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The Ocean-Atmosphere Connection, Winds & Surface Currents Geosc040, Lecture 9 Feb 11, 2014 Gimme some Water See web for Extra Credit Opportunities See web for Extra Credit Opportunities Thanks to Adam C. Somewhere Beyond The Sea Frank Sinatra Thanks to Steve P. Ocean Avenue Yellowcard Thanks to Adam R.

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Thanks to Kim S. and Bronte A. On-line Assignment (OLA) 4 due today, OLA 5 due Thursday OLA 4 = OLA 5, Make sure to get 100% on 5. You have two attempts. Highest score counts OLA 6 due on Feb 18 th Homework 2 will be posted tomorrow Read Chapter 7

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Quiz 1 Mean was 79.4. It is now 83.4. I added 4 points to everyones score. Your score on Angel includes the bonus points. I add extra credit points, for cell phone recycling, to quiz 1 at the end. Ill add in the extra credit any time I use quiz 1, when I calculate your final exam grade, if you decide not to take the final when I calculate the final grade

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The Ocean-Atmosphere Connection, Winds & Surface Currents EARTHs ORBIT (elliptical) In 4 easy pieces: Heating, Wind, Currents, Coriolis,

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EARTHs ORBIT (elliptical) SEASONALITY Effects of Earths Axial Tilt Northern Hemisphere summer (solstice) occurs when tilt is toward the sun. Systematic variation in solar energy receipt on a yearly basis is produced by Earth s axial tilt and orbit around the sun. The Earth is closest to the sun in January

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Seasonal variations, but the equatorial regions receive more heat YEAR IN and YEAR OUT!

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GLOBAL ATMOSPHERIC CIRCULATION (WINDS) Temperature gradients create pressure differences which drive winds

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GLOBAL ATMOSPHERIC WINDS, PLUS THERMOHALINE CIRCULATION, DRIVE OCEAN SURFACE CURRENTS

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Gulf Stream as an example of a Western Boundary Current

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In 4 easy pieces: Heating, Wind, Currents, Coriolis, The Ocean-Atmosphere Connection, Winds & Surface Currents

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Some Strange Doings In order to comprehend the pattern of surface circulation produced by the global wind systems (responding to pressure differences), we need to introduce: The Coriolis Effect (Coriolis Force)

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Gustav Why do winds circulate in an organized pattern around High and Low pressure systems? In the N. Hemisphere winds circulate: Counterclockwise around low pressure Clockwise around high pressure

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Coriolis Considerations angular rotation rate is same but velocity changes with circumference as a function of latitude

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Coriolis Considerations Quito travels a greater distance during a day than does Buffalo What happens if you move something (wind!) from Quito to Buffalo? Think about inertia!

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Coriolis Considerations Think about inertia!

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Coriolis Considerations Coriolis Effect ( Force ) moves things to the right in the Northern hemisphere and to the left in the Southern hemisphere Angular Momentum and Inertia of wind and water currents mean that they do not travel in a straight line on Earth

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North Atlantic Gyre Effect of winds and coriolis Download this file to see the video: http://www.youtube.com/ watch?v=_36MiCUS1ro

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North Atlantic Gyre Effect of winds and coriolis Download this file to see the video: http://www. youtube.co m/watch?v =_36MiCU S1ro

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Coriolis Considerations angular rotation rate is same but velocity changes with circumference, which varies with latitude Coriolis effect arises from conservation of momentum (angular momentum)

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Coriolis Considerations In the northern hemisphere: Coriolis Effect ( Force ) moves things to the right of their initial trajectory

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Coriolis Considerations In the northern hemisphere: Coriolis Effect ( Force ) moves things to the RIGHT of their initial trajectory

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Coriolis Considerations In the Southern hemisphere Coriolis Effect moves things to the LEFT OF THEIR INITIAL TRAJECTORY

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North Atlantic Gyre Effect of winds and coriolis

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Credit: NASA In the northern hemisphere: Coriolis Effect ( Force ) moves things to the right of their initial trajectory In the Southern hemisphere Coriolis Effect moves things to the LEFT OF THEIR INITIAL TRAJECTORY

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The Coriolis effect causes objects in motion to veer off their initial trajectories. Which of the following is/are true: A.Objects are deflected to the right in the northern hemisphere B.Objects are deflected to the left in the northern hemisphere C.Winds blowing from south to north in the northern hemisphere are deflected to the east. D.Winds blowing from south to north in the northern hemisphere are deflected to the west. E.A and C

