E&S Science Chapter 19 Notes – Air Pressure and Wind
Name __________________________
Air Pressure - pressure exerted by the weight of air __________

Air pressure is exerted in all _____________ - Down, up, sideways
o Pressure pushing down on an object balances air pressure pushing up on the object!

Average air pressure at ______ level: 1 kg/cm2 or 1 atmosphere

Measuring Air Pressure
o ___________ – a device used for measuring air pressure
 Measured in units called ___________
 Two types

____________ – glass tube, dish of mercury
o when air pressure increases, mercury in tube rises
o when air pressure decreases height of mercury decreases

____________ – partially emptied metal chamber sensitive to variations in air pressure
o Provides continuous record of pressure changes over time
Factors affecting Wind

Wind – result of _______________ differences in air pressure
o Air flows from areas of higher pressure to lower pressure

Unequal ____________ of Earth’s surface generates pressure differences
o Solar radiation is source
o If Earth did not rotate, air would flow in a ____________ line from areas of higher to lower pressure

Three factors combine to control wind:
o Pressure differences, Coriolis effect, friction
Pressure Differences

______________ – lines on a map that connect places of equal pressure

Pressure ______________ – pressure changes indicated by spacing of isobars
o A steep pressure gradient causes greater ____________________ of air
o Closely spaced isobars indicate ___________ pressure gradient and _________ winds
o Widely spaced isobars indicate _________ pressure gradient and _________ winds

____________ gradient is driving force of wind!!!

Direction of force is always from areas of higher to lower pressure and at _________ angles to isobars
Coriolis Effect

Describes how Earth’s rotation affects moving objects

All free-moving objects, including wind, are ______________ to the ________ of their path of motion
in the N.H.
o In the S.H. they are deflected to the left

Northern Hemisphere – ___________________ motion

__________________ Hemisphere – clockwise motion

A rocket launched from North Pole toward a large target on equator
o It will land 15° West of its target
o The Earth would have rotated 15° East under the rocket in one hour

This deflection:
o Always directed at right angles to direction of ______________
o Affects ___________ wind direction, not wind speed
o Is affected by wind speed – ______________ wind, greater deflection
o Strongest at poles and weakens toward _____________ becoming non-existent
Friction

Friction of wind is only important within a few ____________ of Earth’s surface
o _________ air movement – changes wind direction
o When air above friction layer, pressure gradient causes air to move across isobars
o Pressure gradient and Coriolis effect ______________ in high-altitude air and wind flows parallel to
isobars
Pressure Centers and Winds

Centers:
o _________ pressure – lows or cyclones
 Pressure ______________ from outer isobars toward the center
o High pressure – highs or anticyclones
 Values of isobars ______________ from outside toward center

_____________ and Anticyclonic Winds
o When pressure gradient & Coriolis effect applied to pressure centers in _______________
Hemisphere:
 Around a ________ – winds blow counterclockwise
 Around a high – winds blow ______________
o _____________ Hemisphere:
 Around a low – winds blow _____________
 Around a ________ – winds blow counterclockwise
o Both Hemispheres friction causes:
 Cyclone – net flow of air ______________
 Anticyclone – net flow of air _____________
Weather and Air Pressure

Cyclonic flow – horizontal convergence on ____________ (pushes air up)
o Divergence aloft (above air system)
o Related to unstable systems and __________ weather

Anticyclonic flow – horizontal divergence on surface
o _______________ aloft (pushes air down)
o Related to clear skies and ________ weather
Weather Forecasting

Low pressure centers – produce bad weather in any _______________
o __________________ direction across U.S.
o Take a few days, up to more than a week
o Paths can be unpredictable
Global Winds

____________ regions – ___________ solar radiation is received than is radiated back to space

Polar regions – ___________ solar energy is received than lost

Giant Heat Transfer System:
o ________ air moved toward high latitudes
o Cool air moved toward __________

Non-Rotating Earth Model
o Smooth surface
o Heated air at equator would rise until reaching _______________
o Tropopause would deflect hot air towards _________
o Air would reach poles, sink, spread out in all directions and move back towards ______________

Rotating Earth Global Winds
o __________ and tropical cells retain earlier characteristics
 ____________ latitudes are different
o Equatorial low – region characterized by ________________ precipitation
 Produced by rising air
o ____________ N or S latitude of equator
 Hot, arid conditions due to sinking air
 Great deserts of Australia, Arabia, Sahara

__________ winds – two belts of wind that blow almost constantly from ____________ directions
o Located between subtropical highs and equator

___________ – air that travels to the poles and is deflected, generating _____________ wind of middle
latitudes
o Dominant west-to-east motion of atmosphere in regions on _____________ side of subtropical highs

Polar _________________ – winds that blow from polar high toward ________________ low
o Not constant
o Cold polar air sinks and spreads towards ____________

Polar Front – interaction of warm and cool air masses
o Produce a _____________ belt
Circulation in 4 Pressure Zones
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Subtropical and Polar regions – areas of dry sinking air that flows _______________ toward surface
o Produces ____________ winds
o __________ pressure zones

Equatorial and subpolar regions – associated with _____________ and ____________airflow
o Accompanied by clouds and precipitation
o ________ pressure zones
Influence of Continents

Only continuous belt without influence of land is _________ ______ in S.H.

At other latitudes, particularly N.H., seasonal temp changes disrupt pressure pattern

Large land masses:
o become _________ in winter – seasonal ________ pressure system develops (airflow off land)
o _________ in summer – seasonal ________ pressure system develops (airflow onto land)

Monsoons – seasonal changes in wind __________
o Summer - ________
o Winter - _______
Regional Wind Systems

Local Winds – caused by topographic effects or variations in surface composition (________ and
________)
o _______ breezes – cooler air over sea (higher pressure) blows to land (lower pressure)
 Breeze develops before ________ and goes to late afternoon
 Can also develop on shores of lakes
o _______ breeze – cooler air over land (higher pressure) than sea (lower pressure)
 cooler air blows towards the sea
 Happens at ________
o _________ breeze – warmer air on mountain slopes tends to ________
 Daytime
 More dominant in warmer seasons
o ___________ breeze – cooler air on mountain slopes ________ to valley
 Nighttime
 Coldest pockets of air usually found in lowest spots
 More dominant in __________ seasons
How Wind is Measured

__________ – winds labeled direction _________ which they blow
o I.E. – North (north to south)
o Wind vane used to measure
o _____________ wind – when wind blows _____________ from one direction to another


Westerlies consistently move weather from west to east (winds vary)
___________ - measured by an _______________
o Read from dial like a speedometer
El Niño

Cold ___________ current – flows towards ____________ along coasts of Ecuador and Peru
o upwelling of cold nutrient-rich waters
o Near end of year, __________ current replaces cold current & lasts a few weeks

Every _______ yrs, countercurrents unusually strong, replacing cold offshore waters with warm
equatorial waters
o Marked by ____________ weather patterns
o Normally arid inland areas receive lots of ________
o Part of a global circulation
La Niña - When temps in eastern pacific are ___________ than normal

Blows colder than normal air over Pacific Northwest and northern Great Plains
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Warms much of rest of U.S.

Northwest – greater precipitation

Also can increase ___________ activity
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Different effects all over globe
Global Distribution of Precipitation

___________ region on Earth – ___________ region dominated by equatorial ________
o Rainforests of South America and Africa
o Warm, humid trade winds converge

___________ – areas dominated by subtropical _______-pressure cells

___________ of large land masses – decreased precipitation