Global air circulation

This topic focuses on Geography Grade 11 content on Global Air Circulation.

1. GLOBAL AIR CIRCULATION
Presentedby:MrTMokgopa
:[email protected]

2. GLOBAL WIND AND PRESSURE BELTS AS A RESPONSE TO
THE UNEQUAL HEATING OF THE ATMOSPHERE
•EquatorialRegionsreceivemoreinsolation
thanPolarRegions.
•Land/Earthheatsupandcoolsinacycleof
aday.
•ThemechanismthatsetsuptheEarth’s
generalcirculationpatternisthe
Latitudinalheattransfer.

3. AIR PRESSURE AND THE RELATIONSHIP BETWEEN
AIR PRESSURE AND TEMPERATURE
•Air pressure is created by molecules that constitute air through their motion, side, and number.
•Pressure and density both decrease with an increase in altitude.
•Relationship between Air Pressure and Temperature:
•Low Pressure System: Warmer Temperatures
•High Pressure System: Colder Temperatures

4. WIND, WIND SPEED, WIND DIRECTION
AND NAMING OF WINDS
•Simplyput,Windreferstothehorizontalmotionofair.
•Averticalcomponentofwindresultsfromturbulences.
•Propertiesofwind:SpeedandDirection.
•Anemometer:Measureswindspeed.
•WindVane:Determineswinddirection.
•WINDSARENAMEDFROMTHEDIRECTIONFROMWHICHTHEYORIGINATE.

5. DRIVING FORCES WITHIN THE
ATMOSPHERE
1.GravitationalForce.
2.PressureGradientForce.
3.CoriolisForce.
4.FrictionForce

6. PRESSURE GRADIENT FORCE
•This force drives air from higher barometric pressure to lower barometric pressure.
•A Gradientis the rate of change in some property over distance.
•Unequal heating of Earth results in the existence of High-pressure and Low-pressure systems.
•When the two varying air masses are near each other, a pressure gradient force develops.
•Vertical air movement can also cause pressure gradient force.
•High-pressure: Subsiding and diverging air.
•Low-pressure: Rising and converging air.

7. CORIOLIS FORCE
•ThisaforcethatdeflectswindonEarth’srotatingsurface.
•IfEarthwasnotrotating,windwouldtravelinastraightpatternastheymovefromareasofhigh-
pressure,toareasoflow-pressure.
•TheCoriolisForcedeflectsanythingflyingacrosstheEarth’ssurface.
•ThestrengthoftheCoriolisForcevariesatdifferentlatitudes.
•ThereisnoCoriolisForceattheEquator.

8. FRICTION FORCE
•TheFrictionalforcedragswindasitmovesacrossthesurfaceoftheEarth.
•Withoutthefrictionalforce,thewindwouldcontinuallyflowathigherspeeds.
•Generally,aswindflowsthroughroughersurfaces,thepresenceoffrictionishigher.

9. PRIMARY PRESSURE AREAS AND ASSOCIATED
WINDS
JANUARY AVERAGE SURFACE BAROMERTIC
PRESSURES
JULY AVERAGE SURFACE BAROMETRIC
PRESURES

10. EQUATORIAL LOW/ ITCZ: Warm and Rainy
•Located at the 0°latitude.
•Receives constant high altitude of the Sun.
•Associated with the Low-pressure system.
•Intertropical convergence zone (ITCZ): Identified by bands of clouds along the equator.
•Associated with TRADE WINDS
•Winds are calm within the ITCZ. REASON? Weak Pressure Gradient.
•These equatorial calm conditions are referred to as Doldrums.

11. SUBTROPICAL HIGHS: Hot and Dry
•Locatedbetween20°and35°latitudesinbothhemispheres.
•Thesesubtropicalanticyclonesgenerallyformasairabovesubtropicsinpusheddownward.
•Sincewarmaircanabsorbwatervapour,thedescendingwarmairisrelativelydry.
•Severalhigh-pressureareasaredominantintheSubtropics.
•BermudaHigh:TheAtlanticsubtropicalhighintheNH.
•IntheSH,threelargehigh-pressurecentresdominatethePacific,Atlantic,andIndianOceans.
•AssociatedwiththeWesterlies.

12. SUBPOLAR LOWS: Cool and Moist
•Twolow-pressurecycloniccellsexistovertheoceansaround60°N.
•AleutianLow&IcelandicLow.
•Thesecellsaredominantinwinter.
•Polarfront:areasofcontrastwheremassesofairwithdifferentcharacteristicsmeet.

13. POLAR HIGHS: Frigid and Dry
•Characterizedbyweakcells.
•ThepolarregionsreceivelittleenergyfromtheSun.
•AssociatedwiththePolarEasterlies.
•CharacterizedbycoldanddrywindsthatmoveawayfromPolarRegionsinananticyclonic
direction.
•TheAntarctichasstrongerandpersistenthigh-pressuresystem,theAntarcticHigh.

14. THE TRI-CELLULAR CIRCULATION WITH WINDS

15. THE END!!!