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

The total electromagnetic radiation emitted by the sun. About 99.9 percent of its energy output falls within the wavelength interval from 0. 15 microns to 4.0 microns, with peak intensity near 0.47 microns. About one-half of the total energy in the solar ...

The physical exposure of an instrument. The effect of immediate environment upon the representativeness of the measurements obtained by meteorological instruments is considerable and not always correctable. The purpose of the instrument shelter is to prov ...

The boundary between the troposphere and stratosphere, usually characterized by an abrupt change in lapse rate. Its height varies from 10 to 20 km. Regions above the tropopause have greater atmospheric stability than regions below.

The mean difference between the readings of a given instrument and those of a standard instrument.

Lowest altitude in the atmosphere over a given location at which the air temperature is 0

Solar radiation of selected wavelengths.

Same as water year.

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 rate of decrease of pressure per unit distance at a fixed time.

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

The most common of the principal rainbow phenomena, which appears as an arc of about 42

A precipitation amount of less than 0.005 inches. Also, the record made by any self-registering instrument.

Pertaining to rain, or more broadly, to precipitation.

A self-recording psychrometer.

A mercury barometer arranged so that the position of the upper or lower meniscus may be measured photographically. In one design the image of the meniscus is formed on a rotating drum covered with sensitized paper so that a continuous record of pressure a ...

A thermometer based upon the principle that the velocity of a sound wave is a function of the temperature of the medium through which it passes. Sonic thermometers possess very short time-constants and eliminate radiation error.

Determination of the total amount of snow covering a watershed or a given region. Both depth and water content of the snow may be measured, and the results may be used to predict the amount of water that will be available after melting.

A unit of luminance or brightness equal to 1/d candles per foot'.

A navigational aid used to facilitate the landing of an aircraft at an airport in instrument weather, i.e. low visibility.