A basic equation in daytime visual range theory, relating the apparent luminance of a distant black object, the apparent luminance of the background sky above the horizon, and the extinction coefficient of the atmosphere, or the air layer near the ground. ...

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.

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

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

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

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

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

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.

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

Temperature based on an absolute scale.

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

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.

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% ...

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

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

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).

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

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