In a system of moist air, the ratio of the mass of water vapor to the total volume of the system. Usually expressed as grams per cubic meter (g/m3).

An instrument whose calibration can be determined by means of simple physical measurements on the instrument. Compare to secondary instrument.

Temperature based on an absolute scale.

A temperature scale based on absolute zero. Same as Kelvin temperature scale.

A hypothetical temperature characterized by a complete absence of heat and defined as 0 K, -273.15 C, or -459.67 F.

The process in which incident radiation is retained by a substance. A further process always results from absorption.

A type of hygrometer which measures the water vapor content of the atmosphere by means of the absorption of vapor by a hygroscopic chemical.

Growth of a cloud or precipitation particle by the collision and union of a frozen particle with a super-cooled water drop.

The degree of conformity of an indicated value to an accepted standard value, or ideal value. See accuracy rating, measured accuracy.

A number of quantity defining a limit that errors will not exceed when a device is used under specified operating conditions. Accuracy rating can be expressed in a number of forms, i.e. in terms of the measured variable (+/- 1 C), percent of span (+/-0.5% ...

The volume of water required to cover one acre to a depth of one foot: 43,560 cubic feet.

An instrument which measures the intensity of radiation by determining the amount of chemical change( or fluorescence produced by that radiation.

The atmospheric pressure at the level of the barometer. May or may not be the same as station pressure.

The process by which one object becomes adhered to another by the binding action of ice.

A thermodynamic change of state in a system in which there is no transfer of heat or mass across the boundaries of the system. In an adiabatic process, compression always results in warming, expansion in cooling. Compare to diabatic process.

Pertaining to the action or effect of the wind. Derived from the name of the Greek god of the winds, Aeolus.

An anemometer utilizing the principle that the pitch of the aeolian tones generated by air moving past an obstacle is a function of the speed of the air. Largely a curiosity and has been put to no practical application in modem meteorology.

Of or pertaining to the air, atmosphere, or aviation. Also, same as antenna.

In general, any self-recording instrument carried aloft by any means to obtain meteorological data.

A self-recording instrument used on aircraft for the simultaneous recording of atmospheric pressure, temperature, and humidity.