The value of atmospheric pressure to which the scale of a pressure altimeter is set so as to indicate airport elevation. The altimeter setting is included as part of an aviation weather observation.

Anemometer which measures wind speed by the speed of rotation of 3 or 4 hemispherical or conical cups, each fixed to the end of a horizontal arm projecting from a vertical axis. See condenser-discharge anemometer, contact anemometer. Compare to bridled-cu ...

An optical instrument which consists of a sighting telescope mounted so that it is free to rotate around horizontal and vertical axes, with graduated scales so that the angles of rotation may be measured. Used to observe the motion of a pilot balloon.

A reversing thermometer (for seawater temperature) which is not protected against hydrostatic pressure. The mercury bulb is therefore squeezed, and the amount of mercury broken off on reversal is a function of both temperature and of hydrostatic pressure.

An instrument of the aspiration condenser type which measures the concentration and mobility of small ions.

The correction applied to an instrument to account for the effect of temperature upon its response characteristics.

The effect upon the measurement of rainfall caused by the presence of the rain gauge.

Reduction of visibility by strong winds blowing across dry ground with little or no vegetation. Visibilities of 1/8 mile or less over a widespread area are criteria for a Blowing Dust Advisory.

A system of physical units based on the use of the centimeter, gram. and the second as elementary quantities of length. mass. and time.

Physical equipment used in data processing. Compare to firmware, software.

Temperature of equilibrium between the liquid and vapor phases of a substance at a given pressure.

Instrument for measuring the intensity of radiant energy. Its principle is based on the variation of electrical resistance, with the incoming radiation, of one or both the metallic strips which the instrument comprises.

A thin metal disc partially evacuated of air used to measure atmospheric pressure by measuring its expansion and contraction.

A radar term for a single pulse of radio energy.

General term for an instrument which records the vertical electric current in the atmosphere.

Readily taking up and retaining moisture.

The greatest distance at which it is just possible to see and recognize with the unaided eye (1) in the daytime, a prominent dark object against the sky at the horizon, and (2) at night, a known, preferably unfocused, moderately intense light source.

An instrument used for the measurement of the reflecting, power (the albedo) of a surface. A pyranometer adapted for the measurement of radiation reflected from the earth's surface is sometimes employed as an albedometer.

An instrument developed by K. Angstrom for measuring the effective terrestrial radiation. It consists of four manganin strips, of which two are blackened and two are polished. The blackened strips are allowed to radiate to the atmosphere while the polishe ...

A Sunshine recorder of the type in which the time scale is supplied by the motion of the sun. The instrument, which is pointed at the celestial pole, consists of a hemispherical mirror mounted externally on the optical axis of a camera. The lens of the ca ...