Movements of masses of water in the ocean

1

• Movements of masses of water in the ocean

2
Formation of Surface Currents

• The forces that move water to produce ocean
  currents are caused by
• Rotation of the earth
• Winds
• Water density Differences

3
Effect of a Rotating Earth

• Turns from west to east.
• Velocity of rotation at its surface is greatest
  at the equator and least at the poles.
• This is called the Coriolis effect.

4
Effect of Rotating Earth

• Find city of Quito, capital of Ecuador
• Put a sticker on it
• Find Buffalo, NY
• Put a sticker on it
• Use a string to measure the distance around the
  earth beginning and ending at the same city (do
  not cut the string, just mark with your finger)
• Speed distance/time (24 hrs)

5
Understanding the Coriolis Effect

• Read pp. 164 to first paragraph on pp. 167 under
  The Coriolis Effect
• Discuss with your partner until you both
  understand.
• Read pp. 189 (Western Boundary Currents) to pp.
  191 and look at Figure 9.8.
• On a piece of paper, describe the coriolis effect
  and draw a picture
• Which direction does it turn in N. Hemisphere?
• Which direction does it turn in the S. Hemisphere?

6
Coriolis Effect

• Earth spins counterclockwise
• Deflection will always be to the right (looking
  south from N. Pole)
• Air turns to the right in the Northern Hemisphere
• Air turns to the left in the Southern Hemisphere

7
Circulation

• Global circulation of air
• Uneven solar heating
• Rotation of the Earth (Coriolis effect)
• Areas near equator where
• wind converges is known as
• intertropical convergence
• zone (ITCZ)
• Doldrums

8
Wind Patterns

• Trade Winds
• Surface winds that move from latitudes where dry
  air sinks toward latitudes at the equator
• Winds are named by the direction from which
  they blow
• In the N. Hemisphere they are the northeast
  trades
• In the S. Hemisphere they are the southeast
  trades
• Westerlies
• Surface winds that flow between areas where dry
  air sinks toward the latitudes at polar cells
• In N. Hemisphere they approach from the southwest
• In the S. Hemisphere they approach from the
  northwest

9
(No Transcript)
10
Monsoons

• A monsoon is a pattern of wind circulation that
  changes with the season
• Areas that experience monsoons typically have wet
  summers and dry winters
• Land changes temperature more rapidly than the
  ocean
• In spring, land heats faster than the ocean
• Air above the land becomes warmer and rises
• Relatively cool air flows from over the ocean to
  the land to take the place of the warm air, which
  then heats, rises, and forms clouds and rain

11
July
January
12
Breezes

• Breezes are small, daily mini-monsoons
• Sea breezes
• Morning sunlight warms the land, which then warms
  the air above it
• Warm air expands and rises
• Cooler air from over the sea moves toward land
• Land breezes
• After sunset, the land loses heat quickly.
• The air over the still-warm ocean will be warmer
  than air over the cooling land
• The air over the ocean will rise and cooler air
  from the land will move over the ocean

13
(No Transcript)
14
Review

1. Differentiate between trade winds and westerlies.
   (i.e. Where are they located and in what
   direction do they flow...from _____to _____?)
2. Diagram and label sea and land breezes.

15
STOP

• Begin and Finish Storm Powerpoint
• Then continue

16
Ocean Circulation

• Primary forces start water moving and determine
  velocity (speed and direction).
• Thermal expansion and contraction
• Stress of wind blowing over the water
• Density differences
• Secondary forces influence the direction and
  nature of the flow.
• Coriolis effect
• Gravity
• Friction
• Shape of the ocean basins (floor)

17
Surface Currents Solar heating

• Solar (sun) heating causes water to expand
  slightly.
• Sea level near equator is about 8 cm higher than
  sea level moving toward poles.
• This global difference creates a very slight
  slope, and warm equatorial water flows downhill
  toward poles.

