Abbreviation for binary digit. The smallest unit of information, equal to one binary decision, i.e. 1/0, on/off, yes/no.

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

The upper surface of a column of liquid.

A thermometer which utilizes the thermal properties of gas. There are two forms of this instrument: (a) a type in which the gas is kept at constant volume, and pressure is the thermometric property, and (b) a type in which the gas is kept at constant pres ...

A liquid-in-glass or liquid-in-metal thermometer using mercury as the liquid.

An element that can control current without moving parts, heated filaments, or vacuum gaps.

Radiation coming from the solid angle of the sun's disc, as opposed to diffuse sky radiation, effective terrestrial radiation, or radiation from any other source. Direct solar radiation is measured by pyrheliometers.

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

See constant-level balloon.

Solar and terrestrial radiation directed upward (away From the earth's surface); outgoing radiation.

A special type of radar target, usually a comer reflector, tied beneath a free balloon and designed to be an efficient reflector of radio energy.

A rainbow seen in the spray of the ocean. It is optically the same phenomenon as the ordinary rainbow.

The visibility along an identified runway, determined from a specified point on the runway with the observer facing in the same direction as a pilot using the runway. Compare to runway visible range.

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

Generally, a measure of the departure of the mean daily temperature from a given standard, one degree day for each degree (

A unit of energy equal to 101 ergs or to 0.2389 calories.

Meteorological information issued by a watch office concerning the occurrence or forecast of weather phenomena which may affect the safety of aircraft operations.

The succession of stages through which water passes on the ground and in the atmosphere: evaporation from land or bodies of water, condensation to form clouds, precipitation, accumulation in the soil or in bodies of water, and re-evaporation.

A liquid-in-metal thermometer in which mercury is enclosed in a steel envelope. The change in internal pressure caused by the temperature variation is measured by a Bourdon tube which is connected to the mercury by a capillary tube. This instrument is hig ...

An addition to a rawinsonde system which allows determination of the slant range to the radiosonde.