Turbulence encountered by aircraft when flying through air space devoid of clouds. Thermals and wind shear are the main causes.

An instrument for measuring the difference between incoming and outgoing terrestrial radiation.

A device for measuring the frequency of occurrence of atmospherics whose intensity is greater than a predetermined level.

See sea-water thermometer, reversing thermometer.

An instrument used to measure changes in the level of the water in an evaporation pan. The gauge is normally placed in a Stillwell and adjusted so that the point of the hook just breaks the water surface. The change in water level is read on the attached ...

Precipitation of very small, white opaque particles of ice, fairly flat or elongated, with diameters less than 1 mm. The solid equivalent of drizzle.

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

The change in a performance characteristic caused by a change in a specified operating condition from reference operating condition, all other conditions being held within the limits of reference operating conditions.

A thermoelectric thermometer used for measuring air temperature. The name is derived from the fact that the reference thermocouple is placed in an insulated bottle.

Precipitation of white, opaque, spherical or conical ice particles that are crisp and easily crushed and that have diameters of 2 to 5 mm.

The general term for anemometers operating on the principle that the heat transfer to air from an object at an elevated temperature is a function of the air speed. Examples are the hot-wire anemometer and the katathermometer.

The difference between temperature measurements taken at two significant levels above the ground. Temperatures at 10 and 40 meters are commonly used.

Same as pitot tube.

Frequency Shift Keying. A form of frequency modulation of a data signal performed by a modem for transmission over dedicated wire or phone lines.

The range of operating conditions within which a device is designed to operate and for which operating influences are stated. See operating conditions, reference operating conditions.

A measurement of atmospheric conditions aloft, above the effective range of a surface weather observation. Elements evaluated include temperature, humidity, pressure, wind speed, and wind direction.

An instrument used to measure the water vapor content of the air.

Video Display Terminal. An input and display device which includes a keyboard and a screen and allows a human to communicate with a computer.

A general name for instruments which detect the presence of (but do not necessarily measure) small electrical charges by electrostatic means. Compare to electrometer.

A semiconductor which exhibits rapid and extremely large changes in resistance for relatively small changes in temperature.