The greatest distance at which it is just possible to see and recognize with the unaided eye (1) in the daytime, a prominent dark object against the sky at the horizon, and (2) at night, a known, preferably unfocused, moderately intense light source.

A device that combines several separate communications signals into one and outputs them on a single line.

An addition to a rawinsonde system which allows determination of the slant range to the radiosonde.

Abbreviation for precipitation-evaporation quotient.

Radiation with wavelengths less than 4 microns.

Air in motion relative to the surface of the earth. Almost exclusively used to denote the horizontal component.

An absolute temperature scale with the ice point of pure water defined as 273.16 K. The size of the degree is the same as on the Celsius scale, and the zero point is absolute zero.

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

The downward flux of atmospheric radiation passing through a given level surface, usually taken as the earth's surface. This result of infrared (long-wave) absorption and reemission by the atmosphere is the principal factor in the greenhouse effect.

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.

Situated on the side from which the wind blows.

The older name for the Celsius temperature scale. Officially abandoned by international agreement in 1948, but still in common use.

Same as mercury barometer.

A severe weather condition characterized by low temperatures and strong winds bearing a great amount of snow, either falling or picked up from the ground.

Occupational Safety and Health Administration. A regulatory office of the U.S. Department of Labor.

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

An instrument, dropped from high attitude and carried by a stable parachute. used to measure the vertical component of turbulence aloft.

Same as atmometer.

Same as atmospheric pressure.

An instrument for the measurement of the net flux of downward and upward total (solar and terrestrial) radiation through a horizontal surface.