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 ...

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

Formation of a single water drop by the union of two or more colliding drops.

A curve showing the variation of temperature with height in the free air. See lapse rate.

Determined by weighing a special type of wooden stick that has been exposed in the woods, its weight being proportional to its contained water.

See radar theodolite, radio direction-finder.

A thermometer whose sensitive element has been made to resemble a black body by covering it with lamp black. The thermometer is placed in an evacuated transparent chamber which is maintained at a constant temperature. The instrument responds to insolation ...

The frequency of a carrier wave.

Same as dropsonde.

National Weather Service. Administered by the U.S. Department of Commerce.

A type of directional antenna used on some types of radar and radio equipment consisting of an array of elemental, single- wire dipole antennas and reflectors.

Atmospheric layer throughout which there is no change of temperature with height, i.e. a zero lapse rate.

An area of low barometric pressure, with its attendant system of winds. Also called a depression or cyclone.

The difference between the solar radiation directed downward and upward; net flux of solar radiation.

Anemometer which measures wind speed by measuring the degree of cooling of a metal film heated by an electric current. A type of cooling-power anemometer.

Eluding precise prediction, completely irregular.

A wind (or component thereof) directed down the slope of an incline and caused by greater air density near the slope than at the same levels some distance horizontally from the slope. Also called drainage wind and sometimes called katabatic wind.

See gain.

A generic term for any machine that enables a human being to communicate with a computer.

A photometric unit of illuminance or illumination equal to one lumen per square meter