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A cloud base (or the base of the cloud) is the lowest altitude of the visible portion of a cloud. It is traditionally expressed either in metres or feet above mean sea level or above a planetary surface, or as the pressure level corresponding to this altitude in hectopascals (hPa, equivalent to the millibar ).
One type of map shows where VFR (visual flight rules) are in effect and where IFR (instrument flight rules) are in effect. Weather depiction plots show ceiling height (level where at least half the sky is covered with clouds) in hundreds of feet, present weather, and cloud cover. [27] Icing maps depict areas where icing can be a hazard for flying.
The laser is pointed upward, and the time required for reflected light to return to the station allows for the calculation of the height of the cloud base. Because of the limited coverage area (the laser can only detect clouds directly overhead), the system computer calculates a time-averaged cloud cover and ceiling , which is reported to ...
Cloud top pressure can also be used as an indicator of cloud top height. [1] The Cooperative Institute for Meteorological Satellite Studies (CIMSS) provides real-time cloud top pressure maps of the conterminous United States derived from data obtained from the GOES 11 and GOES 12 satellites. [2]
The cloud height, more commonly known as cloud thickness or depth, is the distance between the cloud base and the cloud top. [1] It is traditionally expressed either in metres or as a pressure difference in hectopascal (hPa, equivalent to millibar ).
The grouping of clouds into levels is commonly done for the purposes of cloud atlases, surface weather observations, [7] and weather maps. [40] The base-height range for each level varies depending on the latitudinal geographical zone. [7] Each altitude level comprises two or three genus-types differentiated mainly by physical form. [41] [5]
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Clouds height can vary depending on latitude; with cloud cover in polar latitudes being slightly lower and in tropical regions the cloud cover may extend up to 8,000m. The type of cloud is also a factor, with low cumulus clouds sitting at 300–1,500m while high cirrus clouds at 5,500-6,500m.