1. Wind and Ocean Circulation

2. Why Are Air and Ocean Currents Important?
Oceans are important to the earth’s climate
They redistribute heat around the globe
They absorb heat, helping to regulate the earth’s temperature
Air and Ocean currents work hand-in-hand

3. Ocean Currents are influenced by two types of forces
1. Primary Forces--start the water moving The primary forces are: 1. Solar Heating- cause water to expand 2. Winds- blows on surface, push water 3. Gravity- pull water down “hill” 4. Coriolis- intervenes and causes water to move to the right, around mound of water 2. Secondary Forces--influence where the currents flow 1. Surface Circulation: tied to the prevailing wind circulation of the atmosphere; general pattern of these surface currents is a nearly closed system of currents, called gyres

4. Winds Unequal heating by the sun causes differences in air pressures.
Cold air drops while warm air rises.

5. Warm air expands = low pressure because it is spread out and less dense
Cold air sinks = high pressure because it is compact and more dense

6. Winds and Coriolis Effect
This causes a circulation of air to occur in a north-to-south direction
However, the Coriolis effect deflects these winds, so wind patterns are a bit more complicated

7. What is the Coriolis Effect?
On the earth, the effect tends to deflect moving objects to the right in the northern hemisphere and to the left in the southern and is important in the formation of cyclonic weather systems
The curvature of things moving across the earth as it rotates
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8. Atmospheric Cell Loops
There are 3 atmospheric cell loops that exist:
Hadley Cells
Warm air rises near the equator, cools, falls in the subtropics, then goes back to the equator
Ferrel Cells
Air rises in sub-polar regions, cools and falls in the sub-tropics, then moves toward the poles
Polar Cells
Air descends at the poles and moves toward the equator

9. What are Prevailing Winds
What are Prevailing Winds? Prevailing Winds are winds that affect large areas, therefore affecting weather around the whole world. • Due to the Earth rotating, the direction of prevailing winds form a unique pattern.
Three main prevailing winds:
Trade winds – blow surface water westward
Westerly winds – blow surface water back towards the east
Polar winds- the dry, cold prevailing winds that blow from the high-pressure areas of the polar highs at the north and south poles towards low-pressure areas within the Westerlies at high latitudes

10. Prevailing Winds Latitude/Wind Direction
Polar Easterlies Between 60° latitude and the poles; From East to West
Mid-latitude
Westerlies Between 30° and 60° latitude; From West to East
Northeast Trade
Winds Near 0°, North of the Equator to °N; From Northeast to West
Southeast Trade
Winds Near 0°, South of the Equator to 30° ;From Southeast to West

11. The Coriolis Effect on Prevailing Winds
As the Earth rotates, the path of prevailing winds is deflected.
Since the Earth rotates to the East . . .
In the Northern hemisphere, the Earth is rotating counterclockwise, so the prevailing wind is deflected to the right.
In the Southern hemisphere, the Earth is rotating clockwise, so the prevailing wind is deflected to the left.

12. Surface Currents (Surface Circulation)
These waters make up about 10% of all the water in the ocean.
Are the upper 400 meters of the ocean.
Important to climate of the earth
Transport heat energy from tropics to cooler parts of the globe
Impact shipping and fishing industries as well

13. Cyclones and Anticyclones
Anticyclones occur where cooler air sinks and a zone of high atmospheric pressure develops
These form at subtropical latitudes
Cyclones occur where warm air rises, and areas of low pressure develops
These form at the equator and at sub-polar latitudes

15. How are winds and oceans linked?
Cyclones and anticyclones create linked, circulating wind patterns which continually move and change.
The Coriolis effect causes them to spin, either clockwise or counterclockwise, depending on the hemisphere they occur in.
These winds move over the ocean surfaces and cause ocean surface currents

16. Coastal Breezes
Land heats up faster than water. Warm air rises over land, and moves toward the sea. Cooler air from the sea is lower, and moves over the land. This causes coastal breezes.
Onshore breezes blow from the land
Offshore breezes blow from the sea

17. Ocean Currents There are two types of ocean currents:
Surface currents, which are caused by winds
Deeper ocean currents, which are caused by changes in density as a result of changing temperature and salinity

18. How do surface currents work?
The Ekman Spiral
As the wind blows, the molecules on the very surface of the ocean are moved at an angle (not in the same direction as the wind)
The frictional drag on molecules below move the rest of the water at right angles to the wind direction

19. Ekman spiral
describes the speed and direction of flow of surface waters at various depths
Factors:
Wind
Coriolis effect
Ekman transport is the overall water movement due to Ekman spiral
Ideal transport is 90º from the wind
Transport direction (right or left) depends on the hemisphere

20. GYRES
A gyre in oceanography is any large system of rotating ocean currents, particularly those involved with large wind movements.
Gyres are caused by the Coriolis Effect
planetary vorticity along with horizontal and vertical friction, which determine the circulation patterns from the wind curl (torque).
The term gyre can be used to refer to any type of vortex in the air or the sea, even one that is man-made, but it is most commonly used in oceanography to refer to the major ocean systems.

