A sudden brief increase in the speed of the wind, followed by a lull or slackening. Compare to peak gust.

Similar to the spectroheliograph, but used for visual instead of photographic purposes.

Precipitation composed of white or translucent ice crystals, chiefly in complex branched hexagonal forms.

A thermopile used in some types of radiation instruments. See solarimeter.

An instrument for determining the degree of polarization of light. See photopolarimeter.

Of or pertaining to rain.

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 ...

The downward flux of atmospheric radiation passing through a given level surface, usually taken as the earth's surface. This result of infrared (long-wave) absorption and reemission by the atmosphere is the principal factor in the greenhouse effect.

A numbering system using a base number of 2 and having only two digits: 0 and 1. The fundamental system of representing information with electrical pulses.

A measure of long-term precipitation effectiveness. The ratio of the normal annual rainfall to the normal annual evaporation.

A measure of luminous flux remaining in a light beam after it has passed through a specified distance of the atmosphere.

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

Abbreviation for visual flight rules, but commonly used to refer to the relatively favorable weather and/or flight conditions to which these rules apply.

Force wind-Wind with a speed above 64 knots (73 mph); Beaufort scale numbers 12 through 17.

The process of modifying some characteristic of a wave (the carrier) so that it varies in step with the instantaneous value of another wave (the modulating wave) in order to transmit a message. The modified characteristic may be frequency, phase, and/or a ...

The difference between the outgoing infrared terrestrial radiation of the earth's surface and the downcoming infrared counterradiation from the atmosphere.

A line drawn through all points on a map having the same amount of cloudiness.

General name for an instrument designed to measure the vertical component of the wind speed. See anemoclinometer.

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 ...

An absolute instrument developed by K. Angstrom for the measurement of direct solar radiation. The radiation receiver station consists of two identical manganin strips whose temperatures are measured by attached thermocouples. One of the strips is shaded, ...