For a given cloud or cloud laver. the lowest level in the atmosphere at which the air contains a perceptible quantity of cloud particles.

The process in which incident radiation is retained by a substance. A further process always results from absorption.

Difference between the temperatures of the dry-bulb and the wet-bulb thermometers of a psychrometer.

Any emission of light at temperatures below that required for incandescence.

An instrument used to measure and record earthquake vibrations and other earth tremors.

See wind vane.

The total luminous flux received on a unit area of a given real or imaginary surface, expressed in such units as the foot-candle, lux, or phot.

Water vapor content of the air. See absolute humidity, dew point, mixing ratio, relative humidity, specific humidity.

Same as precipitation-evaporation ratio.

An evaporation pan in which the evaporation is measured from water in a pan floating in a larger body of water.

A system of estimating and reporting wind speed, originally based on the effect of various wind speeds on the amount of canvas that a full-rigged nineteenth century frigate could carry.

The level at which ice crystals and snowflakes melt as they descend through the atmosphere.

A type of atmometer. It is a pan used in the measurement of the evaporation of water into the atmosphere. The NWS Class A pan is a cylindrical container 48 inches in diameter and 10 inches deep.

An instrument used for the determination of the electrical conductivity of the atmosphere.

An instrument whose calibration is determined by comparison with an absolute instrument.

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

Thermodynamic change of state of a system in which there is transfer of heat across the boundaries of the system. Compare to adiabatic process.

The range of operating conditions of a device within which operating influences are negligible. The range is usually narrow. Reference operating conditions are the conditions under which reference performance is stated and the base from which the values o ...

A recording weight barometer.

A white disk 12" or more in diameter which is lowered into the sea to estimate transparency of the water. The depths are noted at which it first disappears when lowered and reappears when raised.