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

An instrument for measuring the ultraviolet in solar and sky radiation.

A pyrheliometer of the bimetallic type used to measure the intensity of direct solar radiation.

A buoyant balloon rising freely in the atmosphere, as opposed to a captive balloon.

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

The time required for an instrument to registe 63.2% of a step change in the variable being measured.

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

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

A mercury-in-glass thermometer which records the temperature upon being inverted and retains its reading until being returned to the first position.

The lowest value of a measured quality at which a sensor meets its accuracy specification.

An instrument used to measure the water vapor content of the air. A type of hygrometer. It consists of a wet-bulb and a dry-bulb thermometer. See aspiration psychrometer, Assmann psychrometer. hygrodeik, sling psychrometer.

Amount of solar radiation incident, per unit area and time, on a surface which is perpendicular to the radiation and is situated at the outer limit of the atmosphere, the earth being at its mean distance from the sun. It equals approximately 2.00 ly/ min ...

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

A defective maximum thermometer of the liquid-inglass type in which the mercury flows too freely through the constriction. Such a thermometer will indicate a maximum temperature that is too low.

The total amount of water transferred to the atmosphere by evapotranspiration.

An atmometer which uses a filter paper disc as the evaporating element. The amount of water evaporated through the paper is read at the graduated tube reservoir.

A type of electrical thermometer in which the thermal element is a substance whose electrical resistance varies with the temperature. Such thermometers can be made with very short time constants and are capable of highly accurate measurements.

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 unit of energy equal to 1.356joules.

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