How Clouds Work
by Jessika Toothman
Types of Clouds
Cirrus clouds hover high above a solitary oak tree on a ridge in the U.K.
Travelpix Ltd/Photographer's Choice/Getty Images
Whether they look like layers of white frosting or wisps of cotton candy, clouds with similar shapes can form in many regions of the atmosphere. Here's a run-down:
High-level clouds
High-level clouds are typically prefixed by "cirro" and may include cirrus, cirrocumulus and cirrostratus clouds. The latter may cover the sky with a milky blanket, still allowing some weak sunlight and moonlight to filter through. Cirrostratus clouds may be such a thin layer that they're only detectable by the halo they cast around the sun or moon. Cirrocumulus clouds usually create patterns of patchy cotton balls high in the sky. They may also form in bands, creating a wavy appearance. Cirrus clouds appear as white, delicate, wispy stripes or fans that often curve with the wind, which can be useful in determining air patterns. The bottoms of high-level clouds generally begin at altitudes between 6 to 12 kilometers (20,000 - 40,000 feet) above Earth's surface [source: Levine].
Mid-level clouds
Mid-level clouds are usually prefixed by "alto" and include altocumulus and altostratus clouds. Altocumulus clouds either appear as sheets of little round clouds or as parallel stripes of clouds. Though similar to cirrocumulus clouds, altocumulus clouds form at lower altitudes and feature shading on their textured surfaces. Altostratus clouds usually consist of a solid, thick layer of clouds that don't let in enough sunlight to penetrate to the ground to let shadows form. The bottoms of mid-level clouds usually begin around 2 to 6 kilometers (6,500 - 20,000 feet) above the ground [source: Levine].
Low-level clouds
The bottoms of low-level clouds typically reside below altitudes of two kilometers (6,500 feet) and may include cumulus, stratocumulus and stratus clouds [source: ­Tarbuck]. Stratus clouds give the sky an overcast appearance and can resemble fog. Fair-weather cumulus clouds are the large fluffy, clouds often seen on bright blue days, with distinct edges that resemble different shapes. Stratocumulus clouds are low and lumpy, usually with frequent gaps where sunlight or moonlight shines through. These clouds can be diffused over wider distances, resembling regular cumulus cloud with less-defined edges.
Cumulonimbus clouds, like these above French Polynesian waters, may mean rain is on the way.
Jeff Foott/Discovery Channel Images/Getty Images
Vertically-developed clouds
Also called multi-layer clouds, this category can include nimbostratus clouds (dark and low-hanging) and cumulonimbus clouds (large and associated with thunderstorms). Some people consider nimbostratus clouds low-level clouds, but because their height can creep well into in the mid-level range, we've included them in this category.
So now that we have an understanding about the different types of clouds in the skies above us, just how exactly do they get there? Go to the next page to read about where clouds come from. ­
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