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

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

See Koschmieder's law.

A measure of the relative power, or of the relative values of two flux densities, especially of sound intensities and radar power densities. The decibel is derived from the less frequently used unit, the bel, named in honor of Alexander Graham Bell.

An instrument which measures evaporation by measuring the loss of water from a burette reservoir through a ceramic disc.

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.

The amount of precipitation captured by a rain gauge.

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

Very generally, any moving- stream of air. It has no particular technical connotation.

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

An automatic, recording cloud height indicator.

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

See aneroid capsule.

Operation mode of a communication circuit in which each end can transmit and receive, but not simultaneously.

A small anemometer with flat vanes which indicates the number of linear feet or meters of air which have passed the instrument during its exposure.

An ice coating with a consistency intermediate between glaze and rime.

Pertaining to measurements or devices in which the output varies continuously, i.e. voltage or rotation signals. Compare to digital.

A chronograph used to make a time-record of certain measured meteorological elements. The most common type, the triple register, records wind direction and speed, duration of sunshine, and amount of rainfall (sensed respectively by a contact anemometer, M ...

A mercury barometer in which the lower mercury surface is larger in area than the upper surface. The basic construction of a cistern barometer is as follows: A glass tube one meter in length, sealed at one end is filled with mercury, and then inverted. Th ...