The ratio of the amount of electromagnetic radiation reflected by a body to the amount incipient upon it, commonly expressed as a percentage. The albedo is to be distinguished from the reflectivity, which refers to one specific wavelength.

Ragged low clouds, usually stratus fractus. Most often applied when such clouds are moving rapidly beneath a layer of nimbostratus.

The decrease of an atmospheric variable with height, the variable being temperature, unless otherwise specified.

Same as constant-level balloon.

Difference between the instantaneous wind velocity at a point and the mean wind velocity taken over a given time interval. Also called fluctuation velocity.

A general name for instruments which detect the presence of (but do not necessarily measure) small electrical charges by electrostatic means. Compare to electrometer.

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

A hygrometer which uses a transducing element whose electrical properties are a function of atmospheric water vapor content. The humidity strip and carbon-film hygrometer element are examples of such a transducer.

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

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

National Weather Service. Administered by the U.S. Department of Commerce.

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

Situated on the side from which the wind blows.

The maximum distance along the runway at which the runway lights are visible to a pilot at touchdown. Runway visual range may be determined by an observer located at the end of the runway, facing in the direction of landing, or by means of a transmissomet ...

Any one of numerous devices for the measurement of either speed alone or of both direction and speed (set and drift) in flowing water.

See evaporation pan.

The unit of force in the centimeter-gram-second system of physical units, i.e. one gm cm per sec2, equal to 7.233 x 10-5 poundal.

Infrared radiation emitted by or being propagated through the atmosphere.

In meteorology, a deflecting force acting on a body in motion and resulting from the earth's rotation. It deflects air currents to the right in the northern hemisphere and to the left in the southern hemisphere, thus having an effect on wind direction.

An evaluation, according to set procedures, of those weather elements which are most important for aircraft operations. Always includes cloud height or vertical visibility, sky cover, visibility, obstructions to vision, certain atmospheric phenomena, and ...