9th September 2005
Cumulus Humilis
Source: Excerpt from The Book " Weather "
Distribution: Worldwide,
except Antarctica.Height: 2000 to 3500 feet. Cause: Weak convection. Associated Weather: None Cumulus clouds generally form as a result of localized pockets of warm air rising. The water vapor in the air condenses into well-defined, lumpy parcels of cloud at low level. The shape of these clouds gives rise to the name cumulus, which means heap in Latin.
Cumulus humilis is the smallest form of cumulus cloud and results from relatively weak convection (humilis means humble in Latin). This produces clouds that generally have flat bases and small, rounded tops. Technically, a cumulus cloud is considered to be a humilis formation if it is wider than it is tall, as estimated by an observer on the ground.
The level of the base of this small cloud is determined by the humidity of the surrounding air mass. In areas of high humidity, such as coastal and tropical regions, the base may start at around 2,000 feet but it may begin at much higher levels in dry areas. Often, cumulus humilis represents an early stage in the development of a cumulus cloud from stratocumulus to cumulus mediocris and then cumulus congestus. If conditions are right, some humilis clouds may eventually develop into cumulonimbus incus.
Because of its shallow depth, this cloud formation does not produce any significant weather. It can, however, give rise to turbulence during aircraft penetration of the cloud, but this effect is normally slight and short lived.
Cumulus humilis is widely distributed, occurring over all landmasses and oceans when conditions are right, except Antarctica, where the cold surface temperatures inhibit convection. Cumulus Humilis is also known as Fair Weather Cumulus.
Acknowledgement due: John W. Zillman, William J. Burroughs,
Bob Crowder, Ted Robertson, Eleanor Vallier-Talbot and Richard Whitaker.
Check out Skyscapes for cloud photos taken from the aircraft.
