Abbreviation for Instrument Flight Rules, but commonly used to refer to the weather and/or flight conditions to which these rules apply, i.e. low visibility.

A form of data transmission in which the bits of each character are all sent simultaneously, resulting in extremely fast communication but requiring a communication path for each bit. Compare to serial data transmission.

An instrument for collecting liquid water from the atmosphere.

A coating of ice, generally clear and smooth. formed by the freezing of supercooled water on a surface.

Not a linear function of the relevant variables.

A direct-vision nephoscope constructed in the following manner: A grid-work of bars is mounted horizontally on the end of a vertical column and made free to rotate about the vertical axis. The observer rotates the grid and adjusts his or her position unti ...

A precipitation amount of less than 0.005 inches. Also, the record made by any self-registering instrument.

Particle on which the freezing of water occurs.

The change in the measured transducer output caused by changes in ambient temperature. Usually expressed a percentage of full scale.

A pointed device which indicates the amount of resistance encountered when it is forced into a material such as snow or soil. See ram penetrometer.

An instrument, dropped from high attitude and carried by a stable parachute. used to measure the vertical component of turbulence aloft.

A type of cistern barometer in which the level of mercury in the cistern is adjusted to the zero point of the scale before each reading.

General name for an instrument which measures the evaporation rate of water into the atmosphere. See clay atmometer, evaporation pan, evapotranspirometer, Livingston sphere, Piche evaporimeter, radio atmometer.

A type of cooling-power anemometer based upon the principle that the time constant of a thermometer is a function of its ventilation.

See photometer.

Same as luminous intensity.

A balloon designed to float at a constant pressure level. This may be accomplished by a pressure valve which controls the release of ballast so as to maintain flight above a selected pressure level until the supply of ballast is exhausted. See Moby Dick b ...

The value of the quantity measured, as indicated or otherwise provided by a measuring instrument.

Automated Weather Observing Station. A self-contained weather station designed to make aviation weather observations without operator involvement.

The distance that an observer can see vertically into a surface-based obscuring phenomenon such as fog, rain, or snow. The distance estimate must be based upon ceiling balloon ascensions or ceiling light projector measurements.