climatology and meteorology

anticyclonic circulation

system of air movements (atmospheric circulation) associated with an anticyclone, which is clockwise in the northern hemisphere and counter-clockwise in the southern hemisphere.

anticyclone

area of increased atmospheric pressure relative to surrounding pressure field in the atmosphere; outlined by closed isobars on a synoptic surface chart, and by closed contours on a constant-pressure chart; used interchangeably with high..

anomaly

deviation of a meteorological quantity value in a given region from the normal (mean) value for the same period.

aneroid barometer

an instrument for measuring atmospheric pressure; it is constructed on the following principles: an aneroid capsule (vidie capsule, which is a thin, disk-shaped box or capsule, usually metallic) is partially evacuated of gas, and is restrained from collapsing by an external or internal spring; the deflection of the spring will be nearly proportional to the difference between the internal and external pressures; magnification of the spring deflection is obtained both by connecting capsules in series and by mechanical linkages.

anemorumbometer

a Russian anemometer combined with a vane to determine the wind direction.

anemorumbograph

a Russian anemograph (recording anemometer) which is equipped with a device to record the wind direction in addition to wind speed.

anemometer

an instrument which measures wind speed or wind speed and direction; a cup anemometer measures the wind speed from the speed of rotation of a windmill which consist of 3 or 4 hemispherical or conical cups, each fixed to the ends of horizontal arms attached to a vertical axis; a byram anemometer is a variety of the cup anemometer; a counting anemometer has cups or a fan whose rotation is transmitted to a technical counter which integrates directly the air movement speed; a hand anemometer is small portable anemometer held at arm's length by an observer making a wind speed measurement; a pressure tube anemometer (dines anemometer) is an instrument which derives wind speed from measurements of the dynamic wind pressures - wind blowing into a tube develops a pressure greater than the static pressure, while wind blowing across a tube develops a pressure less than the static, this pressure difference is proportional to the square of the wind speed.

Azores high

the semipermanent subtropical high over the North Atlantic Ocean, especially when it is located over the eastern part of the ocean; the same high over the western part of the Atlantic is called the Bermuda high; on mean charts of sea level pressure, this high is one of the primary centers of action in northern latitudes.

arctic zone

(1) geographically, the area north of the arctic circle (66° 34′ N) (2) (same as tundra) biogeographically, the area extending northward from the arctic tree line; also used for the level above the timber line in mountains.

arctic tree line

the northern limit of tree growth; the sinuous boundary between tundra and boreal forest; taken by many to delineate the actual southern boundary of the arctic zone.

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