21. Gyres are large circular-moving loops of water Subtropical gyres
Five main gyres (one in each ocean basin):
North Pacific
South Pacific
North Atlantic
South Atlantic
Indian

22. Ocean Gyres: large mounds of water and the flow around them
Ocean Gyres: large mounds of water and the flow around them. They produce large circular currents in all the ocean basins.

23. Gyres

24. Deep Water Circulation (Thermohaline Circulation)
These waters make up the other 90% of the ocean
Move around the ocean basins by density driven forces and gravity.
driven by changes in density
The density difference is a function of different temperatures and salinity
They sink into the deep ocean basins at high latitudes where the temperatures are cold enough to cause the density to increase.
A result of thermohaline processes (changes in temperature or salinity)
Some are vertical, moving water upward and downward to and from the surface (upwelling and downwelling)
Surface and deep-water currents are all linked in a global pattern of circulation.

25. Deep currents Deep currents:
Form in subpolar regions at the surface
Are created when high density surface water sinks
Factors affecting density of surface water:
Temperature (most important factor)
Salinity
Deep currents are also known as thermohaline circulation

26. Upwelling & Downwelling
Upwelling is the movement of cold, deep, often nutrient-rich water to the surface mixed layer;
Downwelling is the movement of surface water to deeper depths.

27. The effect of winds on the vertical movement of water
Upwelling along the coast caused by Ekman transport of waters (waters move to the right of the wind).
The waters moved offshore are replaced by waters from below. This brings cold, nutrient rich waters to the surface
Downwelling caused by Ekman transport onshore (movement of water to the right of the wind direction).

28. Coastal upwelling & downwelling
Ekman transport moves surface water away from shore, producing upwelling
Ekman transport moves surface water towards shore, producing downwelling

29. Upwelling
Upwelling occurs when surface waters diverge (move apart), enabling upward movement of water.
Upwelling brings water to the surface that is enriched with nutrients important for primary productivity (algal growth) that in turn supports richly productive marine ecosystems.
This drives photosynthesis of phytoplankton (tiny alga), which form the base of the ocean food web.

30. What is Downwelling?
When the density of water increases, it sinks below less dense layers of water
Downwelling is the process of accumulation and sinking of higher density material beneath lower density material, such as cold or saline water beneath warmer or fresher water or cold air beneath warm air.
Upwelling is the opposite process and together these two forces are responsible in the oceans for the thermohaline circulation.

31. Downwelling Caused or occurs as a result of 3 situations:
thermohaline processes
Also caused when a current hits a coast
Also occurs beneath mounds of water that form in the middle of anticyclones and gyres
Click here for animation

32. Why are downwelling and upwelling important?
They are needed to revitalize the nutrient and oxygen content in the oceans of the earth
Nutrients and oxygen are brought up from deeper parts of the oceans with cooler water
Warmer water sinks, and picks up more oxygen and nutrients as it cools

33. Other surface currents
Longshore currents
Run parallel along coastlines
Responsible for formation of barrier islands and transport of sand along beaches
Rip currents
Occur when coastal waves or currents converge
Dangerous for swimmers because they flow off the beach towards the open ocean

34. Global Conveyor Belt The ocean is not a still body of water.
There is constant motion in the ocean in the form of a global ocean conveyor belt.
This motion is caused by a combination of thermohaline currents (thermo = temperature; haline = salinity) in the deep ocean and wind-driven currents on the surface.
Cold, salty water is dense and sinks to the bottom of the ocean while warm water is less dense and remains on the surface.

35. Global Conveyor
Colder water at the poles sinks, and moves toward the equator.
As the water warms, it becomes less dense, and rises at the equator (upwelling)
Water from the equator continues to move toward the poles
As water cools near the poles, it becomes more dense and sinks (downwelling)
It takes 1000 years for water to make one loop around the planet
Click here for simulation
Click here for animation

37. The Great Pacific Garbage Patch
What is it?
Island of Floating Plastic; thought to be twice the size of Texas.. But size is still debated
made up of widely dispersed, broken-down plastic waste particles
When plastic bottles, cups and bags are dropped in the street, rain washes them into storm sewers, rivers and eventually the ocean
Stuck in the North Pacific gyre, circulating
it swirls around until sunlight and salt water break it down into small plastic chips. With millions of tons of such trash in the North Pacific Gyre, the water now resembles “plastic soup,”
Fish and birds mistake the plastic bits for food, resulting in death by poisoning or digestive blockage. Plastic also absorbs pollutants like banned PCBs, or polychlorinated biphenyls, once widely used in electrical equipment. When we eat contaminated fish, we ingest these harmful chemicals

39. Ocean Currents http://www.youtube.com/watch?v=Hu_Ga0JYFNg
NASA | The Ocean: A Driving Force for Weather and Climate