9th September 2005
Stratocumulus
Source: Excerpt from The Book " Weather "
Distribution: Worldwide. Height: 2000 to 6500 feet. Cause: Lifting of a large air mass, followed by condensation combined with relatively weak instability at cloud level. Associated Weather:
Normally none, but may produce light precipitation if cloud is sufficiently thick.0ne of the most common clouds worldwide, stratocumulus is a good indicator of moisture in the lower levels of the atmosphere. It usually occurs between 2,000 and 6,500 feet. Stratocumulus usually has a ragged appearance along its upper surface, but can have a well-defined and flattish base. It tends to form in comparatively shallow layers, sometimes several hundred miles wide. The color of the cloud may vary from white to dark gray, depending on the light conditions and the thickness of the deck. Its somewhat lumpy appearance, indicative of convection within the cloud, is what distinguishes stratocumulus from stratus.
Two processes may give rise to strato-cumulus, either separately or in combination. In the first, a large, moist air mass is lifted by a frontal system or a landmass to a level where condensation occurs; slight instability at cloud level then creates the cloud's cumuliform shape.
The second process involves pockets of warm air rising from the ground as a result of weak convection, giving rise to condensation at the same level over a wide area.
In this case, the clouds may subsequently develop into cumulus humilis, and some of these may even develop into cumulonimbus clouds.
Normally, if stratocumulus has not developed vertically by mid-afternoon, the time of maximum ground temperature, it will tend to dissipate, resulting in a clear evening sky. If it is sufficiently thick, stratocumulus may produce light drizzle, or snow in sub-zero temperatures, but this is not common.
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.
