A large plastic constant-level balloon for duration flying (in excess of 24 hours) at altitudes above 40,000 feet, used for the determination of wind fields and the measurement of upper atmospheric parameters.

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

The humidity transducinu element in a Diamond-Hinman radiosonde. Also called electrolytic strip.

A polarimeter utilizing a Wollaston prism as a polarizer and a Nicol prism as an analyzer.

An elongated area of relatively low atmospheric pressure. Usually associated with and most clearly identified as an area of maximum cyclonic curvature of the wind flow. The opposite of a ridge.

An effect noted primarily in wet snow conditions when snow clings to the sides of a precipitation gauge and gradually accumulates until the gauge orifice is capped with accumulated snow. This effect can be minimized by using large collectors, and wind scr ...

A graphical representation of stage or discharge at a point on a stream as a function of time.

A systematic summary of the terms (inflow, outflow, and storage) of the storage equation as applied to the computation of soil-moisture changes, ground-water changes, etc. An evaluation of the hydrologic balance of an area. Also called basin accounting, w ...

A line of equal or constant temperature.

The amount of sky covered or concealed by clouds or obscuring phenomena. It is reported in tenths, so that 0.0 indicates a clear sky and 1.0 (or 10/10) indicates a completely covered sky. The following classifications are used in aviation weather observat ...

Same as parhelion.

A radiosonde which is dropped by parachute from an aircraft for the purpose of obtaining soundings of the atmosphere below.

An instrument for measuring the intensity of light or the relative intensity of a pair of lights. Also called an illuminometer. If the instrument is designed to measure the intensity of light as a function of wavelength, it is called a spectrophotometer. ...

A rotation anemometer which has a horizontal axis upon which helicoidal shaped vanes are mounted. See windmill anemometer.

A photometer which measures the intensity of radiation as a function of the frequency (or wavelength) of the radiation.

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

The atmospheric pressure computed using station elevation as the reference datum level. Station pressure is usually the base value from which sea level pressure and altimeter setting are determined.

A synoptic code approved by the World Meteorological Organization in which the observable meteorological elements are encoded and transmitted in "words" of five numerical digits length. Often abbreviated synoptic code.

A line drawn through geographical points having the same duration of sunshine (or other function of solar radiation) during a given interval of time.

Same as water year.