climatology and meteorology


in meteorology, an elongated area of relatively high atmospheric pressure, almost always associated with and most clearly identified as an area of maximum anticyclonic curvature of wind flow.

relative humidity

the (dimensionless) ratio of the actual vapor pressure of the air to the saturation vapor pressure; usually expressed as a percent, and can be computed from psychrometric data.


radiosonde which is tracked by radar or radio-theodolite to measure the wind aloft.


instrument intended to be carried by a balloon up through the atmosphere, equipped with sensors to measure one or several meteorological variables (pressure, temperature, humidity, etc.), and provided with a radio transmitter for sending this information to the observing station.


(1) emission or transfer of energy in the form of electromagnetic waves (2) the process by which electromagnetic radiation is propagated through free space by virtue of joint undulatory variations in the electric and magnetic fields in space; this concept is to be distinguished from conduction and convection.


RAdio Detection And Ranging was an original active microwave sensor that became widely operational with the onset of World War II.


an accumulation of melt water on an ice surface, mainly due to melting snow, but in later stages also to the melting of ice; the initial stage consists of patches of slush.

psychrometric tables

tables prepared from psychrometric data and used to obtain vapor pressure, relative humidity, and dew point from wet- and dry-bulb temperatures.


an instrument used for measuring the water vapor content of the atmosphere; a type of hygrometer; it consists of two thermometers, one of which (the dry bulb) is an ordinary glass thermometer, while the other (wet bulb) has its bulb covered with a jacket of clean muslin which is saturated with distilled water prior to an observation; when the bulbs are suitably ventilated, they indicate the thermodynamic wet- and dry-bulb temperatures of the atmosphere; one variety is the assman psychrometer (a special form of aspiration psychrometer for which the ventilation is provided by a suction fan).

pressure tendency

the character and amount of atmospheric pressure change for a three-hour or other specified period ending at the time of observation.


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