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The Coriolis effect. Which of the following are true: A.Winds blowing to the south in the Southern hemisphere are deflected to the east. B.Winds blowing to the north in the Southern hemisphere are deflected to the west. C.Winds blowing to the north in the Southern hemisphere just go straight D.A and B E.None of the above

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Which statement(s) is/are true about global wind patterns? A) Low pressure develops at 30 N and 30 S B) Easterly winds between the Equator and 30 N are caused by surface winds that blow south and are deflected by the Coriolis effect C) High pressure develops over the equator because of rising air D) Winds blow directly from the equator to the poles along the surface in one large convection cell E) All of the above

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Strange Doings Coriolis acceleration a c where is the angular velocity (magnitude equal to the rotation rate ) and v is the velocity of the object in the rotating systemangular velocity The Coriolis acceleration may be multiplied by the mass of the relevant object to produce the Coriolis force: F c = m a c See: http://en.wikipedia.org/wiki/Coriolis_effect

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North Atlantic Gyre Effect of winds and coriolis Variation of Coriolis with latitude causes differences between Eastern and Western Boundary Currents

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Lets look at the Gulf Stream as an example of a Western Boundary Current formed in this way WBC EBC

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Gyres and Sea-surface Topography The Hill is a balance between Coriolis and Pressure

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Sea-Surface Height Differences Differences of up to 1 meter maintained by wind Notice the pileup of water in Western Pacific warm pool Also note the pileup around Bermuda in the N. Atlantic gyre

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More Strange Doings In order to comprehend the pattern of surface circulation produced by the global wind systems (responding to pressure differences), we need to introduce another issue: The Ekman Spiral

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Wind Wind moves surface water (friction) Velocity of water decreases with depth because of friction between water molecules Let s now examine how winds drive surface ocean circulation Surface

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Effects of friction on Surface Currents In the northern hemisphere water at the sea surface moves to the right of the wind direction

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Wind currents drive ocean surface currents Energy from wind transferred to water by friction Then, due to the Coriolis Effect: Overall, the Oceans surface waters (recall pycnocline and deep water) move, on average, 90 o to the wind direction

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0 30 60 Consider a hypothetical ocean with straight coastlines In the southern hemisphere water at the sea surface moves to the left of the wind direction How do global wind patterns influence ocean surface currents?

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0 30 60 Consider a hypothetical ocean with straight coastlines Blue arrows show local wind direction at the sea surface Now, think about local current direction of ocean surface water (yellow arrows)

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Ocean currents form large GYRES 0 30 60 These are a product of wind direction, the Coriolis effect, and Ekman spiral effects.

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Wind-driven circulation Western Boundary Currents Gulf Stream, Kuroshio, Labrador, Kamchatka (Oyashio) Eastern Boundary Currents Canary, California Ocean Surface Currents How does this work?

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In Earth s southern hemisphere: a) western boundary currents in the ocean bring warm water southward. b) winds rotate clockwise around low pressure systems c) winds only blow from north to south. d) circulation in large scale oceanic gyres is clockwise e) (a) and (b)

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The Coriolis effect causes objects in motion to veer off their initial trajectories. Which of the following are true: A. Objects are deflected to the left in the southern hemisphere B. Objects are deflected to the right in the northern hemisphere C. Winds blowing from south to north in the northern hemisphere are deflected to the east. D. Winds blowing from south to north in the southern hemisphere are deflected to the west. E. All of the above

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Which of the following are true: A. Winds blowing to the south in the Southern hemisphere are deflected to the east. B. Large scale Gyres in the ocean are surface currents that are not affected by the Coriolis effect C. Western boundary currents are fast and narrow because of variations in the Coriolis effect with latitude D. The Coriolis effect causes water to pile up in the center of gyres E. All but B.

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Example: The Gulf Stream Note these features: Sharp boundaries of currents (1 & 2) Eddies Warm-core rings (3) Cold-core rings (4) Labrador Current Gulf Stream This is a map of surface water temperature Surface currents transport heat toward poles

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Gulf Stream Heat Transfer: Is that all there is to it? OK, warm water flows toward the poles, but How does heat actually get transferred?? Two mechanisms: 1) Sensible heat transfer to atmosphere 2) Latent heat transfer (remember: evaporation- precipitation?)