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air pressure

the pressure exerted by the mass of air above a given point, usually expressed in millibars, inches of mercury, or in hectopascals

millibar

a unit for expressing atmospheric pressure

standard atmospheric pressure

A pressure of 1013.25 mb, 29.92 inHg, 760 mmHg, 14.7 lbpsi, or 1013.25 hectopascals

barometer

an instrument that measures atmospheric pressure.

mercury barometer

a type of barometer that uses mercury to measure atmospheric pressure. The height of the mercury column is a measure of atmospheric pressure.

aneroid barometer

an instrument designed to measure atmospheric pressure. Contains no liquid.

station pressure

the actual pressure computed at the observing sttion

sea-level pressure

the atmospheric pressure at mean sea level

isobar

a line connecting points of equal pressure

surface map

a map that shows the distribution of sea-level pressure with isobars and weather phenomena

anticyclone

an area of high atmospheric pressure around which the wind blows clockwise in the northern hemisphere and counterclock wise in the southern hemisphere

mid-latitude cyclonic storm

a cyclonic storm that most often forms along a front in middle and high latitudes

isobaric map

a chart showing variables such as temperature and wind, on a constant pressure surface

contour line

a line that connects points of equal elevation above a reference level, most often sea level

ridge

an elongated area of high atmospheric pressure

trough

an elongated area of low atmospheric pressure

pressure gradient

the rate of decrease of pressure per unit of horizontal distance

pressure gradient force

the force due to differences in pressure within the atmosphere that causes air to move and hence the wind to blow

coriolis force

an apparent force observed on any free moving object in a rotating system

geostrophic wind

A theoretical horizontal wind blowing in a straight path, parallel to the isobars or contours, at constant speed

gradient wind

a theoretical wind that blows parallel to curved isobars or contours

centripetal force

the radial force required to keep an object moving in a circular path. It is directed toward the center of that path

meridional wind flow

a type of atmospheric circulation pattern in which the north-south component of the wind is pronounced

zonal wind flow

a wind that has a predominate west to east component

friction layer

the atmospheric layer near the surface usually extending up to about 1 km where the wind is influenced by friction of the earth's surface and objects on it

hydrostatic equilibrium

the state of the atmosphere when there i a balance between the vertical pressure gradient force and the downward pull of gravity

onshore wind

a breeze that blows from the water onto the land

offshore wind

a breeze that blows from the land out over the water

prevailing wind

the wind direction most frequently observed during a given period

wind rose

a diagram that shows the percent of time that the wind blows from different directions at a given location over a given time

wind vane

an instrument used to indicate wind direction

anemometer

an instrument designed to measure wind speed

aerovane

a wind instrument that indicates or records both wind speed and wind direction

wind profiler

A doppler radar capable of measuring the turbulent eddies that move with the wind

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