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''This article refers to meteorology. For the airborne base of the TV series Captain Scarlet and the Mysterons, see Cloudbase.'' The cloud base (or the base of the cloud) is the lowest altitude of the visible portion of the cloud. It is traditionally expressed either in m or feet above mean sea level (or planetary surface), or as the corresponding pressure level in hectopascal (hPa, equivalent to millibar). ==Measurement== The height of the cloud base can be measured using a ceilometer. This device reflects a beam of light off the cloud base and then calculates its distance using either triangulation or travel time. Alternatively, the cloud base can be estimated from surface measurements of air temperature and humidity by calculating the lifted condensation level. One method for doing this is as follows: #Find the difference between the surface temperature and the dew point. This value is known as the "spread". #Divide the spread by 4.4 (if temperatures are in °F) or 2.5 (if temperatures are in °C), then multiply by 1000. This will give you cloud base in feet AGL (Above Ground Level). A shortcut to the above method when temperatures is measured in °C is to simply multiply the spread by 400. #Add the results from step (2) to the Field Elevation (ft) to get cloud base ASL (Above Sea Level) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「cloud base」の詳細全文を読む スポンサード リンク
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