The standard deviation (positive square-root of the variation) of the errors associated with physical measurements of an unknown quantity, or statistical estimates of an unknown parameter or of a random variable.

A thermometer consisting of a clock mechanism the speed of which is a function of temperature.

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

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.

Situated on the side from which the wind blows.

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.

See calorie.

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 ...

Same as windsock.

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

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

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 instrument designed to study small fluctuations of some quantity. The microbarograph is an example of a recording pressure variometer.

See radiosonde commutator.

The height of the cloud base above the local terrain.

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

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 ...

See feed.

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