A measure of the attenuation due to scattering, of light as it traverses a medium containing scattering particles.

The meteorological visual range, which can be estimated from the average extinction coefficient using the Koschmieder equation.

See standard atmosphere.

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

Abbreviation for mean sea level.

A colorless and odorless gaseous element. The lightest and apparently the most abundant chemical element in the universe. However, it is found only in trace quantities in the observable portion of our atmosphere, only about 0.00005 percent by volume of dr ...

Negative Vorticity Advection.

Generic term for rapid variations in apparent position, brightness, or color of a distant luminous. object viewed through the atmosphere.

A line drawn through geographical points where a given seasonal biological event occurs on the same date.

Same as an upper air observation, but commonly used to refer to a single complete radiosonde observation.

in folklore, a name for fire.

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

The limiting values of ceiling, visibility, and wind, or runway visual range, established as safety minimum for aircraft landings and take-offs.

See captive balloon, ceiling balloon, constant-level balloon, free balloon, hurricane beacon, kytoon, Moby Dick balloon, pilot balloon, radiosonde balloon, rockoon, skyhook balloon, transosonde.

The process whereby a position on the scale of an instrument is identified with the magnitude of the signal (or input force) actuating the instrument.

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

An instrument for determining the direction of cloud motion. There are two basic designs of nephoscope, the directvision nephoscope and the mirror nephoscope.

A device for computing certain psychrometric data, usually the dew point and the relative humidity, from known values of the dry-bulb and wet-bulb temperatures and the atmospheric pressure. One type is the circular slide-rule form and, like the psychromet ...

The transducer of any hygrometer, i.e. that part of a hygrometer that quantitatively "senses" atmospheric water vapor.

In aviation terminology, route or terminal weather conditions of sufficiently low visibility to require the operation of aircraft under instrument flight rules.