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 inert gas. An element found in the atmosphere to the extent of only 0.000114 percent by volume. Its molecular weight is 83.7.

The limiting values of ceiling, visibility, and wind, or runway visual range, established as safety minimum for aircraft landings and take-offs.

An instrument for measuring the intensity of direct solar radiation at normal incidence. See Angstrom compensation pyrheliometer, Eppley pyrheliometer, Michaelson actinograph. silver- disc pyrheliometer, spectropyrheliometer, waterflow pyrheliometer.

Automated Local Evaluation in Real Time. Network of automatic rain gauges that transmit via VHF radio link when precipitation occurs. Some sites are also equipped with other sensors such as temperature, wind, pressure, river stage or tide level. More info ...

The height at which the maximum wind speed occurs, determined in a winds-aloft observation.

The indicating part of an instrument. For example, the hand of a watch or the meniscus of a mercury column.

Same as balloon cover.

Strong winds concentrated within a narrow band in the atmosphere. The jet stream often "steers" surface features such as front and low pressure systems.

Old snow that has become granular and compacted as a result of melting and refreezing.

An up slope wind due to local surface heating. Opposite of katabatic wind.

See bimetallic thermometer.

Radio Direction Finder.

An instrument, located at the surface observing station, which is used to record the data presented by a radiosonde aloft.

Wind with a speed between 4 and 27 knots (4 and 31 mph); Beaufort scale numbers 2 through 6.

A captive balloon used to maintain meteorological equipment aloft at approximately a constant height. The kytoon is streamlined and combines the aerodynamic properties of a balloon and a kite.

A direct-vision nephoscope which is constructed in the following manner: a comb consisting of a crosspiece containing equispaced vertical rods is attached to one end of a column eight to ten feet long and is supported on a mounting that is free to rotate ...

General name for an instrument which measures the evaporation rate of water into the atmosphere. See clay atmometer, evaporation pan, evapotranspirometer, Livingston sphere, Piche evaporimeter, radio atmometer.

Fine dust or salt particles dispersed through a portion of the atmosphere; a type of lithometer. The particles are so small they cannot be felt or seen with the naked eye. Many haze formations are caused by the presence of an abundance of condensation nuc ...

Winds from the four cardinal points of the compass; that is, north, east, south, and west winds.