18
Surface Currents

• Because the earth is turning west to east, the
  water is deflected to the west
• Waters travel is influenced by the Coriolis
  effect which starts a circular flow

19
Surface Currents - Wind

• Primary force responsible for surface currents
• Trade winds and Westerlies tug on the surface
  of the water
• Water is deflected to the right of the wind
  direction (Coriolis Effect)
• As a rule, the friction of wind blowing for at
  least 10 hours will cause surface water to flow
  at about 2 of wind speed a surface current

20
Ekman Transport

• Coriolis effect spinning of the earth
• Water flows to the right of the direction of the
  wind
• Water in each layer flows a little more to the
  right as you go down
• A down flowing spiral occurs
• Eventually water in one layer will flow in the
  opposite direction of the surface water

21
Gyres circular flow of water

• Coriolis effect deflects water to the right of
  wind direction
• Clockwise in the northern hemisphere
• Counterclockwise in the southern hemisphere
• 5 Major Gyres
• North Atlantic
• South Atlantic
• South Pacific
• North Pacific
• Indian

22
(No Transcript)
23
Western and EasternBoundary Currents

• 5 major ocean gyres flow in relation to the spin
  of the earth geostrophic currents.
• Currents on the western boundary of the ocean
  flow from the equator to the poles
• Currents on the eastern boundary of the ocean
  flow from the poles to the equator

24
Western Boundary Currents

• Fastest and deepest currents
• Move warm water poleward in each hemisphere
• Examples
• Gulf Stream (largest)
• Japan or Kuroshio Current
• Brazil Current
• Aqulhas Current
• East Australian Current

25
(No Transcript)
26
Eastern Boundary Currents

• Carry cold water toward equator
• Shallow, broad, and slower than western boundary
  currents
• Examples
• Canary Current
• Benguela Current
• California Current
• West Australian Current
• Peru or Humboldt Current

27
Countercurrents and Undercurrents

• Countercurrent - Surface water at the equator
  where lack of wind allows it to flow in the
  opposite direction of the main current.
• Without the wind driving the water to the west,
  some backward flow of water occurs here
• Undercurrent water flows beneath and opposite
  of the current over it.
• Undercurrents are why the Galapagos islands are
  in cold water even though they are in the tropics
  near Equator

28
Upwellings

• Form when winds parallel to shore force water
  away from shore west coast of continents.
• Water from the bottom is brought up to replace
  the moved water
• Water brings with it nutrients from the ocean
  bottom
• Cooler water brought upward can create fog banks
  and cool summers (San Francisco)

29
Downwellings

• Form when winds parallel to shore force water
  into shore east coast of continents
• Extra water is forced down towards the bottom
• Helps supply deeper ocean with dissolved gases
  and nutrients

30
Heat transport and Climate

• Currents redistribute heat throughout the globe
• Without these, Earth would have more extreme
  weather.
• Cold water from the poles keeps the Galapogos
  Islands cool even though they are in the tropics
• Warm water from Gulf Stream, warms the air above
  and keeps much of Europe warmer than other places
  at similar latitudes.

31
Galapagos Islands
FROM serc.carleton.edu
32
El Niño Southern Oscillation (ENSO)

• ENSO is a reoccurring natural phenomenon in which
  the Eastern Pacific is warmer than usual causing
  global weather changes.
• Trade winds weaken and warm equatorial water that
  would normally flow west-ward backs up to flow
  east
• Upwellings in California and Peru decrease or
  stop
• Increases Pacific tropical cyclone activity
• Occurs every 3-8 years

33
La Niña

• La Nina is a intense return to the normal
  conditions following strong ENSO
• Colder than normal conditions in California and
  Peru

34
(No Transcript)
35
Deep Ocean Currents
36
Gravitational Currents

• Two forces that explain vertical movement in the
  ocean
• Gravitational Force (G)
• Buoyant Force (B)
• G gt B downward movement sinking
• B gtG upward movement rising
• G B no movement floating at surface
• G B no movement floating neutrally bouyant

37
Thermohaline Circulation

• Water movement caused by differences in
  temperature and salinity.
• Processes that decrease salinity
• Precipitation
• Freshwater run-off
• Processes that increase salinity
• Evaporation
• Freezing

38
Thermohaline Circulation continued . . .