A hydrometeor consisting of a visible aggregate of minute water droplets suspended in the atmosphere near the earth's surface. Fog differs from cloud only in that the base of fog is at the earth's surface while clouds are above the surface.

Pertaining to measurements or devices in which the output vanes in discrete steps, i.e. on-off or pulse signals. Compare to analog.

A type of pressure-tube anemometer, named after the inventor.

Similar to the spectroheliograph, but used for visual instead of photographic purposes.

The closeness of agreement among a number of consecutive output values measuring the same input value under the same operating conditions, approaching from the same direction. Usually measured as nonrepeatability but expressed as repeatability, a percenta ...

An instrument designed to record the duration of sunshine at a given location without regard to intensity. See Campbell- Stokes recorder, Jordan sunshine recorder, Marvin sunshine recorder, Pers sunshine recorder.

An aneroid barograph designed to record atmospheric pressure variations of very small magnitude.

The size of the area comprising a watershed or river basin. Also called catchment area.

An instrument used to measure the amount of dew formed on a given surface.

Anemometer which measures wind speed by measuring the degree of cooling of a metal film heated by an electric current. A type of cooling-power anemometer.

General term for any device that measures precipitation: principally a rain gauge or snow gauge.

See calorie.

Based upon damage patterns, classifies twisters into six categories of wind speed (F0 thru F5), ranging from 40 to 318 mph estimated wind speed.

An instrument consisting of a series of graduated cylinders possessing selective collection efficiencies. It is used for the measurement of quantities relating to the size distribution of cloud droplets.

The elevation of the water surface in a stream as measured by a river gauge with reference to some arbitrarily selected zero datum.

The combined processes by which water is transferred from the earth's surface to the atmosphere: evaporation of liquid or solid water plus transpiration from plants.

Rate of flow of water past a point in a stream, expressed as volume per unit time, i.e. cubic feet per second.

The sum of solar and terrestrial radiation.

A momentary decrease in the speed of the wind.

A vent used with pressure sensors to reduce the effect of wind on the pressure inlet. It is normally mounted remotely and connected to the sensor using airtight tubing.