CONVECTIVE CLOUDS OF GREAT VERTICAL EXTENT
These types of clouds are most often detached clouds, generally
dense and with sharp outlines, developing vertically in the form of rising
mounds, domes or towers, having their bases located in the low level etage.
The sunlit parts of these clouds are mostly brilliant white. Their base is
relatively dark and nearly horizontal. Since these clouds may grow from regions
above freezing to levels well below freezing, they may be composed
solely of water droplets, supercooled water droplets, ice crystals, snowflakes,
ice pellets or a combination of all. These clouds form in an unstable
environment which allows air parcels to continue to rise once started either
through forced lifting or heating and are sometimes referred to as "clouds
of ascending air currents.".
take on a variety of shapes. This image, of
cumulus humilis, (of small size) is characterized by only a small
vertical extent and may appear flattened. It never produces precipitation. They
are sometimes called fair-weather cumulus. Cumulus mediocris clouds are of moderate vertical extent, with small protuberances and sproutings
at their tops. They generally give no precipitation.
The tops of these towers occasionally are formed of
small "puffs" which may detach themselves successively from the main
body of the cloud. They are then carried away by the wind and
disintegrate more or less rapidly, occasionally producing virga.
Cumulus congestus often develops into cumulonimbus type clouds.
cloud has grown to resemble a cauliflower with strong sproutings and generally
sharp outlines and often great vertical extent, a cumulus congestus cloud
has developed. Cumulus congestus often release abundant precipitation in
the form of showers. If a cumulus congestus cloud resembles a narrow, very
high tower, it often is called a towering cumulus, although a more proper
designation would be cumulus castellanus.
Cumulonimbus clouds, with the anvil tops as seen in the distance in this
image, are heavy and dense clouds with considerable vertical extent, in the
form of a mountain or huge towers. The clouds to the front are cumulus and
towering cumulus. At least part of its upper portion is usually smooth, or
fibrous or striated, and nearly always flattened; this part often spreads out
in the shape of an anvil or vast plume as shown. The top may reach to the
tropopause. Under the base of this cloud, which is often very dark, there are frequently low ragged clouds either merged with it or not, and precipitaion of the showery form, often very intense.
When cumulonimbus covers a large expanse of the sky, it can easily
be confused with nimbostratus, especially when identification is based solely
on the appearance of the undersurface. In this case, the character of the
precipitation may help to distinguish cumulonimbus, which produces a showery
type and is often accompanied by lightning and thunder, from nimbostratus,
which produces a steady, continuous precipitation.
Certain cumulonimbus clouds appear
identical to cumulus congestus. The cloud should be called cumulonimbus
as soon as at least a part of its upper portion loses the sharpness of
its outlines or presents a fibrous or striated texture. If it is
accompanied by lightning, thunder or hail, it is a cumulonimbus.
Cumulonimbus is composed of water droplets, supercooled droplets and ice
crystals, snowflakes, snow pellets, ice pellets or hail stones.
Cumulonimbus may be described as a "cloud factory," and it may produce
more or less thick patches or sheets of cirrus spissatus, altocumulus,
altostratus or stratocumulus by the spreading out of its upper portions
and by the dissipation of its subjacent parts. The spreading of the
highest part usually leads to the formation of an anvil.
Copyright © 1996-2007 Texas A&M
University, Texas A&M Meteorology
Department and Marion Alcorn.