cumuliform adj : shaped like a cumulus cloud

''' Cumulus clouds usually have a puffy cotton-like appearance, with noticeable vertical development and clearly defined edges. They can be found alone, in lines, or in clusters. Factors like instability, moisture, and temperature gradient, make cumulus clouds precursors of many other types of clouds, e.g cumulonimbus clouds. In some cases these clouds can be associated with dust devils, landspouts, waterspouts and tornadoes. Cumulus means heap or a pile in Latin.

Formation

Cumulus clouds are formed when air rises and reaches a level where the moisture in the air condenses. This is usually through convection where a parcel of air is warmer than the surrounding air. As it rises, the air cools at the dry adiabatic lapse rate (approximately 3°C per 1000ft or 1°C per 100m), while the dewpoint of the air falls by 0.5°C per 1000ft. When the temperature of the air reaches the dewpoint, water condenses out of the air to form a cloud. The size of the cloud depends on the temperature profile of the atmosphere and the presence of any inversion. If the top of the cumulus cloud is above the freezing level, then precipitation from the cloud is possible.

In windy conditions, the clouds can form lines (Cloud streets) parallel with the wind. In mountainous areas, they can also form lines across the wind due to the presence of lee waves above the clouds.

Over the sea, cumulus clouds may be found in regularly spaced lines. The best examples of these lines are found in the trade winds where they extend for many miles. These lines create a pattern in the vertical movement of air, causing it to roll horizontally. Between the lines of cloud are stronger, more gusty, and slightly veering winds; but beneath the lines of cloud, somewhat lighter and more backing winds prevail.

The height at which the cloud starts to form (cloud base), depends on the amount of moisture in the air parcel that forms the cloud. In temperate areas, the base of the cumulus clouds is usually up to 8,000ft (2,400m). In arid and mountainous areas, the cloudbase can be in excess of 20,000ft (6,000m).

Glider pilots often use cumulus clouds as a good indicator of the rising air or thermal underneath.It is one of the four clouds (The Cumulus, stratus, cirrus, and cumulonimbus clouds)

See also

• Clouds
• List of cloud types

External links

• Cumulus cloud at BBC Weather
• Cumulus cloud page at University of Richmond internal site