A type of modulation in which the frequency of a continuous radio carrier wave is varied in accordance with the properties of a second (modulating) wave.

A general term for instruments designed to measure the speed or force of the wind.

Central Processing Unit. The part of a computer which controls and directs all functions.

A unit of luminous flux. The lumen is equal to the luminous flux radiated into a unit solid angle (steradian) from a small source having a luminous intensity of one candle. An ideal source possessing an intensity of one candle in every direction would rad ...

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

A class of rain gauge in which the level of the collected rain water is measured by the position of a float resting on the surface of the water.

A flower-like diagram indicating the relative frequencies of different wind directions for a given station and period of time.

February 2nd. In American folklore, a day that is popularly supposed to provide the key to the weather for the remainder of the winter. Specifically, if the ground-hog upon emerging from its hole casts a shadow, it will return underground, thereby forebod ...

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 device used to hold liquid-in-glass maximum and minimum thermometers in the proper recording position inside an instrument shelter, and to permit them to be read and reset. See Townsend support.

A standard interface between a computer input/output port and a peripheral device. Signal properties including time duration, voltage. and current, are specified by the Electronic Industries Association.

A type of cyanometer. an instrument used to measure the blueness of the sky. The Linke-scale is simply a set of eight cards of different standardized shades of blue. They are evenly numbered 2 to 26. The odd numbers are used by the observer if he or she j ...

Downward-facing pyranometer used for measuring reflected solar radiation.

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

A line of equal or constant temperature.

A line of equal or constant pressure.

The process of modifying some characteristic of a wave (the carrier) so that it varies in step with the instantaneous value of another wave (the modulating wave) in order to transmit a message. The modified characteristic may be frequency, phase, and/or a ...

A measure of the intensity of gusts given by the ratio of the total range of wind speed between gusts and the intermediate periods of lighter wind to the mean wind speed, averaged over both gusts and lulls.

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