While clouds appear in infinite shapes and sizes, they fall into
some basic forms. From his Essay of the Modifications of Clouds (1803),
Luke Howard divided types of clouds into several main categories: cirriform, cumuliform, stratiform, and nimbiform. Explore the four core cloud types and discover the science behind the names.
cirriform
The Latin word cirro means "curl
of hair." Composed of ice crystals, cirroform clouds are whitish and hairlike. They are the high, wispy clouds to first appear in advance of a low-pressure area such as a mid-latitude storm system or a tropical system such as a hurricane.
Cirriform clouds are high clouds existing between -25° and -85°C. As
a result, when near the horizon, their reflected light traverses a sufficient thickness of air to often cause them to take on a yellow or orange tint. With the sun on the horizon, this type of cloud is whitish. When the sun begins to sink below the horizon, they become yellow, then pinkish. When the sun is set, they are gray.
cumuliform
Generally detached clouds, cumuliform clouds look like fluffy white cotton balls. They show vertical motion, or thermal uplift, of air taking place in the atmosphere. They are usually dense in appearance with sharp outlines. The bases of cumulus clouds are generally flat, occuring at the same altitude where the moisture in rising air condenses. The principal characteristic of these clouds is vertical development in the form of rising mounds, domes, or towers. This is the contrasting form to the horizontally extended stratiform types.
stratiform
From the Latin word for "layer," these clouds are usually broad and fairly
wide spread appearing like a blanket. They result from non-convective
rising air and tend to occur along and to the north of warm fronts. The
edges of stratiform clouds are diffuse.
nimbiform
The special rainy cloud classification, which combines the three forms
cumulo, cirro, and stratus, is the nibiform category. These clouds are named after nimbus, the Latin word for rain. The vast majority of precipitation occurs from nimbiform clouds; these clouds
have the greatest vertical heights, as they hold a great amount of water.