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Name: Stacy M.
Status: student
Age: 14
Location: N/A
Country: N/A
Date: 6/4/2003


Question:
Does pressure effect the cloud type?


Replies:
Stacy, Pressure is not the most important factor in which cloud type might be present, although certain cloud types are more common in high pressure systems than in low pressure systems.

The height at which the cloud occurs and, along with that, the temperature of the air, as well as the relative humidity, type of vertical motion in the atmosphere, and the type of nuclei that the precipitation might form, on are all factors. For example, stratus clouds are formed by the general lifting of a layer of air, whereas cumuloform clouds are formed by air lifted in much smaller convective cells of air that rise above warm areas of the Earth's surface. Cirrus (ice) clouds form at the greatest heights, where the air is very cold and can thus produce ice particles.

I could go on for quite some time as to how these factors affect cloud type, as all of these factors in combination can form various cloud types.

David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory


Dear Stacey-

Air pressure and cloud type are independent of each other. Low, middle, and high clouds can occur with low surface air pressure as well as high surface air pressure. In general, more clouds of various types occur with low pressure. High pressure is usually associated with fair weather. But low clouds are common with high pressure also.

Clouds form when the air becomes saturated, usually due to a gradual "lifting" of the moist layer of air. When the air descends, the clouds evaporate, and skies are fair.

Wendell Bechtold, meteorologist Weather Forecast Office, St. Louis, MO


For starters, remember that the higher the altitude, the lower the atmospheric pressure will be.

Clouds are classified on the basis of their form and height. Three basic forms are recognized:

1) Cirrus-clouds are high, white and thin. Form @ 6000 m. They can also occur as patches composed of small cells or as delicate veil-like sheets or extended wispy fibers that often have a feathery appearance.

2) Cumulus-middle clouds @ 4000 m. Clouds consist of globular individual cloud masses. Normally they exhibit a flat base and have the appearance of rising domes or towers. Such clouds are sometimes described as having a cauliflower structure.

3) Stratus-low clouds @ 2000 m. Clouds are best described as sheets or layers that cover much or all of the sky. While there may be minor breaks, there are no distinct individual cloud types.

Robert Trach


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