1General Atmospheric CirculationV1003 - Science and SocietyTake away concepts and ideasThe Earth is heated unevenly.Why there are seasons.Global-scale wind patterns.Geostrophic flow: Balance of forces that act onatmospheric flow (Pressure gradients & gravitybalanced by Coriolis force)Wind belts and climate zones.Monsoonal climate.1. As a sphere, the Earth is unevenly heated,equator to poles2. As a tilted sphere, the Earth has seasonsSeasonal changes in solar energywinter summer wintersummer winter summer The equation of state (air)Atmospheric Pressure is a function oftemperature and densityIdeal Gas Law: P = ρ R Tif pressure is constant, then whathappens to ρ as T increases?2Concept of horizontal motion:Sea BreezePressure imbalance = flow1. Pressure imbalance is a FORCE(F = m x a)2. Law of mass continuity (empty spacesnot tolerated in fluids)Earth’s uneven radiation1. Earth is a sphere (unevenradiation)2. Tilted (there are seasons)Sphere means equator gets moreradiation than poles.Tilt mean the amount of radiation atone location changes with time(seasons).Incoming (and outgoing) radiationHeating imbalance (∆T) =Pressure imbalance (∆P) = WindsQ1: Knowing uneven heating and P = ρ R Ta) Poles have lowpressure, equator hashigh pressure?b) Equator has lowpressure, poles havehigh pressure?3BUT - The Earth rotatesApparent (inertial) forces control the flow of airin response to these pressure gradients.Centripedal force is the forceacting on body by stringCentrifugal force is the oppositeforce acted on by the ball (by itsown inertia)Imagine a satellite in orbitCentripetal force = GravityCentrifugal force = massand acceleration ofsatelliteExact balance sets theangular velocity of thesatelliteThe Coriolis ForceArtifact of Earth’s rotationAn apparent force whichacts on motion on theearth’s surfaceConservation of angularmomentumFcoriolis = 0 on equator,increases polewardCoriolis ForceCons. of Angular MomentumGeostrophic Balance… the pressure gradient force (∆P) is balancedby Coriolis force.Applies to atmosphere and ocean circulationwhere friction can be ignored.Geostrophic balanceBalance between pressure and coriolis forces4Geostrophic BalanceNORTHERN HEMISPHEREGeostrophic flow in theNorthern HemisphereCounter-clockwise around low pressure cellsClockwise around high pressure cellsOpposite Coriolis deflection foropposite hemispheresAn example of Geostrophic flowLowHighQ2: What direction is the wind comingFROM in Burlington, VT today?A) NorthB) EastC) WestD) SouthBurlingtonApplication to EarthGeostrophic flow gives rise to banded circulation zones5Trade Winds and theIntertropical Convergence Zone (ITCZ)ITCZHadley CellTropical convection cellsTradewindsHadley CellwesterliesTradewindsGlobal vegetation patternsRising limb of Hadley Cell(ITCZ) = RainforestDescending limb of HadleyCell = DesertsGlobal VegetationIncoming (and outgoing)