres (300 mi) long called cloud streets. These cloud streets cover vast areas and may be broken or continuous. They form when wind shear causes horizontal circulation in the atmosphere, producing the long, tubular cloud streets. They generally form during high-pressure systems, such as after a cold front.
The height at which the cloud forms depends on the amount of moisture in the thermal that forms the cloud. Humid air will generally result in a lower cloud base. In temperate areas, the base of the cumulus clouds is usually below 550 metres (1,800 ft) above ground level, but it can range up to 2,400 metres (7,900 ft) in altitude. In arid and mountainous areas, the cloud base can be in excess of 6,100 metres (20,000 ft).
Some cumuliform clouds have been discovered on most other planets in the solar system. On Mars, the Viking Orbiter detected cirrocumulus and stratocumulus clouds forming via convection primarily near the polar icecaps. The Galileo space probe detected massive cumulonimbus clouds near the Great Red Spot on Jupiter.
Cumuliform clouds have also been detected on Saturn. In 2008, the Cassini spacecraft determined that cumulus clouds near Saturn's south pole were part of a cyclone over 4,000 kilometres (2,500 mi) in diameter. The Keck Observatory detected whitish cumulus clouds on Uranus. Like Uranus, Neptune has methane cumulus clouds. Venus, however, does not appear to have cumulus clouds.
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Cumulus cloud Facts for Kids. Kiddle Encyclopedia.