Surface Currents Origin of Currents Ocean surface currents are wind driven Ocean surface currents are wind driven Air movement due to less dense air rising and more dense air sinkingAir movement due to less dense air rising and more dense air sinking Horizontal air flow along Earths surface is windHorizontal air flow along Earths surface is wind Air circulating in this manner is convection currentsAir circulating in this manner is convection currents Convection Currents Air becomes less dense when: Air becomes less dense when: It is warmed Atmospheric pressure Water vapor (humidity) Air becomes more dense when:Air becomes more dense when: It is cooled Atmospheric pressure Water vapor (dry air) Warm and Cold Fronts Caused by eastward moving air massesCaused by eastward moving air masses Warm air rises over cold, dense air condenses and precipitates Steeper cold front pushes warm air up cools, condenses and precipitates Wind Movement Non-rotating Earth Simple wind pattern Simple wind pattern Warm air rises at equator, flows toward poles Air cools at poles, sinks, and flows toward equator Winds named by direction from which they blowWinds named by direction from which they blow North-blowing winds = southerly winds South-blowing winds = northerly winds Wind Movement Rotating Earth At equator, warm air risesAt equator, warm air rises Zone of low pressure Clouds and precipitation Reaches troposphere and moves poleward As it spreads, it cools 30 N&S, cool air sinks30 N&S, cool air sinks Area of high pressure Dry conditions Location of world deserts 60 N&S, air masses meet60 N&S, air masses meet Form Polar Front Air masses rise, diverge and 90 and 30 N&S Wind Movement Air that sinks does not flow back in a straight north-south path it curves (Coriolis Effect)Air that sinks does not flow back in a straight north-south path it curves (Coriolis Effect) At equator, warm air rises, condenses and precipitatesAt equator, warm air rises, condenses and precipitates At 30 and 90, cool air sinksAt 30 and 90, cool air sinks Rotation on a Globe Speed of Rotation Apparent Deflection Wind Movement Coriolis Effect Deflected winds due to movement over spinning object Deflected winds due to movement over spinning object In Northern Hemisphere:In Northern Hemisphere: In Southern Hemisphere:In Southern Hemisphere: Winds are deflected to the right Travel clockwise around high P Winds are deflected to the left Travel counter-clockwise around high P Produce wind bands Assume water-covered Earth High and Low Pressure CyclonesCyclones AnticyclonesAnticyclones Low pressure air Converge Ascend High pressure air Diverge Descend In Northern Hemisphere High and Low Pressure Areas Land masses modify wind bandsLand masses modify wind bands Variations in Wind Daily Coastal Areas DaytimeDaytime Warmer land; cooler sea Onshore flow EveningEvening Cooler land; warmer sea Offshore flow Variations in Wind Seasonal In summer:In summer: January July Air rises over warmed land, condenses Sudden and large volume of precipitation Winds accumulate more H 2 O vapor from ocean In winter have opposite effectIn winter have opposite effect Surface Current Circulation Ekman Transport Net water movement 90 to right of wind direction in N. Hemi.Net water movement 90 to right of wind direction in N. Hemi. Winds over H 2 O set ocean surface currents in motionWinds over H 2 O set ocean surface currents in motion Surface H 2 O is deflected 45 by Coriolis EffectSurface H 2 O is deflected 45 by Coriolis Effect In Northern Hemisphere Deflection increases with depthDeflection increases with depth Upwelling and Downwelling West Coast of N. AmericaWest Coast of N. America Northerly winds summer upwelling Southerly winds winter downwelling Divergence and Convergence ConvergenceConvergence Wind-driven currents collide Downwelling DivergenceDivergence Currents move away Upwelling Equatorial regionEquatorial region Created by SE and NE trade winds Divergence Upwelling Warm and Cold Currents Uneven solar heating produces ocean temperature patternUneven solar heating produces ocean temperature pattern Clockwise rotation in Northern HemisphereClockwise rotation in Northern Hemisphere Ocean currents redistribute heat and influence climateOcean currents redistribute heat and influence climate Surface Currents and Coriolis Effect Moving water deflected by Coriolis EffectMoving water deflected by Coriolis Effect Wind deflection creates ocean circulation gyresWind deflection creates ocean circulation gyres Ocean currents are driven by windOcean currents are driven by wind Water piles up, gravity causes H 2 O to flow down slopeWater piles up, gravity causes H 2 O to flow down slope Geostrophic Currents Gyres Convergence thickens surface layer builds a domeConvergence thickens surface layer builds a dome Circular current systems in major ocean basins: GyresCircular current systems in major ocean basins: Gyres gyre Boundary currents parallel to ocean marginsBoundary currents parallel to ocean margins Pacific Currents Equatorial and boundary currents ConvergenceEquatorial and boundary currents Convergence Warm currents in West Pacific Cold currents in East Pacific i.e. Kuroshio, Australia i.e. California, Peru Western Intensification Gyres displaced to west by Earths rotationGyres displaced to west by Earths rotation Western IntensificationWestern Intensification Faster, narrower currents Eastern CurrentsEastern Currents Slower, more diffuse currents El Nio Year Factors producing El Nio yearFactors producing El Nio year Warmer H 2 O moves east Rainfall shifts from eastern to western Pacific May result from atmospheric pressure changesMay result from atmospheric pressure changes Thermocline deepens Trade winds weaken Upwelling ceases along western S. America El Nio Impact Leads to death of cold-water organismsLeads to death of cold-water organisms Warm-water organisms migrate north and southWarm-water organisms migrate north and south