A decrease in the central pressure of a pressure system. Usually applied to a low rather than to a high.

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.

General name for an instrument which measures the earth's magnetic field intensity.

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

Situated on the side from which the wind blows.

A radiosonde which transmits the indication of the meteorological sensing elements in the form of a code consisting of combinations of dots and dashes.

The atmospheric pressure at mean sea level either directly measured by stations at sea level or empirically determined from the station pressure and temperature by stations not at sea level. Used as a common reference for analyses of surface pressure patt ...

A clock-driven instrument mounting which automatically and continuously points in the direction of the sun. It is used with a pyrheliometera,hen continuous direct solar radiation measurements are required.

A rain gauge or array of rain gauges designed to measure the inclination and direction of falling rain.

See feed.

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 type of cloud height indicator which uses a searchlight to project vertically a narrow beam of light onto the cloud base. The height of the cloud is determined using a clinometer, located at a known distance from the ceiling light, to measure the angle ...

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

A very sensitive electrostatic electrometer for measuring small potential differences.

A large body of air having similar horizontal temperature and moisture characteristics.

The height of the cloud base above the local terrain.

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

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 ...

See radiosonde commutator.

A type of precipitation composed of unbranched crystals in the form of needles, columns, or plates. Usually has a very slight downward motion and may fall from a cloudless sky.