The value of atmospheric pressure to which the scale of a pressure altimeter is set so as to indicate airport elevation. The altimeter setting is included as part of an aviation weather observation.

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

The record of a barograph.

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.

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

A device used to hold liquid-in-glass maximum and minimum thermometers in the proper recording position inside an instrument shelter, and to permit them to be read and reset. See Townsend support.

Atmospheric layer throughout which there is no change of temperature with height, i.e. a zero lapse rate.

An atmometer which uses a filter paper disc as the evaporating element. The amount of water evaporated through the paper is read at the graduated tube reservoir.

A forecast of weather elements of particular interest to aviation; including ceiling, visibility, upper winds, icing, turbulence, precipitation types, and storms.

A calorimetric radiation instrument of historic interest used for the measurement of outgoing heat radiation from the earth during an interval of time. The time integration is performed by allowing the radiation to fall on an uninsulated vessel containing ...

Liquid water at temperatures colder than freezing.

A hydrostatic principle that pressure supplied to an enclosed fluid is transmitted undiminished to every portion of the fluid and to the walls of the containing vessel.

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.

Wind with a speed between 28 and 33 knots (32 and 38 mph); Beaufort scale number 7.

Same as radiation pattern. Anticyclone-An area of high atmospheric pressure which has a closed circulation that is anticyclonic (clockwise in northern hemisphere and counterclockwise in southern hemisphere).

A constant which describes the performance of a wind vane in response to a step change in wind direction. It is calculated from the relative amount of overshoot on two successive swings (half cycles) of a decaying oscillation. This specification is dimens ...

See gust and peak gust.

A current meter consisting of six conical cups, mounted around a vertical axis, which rotate and generate a signal with each rotation. Tail vanes and a heavy weight stabilize the instrument.

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

The array of indicating marks and figure in relation to which the position of an index is observed, i.e. a scale plate on a recorder.