A measurement of atmospheric conditions aloft, above the effective range of a surface weather observation. Elements evaluated include temperature, humidity, pressure, wind speed, and wind direction.

An instrument designed to record the duration of sunshine at a given location without regard to intensity. See Campbell- Stokes recorder, Jordan sunshine recorder, Marvin sunshine recorder, Pers sunshine recorder.

An instrument for measuring the frost point of the atmosphere.

The unit of acceleration in the centimeter-gram-second system of units, equal to one cm per sec2. Commonly used in gravimetry.

A hygrometer in which the sensitive element is a strand or strands of human hair, the length of which is a function of the relative humidity of the air.

in folklore, a name for fire.

A type of wind vane having a split or V-shaped tail. The apex orients itself to the direction of the wind.

Same as altimeter setting.

A river gauge in which a weight suspended on a wire is lowered to the water surface from a bridge or other overhead structure to measure the distance from a point of known elevation to the water surface.

The distance or length of flow of the air past a point during a given interval of time.

The atmospheric pressure at mean sea level either directly measured by stations at sea level or empirically determined from the station pressure and temperature by stations not at sea level. Used as a common reference for analyses of surface pressure patt ...

The amount of moisture which, if available, would be removed from a given land area by evapotranspiration. Expressed in units of water depth.

General name for an instrument which measures the evaporation rate of water into the atmosphere. See clay atmometer, evaporation pan, evapotranspirometer, Livingston sphere, Piche evaporimeter, radio atmometer.

Abbreviation for radio frequency.

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

An instrument used to determine atmospheric pressure or elevation by observing the boiling point of water or both liquids. The sensitivity of the hypsometer increases with decreasing pressure, making it more useful for high altitude work.

See river basin.

The process by which water in plants is transferred as water vapor to the atmosphere. Also, the amount of water so transferred.

An instrument of the aspiration condenser type which measures the concentration and mobility of small ions.

Winds from the four cardinal points of the compass; that is, north, east, south, and west winds.