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.

In physics, any process in which the flux density (or power, amplitude, intensity, illuminance, etc.) of a "parallel beam" of energy decreases with increasing distance from the source. Attenuation is always due to the action of the transmitting medium its ...

Same as windsock.

An instrument for measuring the pressure of gases and vapors. A mercury barometer is a type of manometer.

See hydrologic accounting.

A device for measuring sea-surface waves. It consists of a weighted pole below which a disk is suspended at a depth sufficiently deep for the wave motion associated with deepwater waves to be negligible. The pole will then remain nearly as if anchored to ...

Generally, an instrument designed to measure or estimate the blueness of the sky. See Linke-scale.

The part of a measuring instrument which responds directly to changes in the environment.

A wave resulting from the action of wind on a water surface.

The difference between temperature measurements taken at two significant levels above the ground. Temperatures at 10 and 40 meters are commonly used.

Temperature to which absolutely dry air would have to be brought in order for it to have the same density as moist air, considered at the same pressure.

Air in motion relative to the surface of the earth. Almost exclusively used to denote the horizontal component.

A form of data transmission in which the bits of each character are sent one at a time along a single communication path. Compare to parallel data transmission.

An increase in the central pressure of a pressure system; opposite of a deepening. More commonly applied to a low rather than a high.

The state of the weather with respect to its effect upon the kindling and spreading of forest fires.

A white disk 12" or more in diameter which is lowered into the sea to estimate transparency of the water. The depths are noted at which it first disappears when lowered and reappears when raised.

A method of upper air observation consisting of an evaluation of the wind speed and direction, temperature, pressure, and humidity aloft by means of a balloon-borne radiosonde tracked by radar or a radio theodolite.

A photometer that measures the received intensity of a distance tight source.

A radiosonde whose carrier wave is modulated by audio-frequency signals whose frequency is controlled by the sensing elements of the instrument.

A rain gauge capable of measuring very small amounts of precipitation. Also called micropluviometer, trace recorder.