Ocean Circulation

1. Ocean Circulation

2. Objectives Demonstrate an understanding of: • Ocean circulation • Coreolis effect • Global wind patterns • Great ocean conveyor

3. Firing a missile • Fig 3.16 • Aim the missile at Charleston --> 2 1/2 hours later it hits San Diego. Why? • Coriolis clip (about halfway) • Landing a jet (Explore--Coriolis Effect)

4. The earth spins! • Causes objects to follow a curved path. What’s this called? • Coriolis Effect: • Deflects large-scale motions (winds/currents) to the right in the northern hemi and to the left in the southern hemi • Show with globe • Demo: spinning paper/record on board • Why don’t we notice it when we are walking or driving? • Detailed explanation • How does this affect the wind patterns? • Let’s look at how convection works first . . .

5. Convection Demo • Convection-wind demo • What is convection? After seeing this demo, converse with your neighbor and come up with a definition and explanation of what’s going on • movement of heat in a fluid (air is a fluid) caused by differences in temp/density • What does this have to do with wind?

6. Wind Patterns • Flashlight/earth demo--what’s happening? • Sun heats the surface of the earth at the equator • What happens to the warm air? • Warm air rises • Cooler, denser air blows in to replace it • Area of low pressure and not much wind • Doldrums • Why not much wind? This doesn’t just happen at the equator . . .

7. The Doldrums • Area of low pressure where the trade winds meet along the equator • Calm, light winds • Warm air rises steadily • Cool air moves in and warms rapidly before it moves too far  no wind

8. Wind Patterns • What happens to the warm, rising air after it releases it’s moisture? • It becomes dry and cold and descends towards earth N & S of equator. • Where does this happen (in terms of latitude)? • 30° N and S. • What type of environment do we usually see here?

9. Global Vegitation. Where are the deserts located?

12. Horse Latitudes • 30° N and S are also called the Horse Latitudes • Winds are variable --> trade winds and westerlies are moving apart • Sailors, after being “stuck” for days, and short of drinking water and food, used to throw dying horses overboard -- it also lightened the load --> easier to sail

13. Wind Patterns • What do you notice at the 60° parallel? • Rising warm, moist air • At the 90 °? • Descending, cool, dry air • What types of pressure zones exist at each of these parallels? • Is there a relationship between these pressure zones and whether the air sinks or rises?

14. Low vs. High Pressure • What’s the relationship? • Low pressure: • Hot, moist, rising air • Clouds and rain • High Pressure: • Cool, dry, sinking air • Sunny • Notice the flow from high to low pressure---This is convection!!! • Explanation (Fig. 7o-3)

15. Wind Patterns • There are six cells • Which directions does the wind flow in each cell? • Always from high to low pressure! • Why doesn’t the air/wind flow in straight lines? • Because the earth spins causing the Coriolis effect Flying a plane? Play merrry-go-round clip

16. Nike and Currents? • Let’s do an activity • hand out current maps • Keep the maps, you will be quizzed on the major currents • Read introduction

17. Wind and Currents • What does the wind have to do with the currents? • Do you see a relationship between wind and major surface currents? • Check with a neighbor and discuss it

18. Wind and Currents • Wind pushes the water • Water moves at 45° angle due to Coriolis effect. • Top layer of water pushes on layer below it • Coriolis effect causes this second layer to move slightly to right and slower. • And so on, and so on until?

19. Ekman Spiral • The water is moving in an opposite direction and eventually no current at all! • Ekman Spiral: • The spiral change of movement of water in the water column • What do you notice about the net movement of water?

20. Ekman Transport • Ekman transport: • The net movement of ocean water at right angles caused by the wind • Is this diagram of the northern or southern hemisphere? • Northern. What direction would the net transport of water be if this was the southern hemi?

21. Currents and Winds With your knowledge of the Ekman transport, explain why the currents flow in the direction they do. (Hint: what do you notice about the wind direction?) Can you identify the trade winds and the westerlies? Chat with a neighbor.

22. Gyres • Currents combine into huge gyres: • Large circular systems of surface currents • remember---you will be quizzed on these currents!!! • Adopt a Drifter program website ---- let's look at some drifting buoys

23. Thermostat? • Giant thermostat -- why? • Bringing cold water to the tropics and warm water to the poles • Regulates climate • Remember though--- these are average patterns over a large distance over a ling time---currents shift with the season, bottom contour, coastline and tides--also, these are surface currents.

24. The ocean is layered • 3 main layers: • Surface/mixed layer • Intermediate layer • Deep layer • What do you notice? • (a) Salinity varies--precipitation, evaporation, river runoff • (a) Temp and density are mirror images--temp controls density • (b) Surface temp varies with latitude--deep water temp much more uniform • (c) Seasonal thermoclines

25. The Great Ocean Conveyor • Where does it “begin?” • Unequal distribution of solar radiation---equator heats up • Water moves as current from tropics towards higher latitudes • i.e., the Gulf stream • cools, transfers heat to atmosphere --> N.W. Europe is warmer than other regions at same latitude

26. The Great Ocean Conveyor • Water moving northward cools • What happens to cooler water • It is denser and it sinks • What else makes water more dense? • Salinity. Why would salinity in the water increase at the poles? • As ice forms, salt ions are left behind

27. The Great Ocean Conveyor • As the colder, saltier water sinks, warm water takes it place, and then too begins to cool • This sinking cold water is called the North Atlantic Deep Water (NADW)

28. The Great Ocean Conveyor • NADW joins the Antarctic bottom water then splits • Circles Antarctica, heads south of OZ • Up east coast of Africa, warms, rises (causes monsoons), and then begins the 1000 year journey all over again.

29. 10 minute animation on currents • Ocean Currents animation

30. The Day After Tomorrow? • The conveyor has a major effect on global climates • Who saw this movie? What caused the freeze? • Global warming --> more freshwater runoff --> less salty, dense water sinking --> slows down conveyor

31. Local Currents: Longshore • Longshore current: • Currents of water flowing parallel to the shore • Waves break, water piles up during a set and travels along shore

32. Longshores at OB Sloat, 2003

34. Rip Current • Rip current: • Fast moving belt of water traveling offshore • Breaking waves over bars --> increase of water level near shore • Converging of longshore currents • Water rushes back out through break in bar • What if you get stuck in one?

35. Swim parallel to shore!