Robert W. ChristophersonCharlie ThomsenChapter 6Atmospheric and Oceanic CirculationsWinds: Transfer energy and mass(1) Balance energy equatorial energy surplus and polar energy deficit(2) Generate Earth weather pattern(3) Generate ocean currents(4) Dilute air pollutants(5) Supply vegetation with CO2in the air.Wind is a vector varibleTemperature is a scalar variable.Atmospheric and Oceanic CirculationsWind EssentialsDriving Forces within the AtmosphereAtmospheric Patterns of MotionOceanic CurrentsWind EssentialsAir Pressure and Its MeasurementMercury barometerAneroid barometerWind: Description and MeasurementWind Anemometer Wind vaneGlobal WindsBarometersFigure 6.2History: Torricelli, Galileo’s pupil, working on mine-draining problem.Partially emptied chamberAir Pressure ReadingsFigure 6.3Wind Vane and AnemometerFigure 6.4Driving Forces within the AtmospherePressure Gradient ForceCoriolis ForceFriction ForceGravityPressure Gradient ForceFigure 6.7Without pressure gradient force, the air will not move, then there will be no Coriolis force, no friction force.Coriolis ForceFigure 6.9It deflects and anything that flies or flows across Earth surface: wind, airplane, ocean currents etc.Coriolis Force only changes the direction of movement, not the speed. It is always perpendicular to the direction of movement, to the right hand side on Northern Hemisphere. Pressure + Coriolis + FrictionFigure 6.8Pressure Gradient Force onlyPressure Gradient +Coriolis ForcesPressure Gradient+Coriolis+Friction ForcesAtmospheric Patterns of MotionPrimary High-Pressure and Low-Pressure AreasUpper Atmospheric CirculationLocal WindsMonsoonal WindsGeneral Atmospheric CirculationFigure 6.12General Atmospheric CirculationFigure 6.12Primary High-Pressure and Low-Pressure AreasEquatorial low-pressure troughPolar high-pressure cellsSubtropical high-pressure cellsSubpolar low-pressure cellsEquatorial Low-Pressure TroughIntertropical convergence zone (ITCZ)Clouds and rainTrade winds: The trade winds were named during the era of sail ships that carried trade across the seas.Global Barometric PressureFigure 6.10Aleutian LowIcelandic LowAzores HighHawaiian HighGlobal Barometric PressureFigure 6.10Pacific highBermuda highWind Portrait of the Pacific OceanFigure 6.6Wind pattern derived froma radar scatterometer aboardSeasat on a day in September.Note: compare wind pattern and the visible earth below:June–July ITCZFigure 6.11Constant Isobaric SurfaceFigure 6.15Two ways to visualize pressure field:(1) Isobar on Earth surface (isolineof constant air pressure)(2) Constant Isobaric Surface: surface height of constant pressure described by the isolineof constant height (similar to topomaps)Upper Atmospheric CirculationRossby wavesJet stream: a fast flowing narrow air currents in the upper atmosphere (tropopause: the transition between troposphere and stratosphere)Rossby WavesFigure 6.16Jet StreamsFigure 6.17Local WindsLand-sea breezesMountain-valley breezesKatabatic windsLand-Sea BreezesFigure 6.18Mountain-Valley BreezesFigure 6.19Katabatic Wind: A regional scale gravity driven wind, usually needs a high plateau to cool the air, and become dense and flow downslope.Monsoonal WindsFigure 6.20Regional wind systems seasonally changes direction and intensity associated with changes temperature and precipitation. Oceanic CurrentsFunction: Mixing sea waterSurface warm water with deep cold waterCO2 absorptionClimateBiogeochemical processes: phytoplankton growthDriving force: the frictional drag of windsThus we have an Atmosphere-Sea are coupled system. Once the current starts to move, the Coriolis force will kick in. Then there is “friction” between upper and lower water, the shear stress.Major Ocean Surface CurrentsFigure 6.21Surface ocean currents are driven by air circulation around subtropical high pressure cells.Equatorial Currents/Western IntesificaitnCorresponding to trade winds on both sides of the Equator, these winds drives the surface current westward along the equator, called equatorial currents.The equatorial currents push water piles up against the eastern shores of the continent. This is called western intensification. The piled up water will go either up north or down south . The Gulf Stream is one caused by western intensification.Upwelling/Downwelling CurrentsFigure 6.22Upwelling Currents: When surface water is swept away from a coast, an upwelling current occurs. This cool water generally is nutrient rich, e.g. Pacific Coast of North and South AmericaDownwelling Currents: Accumulation of surface water (e.g. western end of equatorial current) can gravitates downward to generate a downwelling current.Deep-Ocean Thermohaline CirculationFigure 6.22Thermahaline Circulation is caused by differences in density as a result of temperature and salinity gradients.Cold and saltier water is heavier, thus tends to sink, forming downwelling currents.Robert W. ChristophersonCharlie ThomsenGeosystems 7eAn Introduction to Physical GeographyEnd of Chapter
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