A scale with the ice point at zero degrees and the boiling point of water at 80 degrees, with pressure of one atmosphere.

The nautical mile is closely related to the geographical mile which is defined as the length of one minute of arc on the earth's equator. By international agreement, the nautical mile is now defined as 1852 meters.

A measure of the attenuation due to scattering, of light as it traverses a medium containing scattering particles.

Ragged low clouds, usually stratus fractus. Most often applied when such clouds are moving rapidly beneath a layer of nimbostratus.

A general name for instruments which detect the presence of (but do not necessarily measure) small electrical charges by electrostatic means. Compare to electrometer.

A unit of power equal to one joule per second or 10' ergs per second.

A graphical device used for the determination of the speed of the geostrophic wind from the isobar or contour-line spacing on a synoptic chart.

In general, any object that reflects incident energy. Usually it is a device designed for specific reflection characteristics.

The condition of the atmosphere when the amount of water vapor present is the maximum possible at the existing temperature.

An old nautical term for mercury barometer.

Temperature to which absolutely dry air would have to be brought in order for it to have the same density as moist air, considered at the same pressure.

A vector term which includes both wind speed and wind direction.

See calorie.

A unit of energy defined as the heat required to raise the temperature of one pound of water one degree Fahrenheit. It is equal to 252.1 calories or to 1055 joules.

The total area drained by a river and its tributaries. Same as river basin.

Conditions to which a device is subjected, not including the variable measured by the device. See normal operating conditions, reference operating conditions.

The gravity flow of water within soil.

The range of operating conditions within which a device is designed to operate and for which operating influences are stated. See operating conditions, reference operating conditions.

Name given to the unit of pressure in the International System of Units (SI). Equal to 1 newton/meter2 or 0.01 millibar.

A radiosonde whose carrier wave is switched on and off in such a manner that the interval of time between the transmission of signals if a function of the magnitude of the meteorological elements being measured.