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.

A flower-like diagram indicating the relative frequencies of different wind directions for a given station and period of time.

Wind with a speed between 22 and 27 knots (25 and 31 mph); Beaufort scale number 6.

An anemometer which measures wind speed in terms of the drag which the wind exerts on a solid body. See bridled-cup anemometer, normal-plate anemometer, pendulum anemometer.

The statement that the viscosity of air is independent of the density of air.

An instrument for determining the direction from which radio waves approach a receiver. It may consist of a manually operated direction indicator, or it may use a servo system to position the antenna automatically in the direction of the incident waves.

National Centers for Environmental Prediction. Central computer and communications facility of the National Weather Service; located in Washington, DC.

Same as an upper air observation, but commonly used to refer to a single complete radiosonde observation.

Any one of a family of circular arcs consisting of concentric colored bands, arranged from red on the inside to blue on the outside, which may be seen on a "sheet" of water drops (rain, fog, spray). The most common of the many possible is the primary rain ...

That horizontal wind velocity at which the Coriolis acceleration exactly balances the horizontal pressure force. It is directed along contour lines or isobars.

A reflecting type telescope with a 45

Conditions to which a device is subjected, not including the variable measured by the device. See normal operating conditions, reference operating conditions.

Sustained winds greater than or equal to 40 mph or gust greater than or equal to 58 mph.

A sunshine recorder of the type in which the time scale is supplied by the motion of the sun. It consists of two opaque metal semi-cylinders mounted with their curved surfaces facing each other. Each of the semi-cylinders has a short narrow slit in its fl ...

variable audio-modulated radiosonde developed at the Bureau of Standards and used by the United States weather services.

Meteorological information issued by a watch office concerning the occurrence or forecast of weather phenomena which may affect the safety of aircraft operations.

See ceilometer.

One of several constant-pressure levels in the atmosphere for which a complete evaluation of data derived from upper air observations is required.

An atmometer consisting of a porous porcelain or ceramic container connected to a calibrated reservoir filled with distilled water. Evaporation is determined by the depletion of water in the reservoir.

The temperature at which all three phases of a substance can exist in equilibrium. This temperature occurs at only one pressure. The triple-point of water is 273.16 K and is the basis of the Kelvin scale.