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S'COOL: Cloud Identification Tips

These tips are adapted from the workbook of the GLOBE Project.

Several things are useful to know in identifying and naming clouds according to the official classifications:
Clouds that are wispy and high in the sky are always cirrus of one type or another. If the cirrus clouds contain waves or puffs, then they are cirrocumulus. If they form continuous layers that seem to cover the sky high up, they are cirrostratus.

Clouds at middle altitudes are designated by the prefix "alto-". If in layers, they are altostratus; if in heaps and puffs, they are altocumulus.

Clouds that form at low altitudes (below 2,000 m) are either of the cumulus or stratus family. Clouds in the cumulus family are puffy and heaped. They sometimes look like cotton ball clouds; or you can see other shapes in them. Clouds in the stratus family form in layers or sheets that cover broad expanses of sky.

Low clouds that are dark, threatening and actually producing rain receive the designation "nimbus". Nimbostratus clouds cover the entire sky with broad sheets and produce steady rain. Nimbostratus clouds are larger horizontally than vertically. The rainfall associated with nimbostratus is typically of low to moderate intensity, but falls over a large area for an extended period of time.

Cumulonimbus clouds have dark bases and puffy tops, often anvil-shaped, and are sometimes called "thunderheads." In some cases, the top of the "anvil" may extend as a high cirrus cloud layer. They tend to produce heavy precipitation, typically accompanied by thunder and lightning. When such clouds are present, please make observations from a sheltered area!

Not Clouds! The Solar Aureole

A S'COOL participant in Oklahoma, Margaret Avard, shared these pictures. They capture a phenomenon that you may observe when the atmosphere is clear of clouds but contains some type of aerosol: dust, smoke, etc. If you observe this phenomenon during a S'COOL observation, you should report clear sky. But, we also invite you to include a report in the comments about the presence of the solar aureole and whether you can observe any visible haze layer along the horizon.

Looking at the sky away from the Sun it looks completely clear and blue
Carefully looking at the sky near the Sun reveals a bright region around it. This is called the solar aureole. It is a brighter area right around the Sun which is caused by forward scattering from the aerosols. This means that sunlight hits the aerosol particles and is deflected just a little bit, spreading the brightness of the Sun over a wider area.
Looking toward the horizon you can see a faint haze layer indicating the presence of aerosols in the air
A better view of the haze layer along the horizon, including the resulting scattering of rays from the Sun visible at the top of the image. The aureole is nearly always present. It is smaller in cleaner air and broader when more aerosol (dust, smoke, etc) is present. Because of the brightness of the Sun, and the fact you should never look directly at the Sun, most people won't notice it unless it's quite pronounced.