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Observing Cloud Height

Some tips for determining the height of clouds. You may also find a Dichotomous Key for Cloud Identification (developed by Dr. Tina Cartwright) helpful for this. An excellent web resource for background on observing clouds is http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/home.rxml

Low clouds

These are generally clouds made of water droplets whose base is below 2 km altitude (they can be made of ice when the temperature is cold enough, for example at high latitudes in the winter-time). Cloud types include stratocumulus, cumulus, stratus, cumulonimbus and nimbostratus. Fog can also be put in this class.

If you think these type of clouds are present there are some measurements you can make to estimate the altitude of the cloud base.

Mid-level clouds

For the CERES project, we define mid-level clouds as those whose base is between 2 and 6 km altitude. Cloud types are altostratus or altocumulus, and are generally but not always water clouds, depending on the atmosphere's temperature and other conditions at the cloud altitude.

High clouds

High clouds are those whose base is above 6 km. Types include cirrus, cirrocumulus and cirrostratus. These clouds can be either ice or water particles, but are more often ice. Water clouds tend to have definite edges, while ice clouds are more wispy. Persistent contrails (airplane tracks that don't just disappear as the airplane passes) are high clouds as well, and should be included as part of the observation. When you see contrails, please note their presence by checking the box on the report form.

Multiple cloud layers

There is often more than one cloud layer present, and if the lower layer is broken this can be observed from the ground. When this is the case, we would like to know what combination was present: low+mid, low+high, mid+high, or low+mid+high. It is understood that when solid cloud is present, a layer above it will not be observable from the ground.

Comment from the Field

Typically there are no points of reference in the sky's blue background to determine cloud height and we depend on identifying the cloud type to determine the altitude of the clouds observed.

This comment from the Cliffs of Dover, UK, on December 3, 2001, provides an example of a location with some unique points of reference in determining low level cloud altitudes fairly accurately.

"...Very gloomy day - lights needed on all day in the classroom. Cloud base no higher than about 600 feet above sea level. By the time of the second pass of the satellite at 1227UTC the cloud base was down to about 200 feet above sea level and visibility was down to about 2km. We are able to judge cloud base as we are about 300 feet above sea level, and can also see Dover Castle on the next hill, about a mile away. It is slightly higher than us and by it there are three tall radio masts - as they all gradually disappear from view we can judge the altitude of the cloud base!..."

Database icon View this and other reported cloud observations on the Observation database. Select Date - December 3, 2001 to view this observation along with the others made at various sites that day.





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