An instrument for measuring the pressure of the atmosphere. The two principle types are aneroid and mercurial.

Precipitation composed of white or translucent ice crystals, chiefly in complex branched hexagonal forms.

A modification of the dew cell used in radiosonde equipment.

An aneroid barometer arranged so that the deflection of the aneroid capsule actuates a pen which graphs a record on a rotating drum. Sometimes called aneroidograph.

A type of cistern barometer in which the level of mercury in the cistern is adjusted to the zero point of the scale before each reading.

A unit of energy equal to 1.356joules.

A thermograph in which ventilation is provided by a suction fan.

An area of low atmospheric pressure which has a closed circulation that is cyclonic (counterclockwise in northern hemisphere and clockwise in southern hemisphere).

Air in motion relative to the surface of the earth. Almost exclusively used to denote the horizontal component.

A recording weight barometer.

The wind speed and direction at various levels in the atmosphere above the level reached by surface weather observations.

A type of anemometer in which the rotation of an element serves to measure the wind. Rotation anemometers are divided into two classes; those in which the axis of rotation is horizontal, such as the windmill anemometer, and those in which the axis of rota ...

A box-like structure designed to protect certain meteorological instruments from exposure to direct sunlight, precipitation, and condensation, while at the same time providing adequate ventilation. Instrument shelters are painted white, have louvered side ...

An instrument which automatically records the voltage applied to it, as a function of time.

An absolute temperature scale with the ice point of pure water defined as 273.16 K. The size of the degree is the same as on the Celsius scale, and the zero point is absolute zero.

An anemometer in which the sensor rotation is transmitted to a mechanical counter which directly integrates the air movement past the sensor. Used to determine total air passage (wind run). Average wind speed can be calculated from the difference between ...

Same as water year.

Board that holds graph paper on which is plotted information obtained from a pilot-balloon observation.

Ice crystal deposits formed by sublimation (conversion of water vapor directly to ice) when temperature and dew point are below freezing.

Automated Weather Observing Station. A self-contained weather station designed to make aviation weather observations without operator involvement.