The difference between the input quantity applied to a measuring instrument and the output quantity indicated by the instrument. The inaccuracy of an instrument is equal to the sum of its instrument error and its uncertainty.

Radiation coming from the solid angle of the sun's disc, as opposed to diffuse sky radiation, effective terrestrial radiation, or radiation from any other source. Direct solar radiation is measured by pyrheliometers.

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

See mote.

A continuous-recording barometer.

A graphical representation of stage or discharge at a point on a stream as a function of time.

Abbreviation for binary digit. The smallest unit of information, equal to one binary decision, i.e. 1/0, on/off, yes/no.

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.

Ragged low clouds, usually stratus fractus. Most often applied when such clouds are moving rapidly beneath a layer of nimbostratus.

A unit of heat originally defined as the amount of heat required to raise the temperature of water through one degree centigrade (the gram-calorie or small calorie), but this proved to be insufficiently precise. The 15

A method of winds aloft observation essentially the same as a pilot balloon observation except the height data is derived from the radiosonde observation rather than from assumed ascension rates.

An instrument which measures the instantaneous rate at which rain is falling on a given surface. Also called a rate-of-rainfall gauge.

A class of instruments employed to determine the electric potential at a point in the atmosphere, and ultimately the atmospheric electric field.

A refraction phenomenon similar to a parahelion, but occurring generally at a distance of 120

A sudden brief increase in the speed of the wind, followed by a lull or slackening. Compare to peak gust.

The water volume within a specified portion of a stream channel.

Name given to the unit of pressure in the International System of Units (SI). Equal to 1 newton/meter2 or 0.01 millibar.

A liquid-in-metal thermometer in which mercury is enclosed in a steel envelope. The change in internal pressure caused by the temperature variation is measured by a Bourdon tube which is connected to the mercury by a capillary tube. This instrument is hig ...

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.

An instrument, for the recording of two or more meteorological parameters, in which the ventilation is provided by a suction fan.