climatology and meteorology


an instrument which measures the water vapor content in the atmosphere; there are several different means of transduction used in measuring this quantity and hence various types of hygrometers; these are: a) the psychrometer, which utilizes the thermodynamic method; b) the class of instruments which depends upon a change of physical dimension due to absorption of moisture (hair hygrometer, for example); c) those which depend upon condensation of moisture (dew point hygrometer); d) the class of instruments which depend upon the change of chemical or electrical properties due to absorption of moisture, and some others.


any product of condensation or sublimation of atmospheric vapor, whether formed in free atmosphere or at the earth's surface; also any water particles blown by the wind from the earth's surface.


(1) water vapor content of the air. (2) some measure of the water-content of air; see also absolute humidity, relative humidity, specific humidity, dew point.


a deposit of interlocking ice crystals (hoar crystals) formed by direct sublimation on objects, usually those of small diameter freely exposed to the air, such as tree branches, plant stems and leaf edges, wires, poles, etc.; the surfaces of these objects are sufficiently cooled, mostly by nocturnal radiation, to cause the direct sublimation of the water vapor contained in the ambient air.

high-level clouds

typically thin, white clouds above 6,000 meters (20,000 feet); at these altitudes, temperatures are so cold that clouds are composed primarily of ice crystals; includes cirrus, cirrocumulus and cirrostratus clouds.


area of high pressure in the atmosphere; used interchangeably with anticyclone.

heat source

process, or region, in which energy is added to the atmosphere in the form of heat.

heat sink

process, or region, in which energy is removed from the atmosphere in the form of heat.

heat flux

the amount of heat transferred across a surface of unit area in a unit time.

heat budget

relation between fluxes of heat into and out of a given region or body and the heat stored by the system; in general, this budget includes advective, evaporative, and other terms as well as a radiation term.


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