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What is Air Pressure?

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air pressure
the air exerted by the weight of air above
all directions
in which direction is air pressure exerted?
exactly balances it
What does the air pressure pushing down on an object do to the air pressure pushing up on the object?
barometer
the instrument the measures atmospheric pressure
millibar
the unit scientists use to measure atmospheric pressure
1013.2 millibars
standard sea-level pressure
aneroid barometer
uses a metal chamber with some air removed
variations in air pressure
what is an aneroid barometer extremely sensitive to?
wind
the result of horizontal differences in air pressure
unequal heating of Earth's surface
what generates pressure differences that generate winds?
solar radiation
what is the ultimate energy source for most wind?
pressure gradient
The difference in atmospheric pressure between areas of higher pressure and lower pressure.
isobars
lines of equal pressure on a weather map
a steep pressure gradient and high winds
what do closely spaced isobars indicate?
a weak pressure gradient and light winds
what do widely spaced isobars indicate?
anticyclones
air moves clockwise away from the center
highs/anticyclones
pressure increases from the outside toward the center
lows/cyclones
pressure decreases from the outer isobars toward the center
cyclones
air moves counterclockwise toward the center
cloud formation and precipitation
what is rising air associated with?
low
in what type of pressure areas does the air rise?
clear skies
what does sinking air produce?
high
in what type of pressure area is the air sinking?
Polar Easterlies, Westerlies, and Trade Winds
the atmosphere is divided into these 3 main wind belts
heating from the sun
what causes air at the equator to rise?
the warm air that rose at the equator cools as it moves north and south and descends at 30 degrees. as it descends it warms and dries out
Why do desserts tend to be located at 30 degrees North and South?
at the equator, calm winds
where are the Doldrums located?
trade winds
two belts that blow almost constantly from easterly directions at 30 degrees north and south to the equator. early sailing ships used these winds to sail by
sea breeze
starts developing shortly before noon and generally reaches its greatest intensity during mid- to late afternoon
sea breeze
these relatively cool winds can be a moderating influence on afternoon temperatures in coastal areas
land breeze
the opposite of a sea breeze. they influence the evening temperatures in coastal areas
land breeze
the cooler air over the land moves to the sea, where the air is warmer and at lower pressures
valley breeze
this is created because warmer air on mountain slopes is less dense and it rises up along the slope
mountain breeze
air along the mountain slopes cools and air moves down slope into the valley. air in the valley is still warmer and rises and is replaced by the cooler air