The part of a measuring instrument which responds directly to changes in the environment.

A device that allows a terminal or computer at one location to communicate with a terminal or computer at a distant location via wire or phone lines.

Apparatus designed to measure and record the size distribution of raindrops as they occur in the atmosphere.

The intensity (flux per unit solid angle) of visible radiation weighted to take into account the variable response of the human eye as a function of the wavelength of light. Usually expressed in candles.

Frozen or partly frozen rain.

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

An instrument which measures the intensity of radiation by determining the amount of chemical change( or fluorescence produced by that radiation.

The atmospheric pressure at the level of the barometer. May or may not be the same as station pressure.

A hydrometeor consisting of a visible aggregate of minute water and/or ice particles in the atmosphere above the earth's surface. Cloud differs from fog only in that the latter is, by definition, in contact with the earth's surface.

A buoyant balloon kept from rising freely by means of a line secured to a point on the ground, as opposed to a free balloon. See kytoon.

Same as parhelion.

A hygrometer in which the sensitive element is a strand or strands of human hair, the length of which is a function of the relative humidity of the air.

Same as Aeolian.

A hygrometer in which the rotation of the hygrometric element is a function of humidity.

The average temperature of the air as indicated by a properly exposed thermometer for a given time period, usually a day, a month, or a year.

A component of the wind (often using Cartesian coordinates. i.e. X and Y wind vectors). Also, an arrow representing wind velocity, drawn to point in the direction of the wind and with a length proportional to wind speed.

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

The direction toward which the wind is blowing; with the wind.

Wind with a speed between 17 and 21 knots (19 and 24 mph); Beaufort scale number 5.

An instrument used for measuring the specific gravity of a liquid.