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Observing Cloud Cover

An excellent web resource for background on observing clouds is http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/home.rxml

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A completely clear day might seem boring in a cloud observer project, but in fact this is one of the most important things a surface observer can report. Clear sky is easy to detect from the ground, because one observes against the uniform background of space. When looking down at the Earth, however, the background is highly variable and can make cloud detection very hard. One test to perform on clear days is to hold up your fist to block the sun, and look for a halo around it. DO NOT LOOK DIRECTLY AT THE SUN!!! A halo indicates the presence of very thin cirrus cloud.

Clear (>0 to 5%)

Partly Cloudy (5 to 50%)

Mostly Cloudy (50 to 95%)

Overcast (95 to 100%)

Choosing between these categories is easy at the extremes, but harder where they meet. You will have to estimate what fraction of the sky is covered by clouds. One good way to do this is to have everyone in the class make an estimate, and then average all the answers. This helps prevent bias which a single observer might introduce.

When multiple cloud layers are present, we would like this information for each cloud layer.

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