The lowest temperature that can be obtained on a wet-bulb thermometer in any given sample of air. Obtained by evaporation of water (or ice) from the muslin wick. Used in computing dew point and relative humidity.

An instrument whose calibration can be determined by means of simple physical measurements on the instrument. Compare to secondary instrument.

Operation mode of a communication circuit in which each end can transmit and receive, but not simultaneously.

Moisture contained in the soil above the water table, including water vapor which is present in the soil pores. In some cases this term refers strictly to the humidity contained in the root zone of plants.

Thermometer in which the difference in the rates of expansion with temperature of a liquid and its receptacle is used as a measure of the temperature. The liquid used may be ethyl alcohol, toluene, petroleum, or mercury.

Apparatus in which radar techniques are used to determine the range, elevation, and azimuth of a balloonborne target, to computer upper-air wind data. It is a type of rawin system.

A cover which fits over a large inflated balloon to facilitate handling in high or gusty winds.

An atmometer consisting of a porous porcelain or ceramic container connected to a calibrated reservoir filled with distilled water. Evaporation is determined by the depletion of water in the reservoir.

The stage, on a fixed river gauge, corresponding to the top of the lowest banks within the reach for which the gauge is used as an index. Compare to flood stage.

A pressure-operated switching device used in a radiosonde. In operation, the expansion of an aneroid capsule causes an electrical contact to scan a radiosonde commutator composed of conductors separated by insulators.

In folklore, a name for rain.

The record made by a hygrograph.

A measure, proposed by Angstrom, of the precipitation effectiveness of a region.

Name sometimes given to a transmissometer.

Same as ceiling light.

A small balloon, loaded with ballast and inflated so that it will explode at a predetermined altitude, which is attached to a larger balloon.

Generally, a measure of the departure of the mean daily temperature from a given standard, one degree day for each degree (

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

The transducer of any hygrometer, i.e. that part of a hygrometer that quantitatively "senses" atmospheric water vapor.

Wind with a speed between 41 and 47 knots (47 and 54 mph); Beaufort scale number 9.