A sunshine recorder of the type in which the time scale is supplied by a chronograph. It consists of two bulbs, one of which is blackened, which communicate through a glass tube of small diameter. The tube is partially filled with mercury and contains two ...

A balloon-borne instrument for the simultaneous measurement and transmission of meteorological data. It includes transducers for the measurement of pressure, temperature, and humidity; a modulator for the conversion of the output of the transducers to a q ...

The intensity (flux per unit solid angle) of visible radiation weighted to take into account the variable response of the human eye as a function of the wavelength of light. Usually expressed in candles.

A seasonal wind of persistent direction, characterized by a pronounced change in direction between seasons.

Precipitation composed of liquid water drops more than 0.5 mm in diameter, failing in relatively straight, but not necessarily vertical, paths. Compare to drizzle.

That temperature at which, in a specified latitude, the reading of a particular barometer requires no temperature or latitude correction.

Fine dust or salt particles dispersed through a portion of the atmosphere; a type of lithometer. The particles are so small they cannot be felt or seen with the naked eye. Many haze formations are caused by the presence of an abundance of condensation nuc ...

National Centers for Environmental Prediction. Central computer and communications facility of the National Weather Service; located in Washington, DC.

A hydrometeor consisting of a visible aggregate of minute water and/or ice particles in the atmosphere above the earth's surface. Cloud differs from fog only in that the latter is, by definition, in contact with the earth's surface.

In general, any self-recording instrument carried aloft by any means to obtain meteorological data.

A continuous-recording barometer.

Temperarure at which a liquid solidifies under any given set of conditions. It may or may not be the same as the melting point or the more rigidly defined true freezing point or (for water) ice point.

In general, any object that reflects incident energy. Usually it is a device designed for specific reflection characteristics.

Any and all forms of water particles, liquid or solid, that fall from the atmosphere and reach the ground.

A unit of luminous flux. The lumen is equal to the luminous flux radiated into a unit solid angle (steradian) from a small source having a luminous intensity of one candle. An ideal source possessing an intensity of one candle in every direction would rad ...

An instrument designed to measure the effect of sunlight on evaporation from plant foliage. It consists of a porous clay atmometer whose surface has been blackened so that it absorbs radiant energy.

Closed, curved, flexible tube of elliptic cross section which is deformed, according to type, by variations of atmosphere spheric pressure or temperature and so provides a measurement of the particular parameter.

Situated on the side from which the wind blows.

The minimum temperature shown by a minimum thermometer exposed in an open situation with its bulb at the level of the tops of the grass blades of short turf.

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