The source of illumination for an antenna reflector. Also called antenna feed.

The measurement and computation of wind speeds and directions at various levels above the surface of the earth. Methods include pilot balloon observations, rabals, rawin or rawinsonde observations, radar tracking, or acoustic sounding.

A type of electrical thermometer consisting of two thermocouples which are series-connected with a potentiometer and a constant-temperature bath. One couple, called the reference junction, is placed in a constant-temperature bath, while the other is used ...

See evaporative opportunity.

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.

The process whereby a position on the scale of an instrument is identified with the magnitude of the signal (or input force) actuating the instrument.

Anemometer whicb measures wind speed by measuring the degree of cooling of a metal wire heated by an electric current. A type of cooling power anemometer.

A photometer which measures the intensity of radiation as a function of the frequency (or wavelength) of the radiation.

United Kingdom forecast model. (Available via AccuWeather.com Professional.)

See ceilometer.

A graphical representation of a frequency distribution. The range of the variable is divided into class intervals for which the frequency of occurrence is represented by a rectangular column. The height of the column is proportional to the frequency of ob ...

A measure of long-term precipitation effectiveness. The ratio of the normal annual rainfall to the normal annual evaporation.

Cathode Ray Tube. A display element, consisting of a vacuum tube and screen, used with computers.

Same as aneroid barometer. Holostelic means wholly made of solids, while aneroid means devoid of liquid.

See hook gauge.

See constant-level balloon.

Wind with a speed below 1 knot (1 mph); Beaufort scale number 0.

An instrument consisting of a series of graduated cylinders possessing selective collection efficiencies. It is used for the measurement of quantities relating to the size distribution of cloud droplets.

A thermoelectric thermometer used for measuring air temperature. The name is derived from the fact that the reference thermocouple is placed in an insulated bottle.

The change in barometric pressure within a specified period of time (typically 3 hours for meteorological observations).