Chapter 7: Chapter 7: Atmospheric Atmospheric circulationscirculations

Scales of atmospheric motionsScales of atmospheric motions Eddies - big and smallEddies - big and small Local wind systemsLocal wind systems Global windsGlobal winds Global wind patterns and the oceansGlobal wind patterns and the oceans

Scales of Scales of atmospheric atmospheric

motionsmotions

Scales of atmospheric Scales of atmospheric motionsmotions

scales of motionscales of motion microscalemicroscale synoptic scalesynoptic scale planetary scaleplanetary scale

• Lots of important weather events occur on microscales, likeLots of important weather events occur on microscales, likeevaporation of liquid water molecules from the earth’s surfaceevaporation of liquid water molecules from the earth’s surface

Eddies - big and Eddies - big and smallsmall

Eddies - big and smallEddies - big and small

eddyeddy rotorrotor wind shearwind shear turbulenceturbulence

• wind shear can sometimes be observed by watching thewind shear can sometimes be observed by watching themovement of clouds at different altitudesmovement of clouds at different altitudes

Local wind Local wind systemssystems

Thermal circulationsThermal circulations

isobars and density differencesisobars and density differences thermal circulationsthermal circulations

Sea and land breezesSea and land breezes

sea breezesea breeze land breezeland breeze sea breeze frontsea breeze front Florida sea breezesFlorida sea breezes

• Sea and land breezes also occur near the shores of largeSea and land breezes also occur near the shores of largelakes, such as the Great Lakeslakes, such as the Great Lakes

Seasonally changing Seasonally changing winds - the monsoonwinds - the monsoon

Monsoon wind systemMonsoon wind system Asian monsoonAsian monsoon other monsoonsother monsoons

Mountain and valley Mountain and valley breezesbreezes

valley breezevalley breeze mountain breezemountain breeze

• The nighttime mountain breeze is sometimes calledThe nighttime mountain breeze is sometimes calledgravity winds or drainage winds, because gravitygravity winds or drainage winds, because gravitycauses the cold air to ‘drain’ downhillcauses the cold air to ‘drain’ downhill

Katabatic windsKatabatic winds

drainage windsdrainage winds borabora

• Katabatic winds are quite fierce in parts of Antarctica, withKatabatic winds are quite fierce in parts of Antarctica, withhurricane-force wind speeds. hurricane-force wind speeds.

Chinook (Foehn) windsChinook (Foehn) winds

Chinook windsChinook winds compressional heatingcompressional heating chinook wall cloudchinook wall cloud

• In Boulder, Colorado, along the eastern flank of the In Boulder, Colorado, along the eastern flank of the Rocky Mountains, chinook winds are so common thatRocky Mountains, chinook winds are so common thatmany houses have sliding wooden shutters to protectmany houses have sliding wooden shutters to protecttheir windows from windblown debris.their windows from windblown debris.

Santa Ana windsSanta Ana winds

Santa Ana windSanta Ana wind compressional heatingcompressional heating wildfireswildfires

• Many Southern California residents regularly hose downMany Southern California residents regularly hose downtheir roofs to prevent fires during Santa Ana wind seasontheir roofs to prevent fires during Santa Ana wind season

Desert windsDesert winds

dust stormsdust storms dust devilsdust devils

Global windsGlobal winds

General circulation of General circulation of the atmospherethe atmosphere

cause: unequal heating of the earth’s cause: unequal heating of the earth’s surfacesurface

effect: atmospheric heat transporteffect: atmospheric heat transport

• Ocean currents also transport heat from the equator toOcean currents also transport heat from the equator tothe poles and back.the poles and back.

Single-cell modelSingle-cell model

basic assumptionsbasic assumptions Hadley cellHadley cell why the single-cell model is wrongwhy the single-cell model is wrong

• One of the world’s premier atmospheric science research facilities,One of the world’s premier atmospheric science research facilities,the Hadley Centre for Climate Research, is named after George Hadleythe Hadley Centre for Climate Research, is named after George Hadley

Three-cell modelThree-cell model model for a rotating earthmodel for a rotating earth Hadley cellHadley cell doldrumsdoldrums subtropical highssubtropical highs trade windstrade winds intertropical convergence intertropical convergence

zonezone westerlieswesterlies polar frontpolar front polar easterliespolar easterlies

• many global circulation terms,many global circulation terms,including ‘trade winds’ and including ‘trade winds’ and ‘doldrums’, were named by ‘doldrums’, were named by mariners who were well acquaintedmariners who were well acquaintedwith wind patternswith wind patterns

Average surface winds Average surface winds and pressure: the real and pressure: the real

worldworld semipermanent highs and lowssemipermanent highs and lows Bermuda high & Pacific highBermuda high & Pacific high Icelandic low & Aleutian lowIcelandic low & Aleutian low Siberian highSiberian high

• The Bermuda High frequently brings hot, muggy weatherThe Bermuda High frequently brings hot, muggy weatherto the eastern USto the eastern US

The general circulation The general circulation and precipitation and precipitation

patternspatterns major controlsmajor controls ITCZ, midlatitude storms, polar frontITCZ, midlatitude storms, polar front

• Most of the world’s thunderstorms are found along the ITCZMost of the world’s thunderstorms are found along the ITCZ

Westerly winds and the Westerly winds and the jet streamjet stream

jet streamsjet streams subtropical jet streamsubtropical jet stream polar front jet streampolar front jet stream

Global wind Global wind patterns and the patterns and the

oceansoceans

Winds and upwellingWinds and upwelling

upwellingupwelling wind flow parallel to the coastlinewind flow parallel to the coastline

• upwelling frequently occurs along the coastupwelling frequently occurs along the coastof Californiaof California

El Niño and the southern El Niño and the southern oscillationoscillation

El Niño eventsEl Niño events Southern OscillationSouthern Oscillation La NiñaLa Niña teleconnectionsteleconnections

• ENSO is an example of a global-scale weather phenomenonENSO is an example of a global-scale weather phenomenon

Other atmosphere-ocean Other atmosphere-ocean interactionsinteractions

North Atlantic OscillationNorth Atlantic Oscillation Arctic OscillationArctic Oscillation Pacific Decadal OscillationPacific Decadal Oscillation

• Other atmosphere-ocean interactions may very well beOther atmosphere-ocean interactions may very well bediscovered in the coming yearsdiscovered in the coming years