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BY GEORGE: Clouds and Cloud Formation
Submitted by George Elliott on Thu, 01/12/2012 - 3:31pm.
One of the most beautiful aspects of the atmosphere in which we live are clouds. Clouds come in many forms, and each type has its own characteristics and formations. Most of us generally take cloud types for granted, unless a storm approaches or we’re riding down an open highway on a warm summer afternoon, trying to make pictures out of the billowing white, fluffy clouds hanging low above our heads. In any case, I thought it interesting to take a little closer look at the beauty just above.
The basic clouds are identified on the basis of their form and approximate height above the ground where they normally occur. The names of the basic clouds are composed of the following roots: “cirrus,” meaning feathery or fibrous; “stratus,” as in stratified or layered; “cumulus,” as in heaped up; and “nimbus,” meaning the rain clouds.
High clouds, forming at 23,000 feet or higher, are entirely made of ice crystals. These include: Cirrus, the wispy feathery clouds, sometimes called “Mare’s Tails” for their appearance; Cirrostratus, a more layered thin sheet of ice clouds; and Cirrocumulus, more of a rounded type high ice cloud.
Middle-layer clouds, generally forming between 6,500 and 23,000 feet above the earth are made up of water droplets, and may contain some ice crystals. These clouds include: Altostratus (middle-layer stratified clouds) and Altocumulus (middle-layer fluffy type clouds).
The low clouds, forming below 6,500 feet, include Stratus, Stratocumulus, and Nimbostratus (the rain or snow cloud). These clouds are made up of water droplets.
Lastly, there are clouds of vertical development. These include clouds with bases below 6,500 feet, but may extend upwards to over 60,000 feet. The tallest towering clouds are Cumulonimbus clouds. These are the thunderstorm clouds, made up of water droplets, and high enough up into the atmosphere, ice crystals. The billowing, fluffy, white clouds, called Cumulus, also fall into this category, but do not extend as high into the atmosphere as do Cumulonimbus clouds. Cumulus clouds can be small cotton-like puffs, or towering Cumulus, referred to as Cumulus Congestus.
There are other adjectives applied to the basic names to further describe particular cloud types, but for general purposes here, it is enough to know the basic varieties.
In order for clouds to form, the air must cool, and there must be enough water vapor in the air to condense into water droplets or ice crystals. Additionally, and fundamentally, there must be some type of nuclei, i.e., (hygroscopic nucleus). A hygroscopic nucleus is an extremely small free-floating particle in the air. Examples of floating particles include dust, soot, salt crystals, and even some extremely small solid particles.
Air cools in three basic ways: The air itself comes in contact with a cold surface, the air rises (rising air expands and cools), and/or rain or snow falls and evaporates into the air, thus cooling the surrounding environment. Any one or combination of these things can be occurring simultaneously. Winds can obviously blow over colder surfaces, winds can be driven up the sides of mountains, rising and thusly expanding and cooling, fronts and pressure systems can cause the air to rise, and of course, rain and snow evaporate upon falling through the atmosphere.
The physics of the atmosphere and cloud formation is quite a complicated science, but it sure yields beautiful examples of nature at work.
By: George Elliott