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 the measurement of both solar and terrestrial radiation.

Same as balloon cover.

pattern barometer-Mercurial barometer with a fixed scale and cistern and which therefore requires only one adjustment before each reading.

A wind blowing in the same direction as the heading of a moving object. thus assisting the object's intended progress. The opposite of a head wind.

A type of climatic diagram whose coordinates are some form of temperature vs. a form of humidity or precipitation.

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 ...

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.

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

See bimetallic thermometer.

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

Radio Direction Finder.

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 ...

A unit of energy per unit area commonly employed in radiation theory. Equal to one gram-calorie per square centimeter.

Instrument for measuring the depth to which the soil is frozen.

An ion counter of the aspiration condenser type, used for the measurement of the concentration and mobility of small ions in the atmosphere.

The inaccuracy that the manufacturer permits when the unit is calibrated in the factory.

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 ...

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

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