Chapter 19

© Air pressure weight of air above © Exerted in all directions (up, down, and sideways)

 Unit: called the millibar  Barometer: device used for measuring air pressure

© Types of barometers © Mercury © When air pressure increases, the mercury in the tube rises © When air pressure decreases, the mercury in the tube goes down © Aneroid © recording mechanism providing a continuous record of pressure change over time

 The result of horizontal differences in air pressure  Air flows from areas of high to low.  The unequal heating of Earth’s surface generates pressure differences.  Solar energy is the ultimate energy source for most wind.

 Pressure Differences  Coriolis Effect  Friction

 Wind is created from differences in pressure.  The greater the difference the greater the wind speed.  Shown using isobars:  Lines on a map that connect places of equal air pressure  Closely spaced isobars indicate high winds.

 Closely spaced isobars: indicate a steep pressure gradient and high winds.  Widely spaced isobars: indicate a weak pressure gradient and light winds.

 The Coriolis effect describes how Earth’s rotation affects moving objects.  Northern Hemisphere  Deflected to right  Southern Hemisphere  Deflected to the left  Strongest at the poles, weakest at the equator Coriolis video

© Important only within a few km of Earth’s surface © Slows air movement, which changes wind direction

© Jet streams: fast- moving rivers of air © Travel between 120 and 240 kilometers per hour

CyclonesAnticyclones Centers ofLow PressureHigh Pressure Wind BehaviorWinds blow inward and counterclockwise Winds blow outward and clockwise Weather Associated Severe and stormyFair and Sunny Symbol“L” that is RED“H” that is BLUE

 Underlying cause of wind is the unequal heating of Earth’s surface  Atmosphere balances these differences by acting as a giant heat- transferring system  Warm air towards the poles  Cool air toward equator

 Trade winds  Blow constantly from east  Westerlies  Middle latitudes  Blow from the west  Polar Easterlies  Not constant  Blow east to west  Polar Front:  Interaction of war and cool air masses produces a stormy belt

Four Pressure Zones  Highs: Subtropical and Polar  Dry subsiding air  Prevailing winds  Lows: Equatorial and Subpolar  Inward and upward air  Clouds and precipitation

 Only true continuous pressure belt is the subpolar low.  Uninterrupted by landmasses  Can produce seasonal temperature differences  Monsoons  Seasonal changes in wind direction  Summers: rainy  Winters: dry

 Caused by topographic effects or variations in surface composition  Types of Local Winds  Land Breezes  Sea Breezes  Valley Breezes  Mountain Breezes

 Sea Breezes  Day  Land heated more intensely  So air above the land: heats, expands, and rises  Cool air over water moves toward land. Land Breezes Night Land cools more quickly. Cooler Air over land moves to the sea

V alley Day Land is heated more intensely Air moves up along the slop Mountain Night Rapidly cooling air along the slopes Moves downward

 Direction  Always labeled by the direction from which they blow  Prevailing Wind: wind consistently blows from one direction.

 Anemometer  Measures how fast wind is blowing

El Ni ñ o  Episodes of ocean warming that affect the eastern tropical Pacific.  Warm countercurrents replace normally cold offshore waters.