Title: Oceanic Circulation
1Oceanic Circulation
- I. How oceans work
- II. Surface currents
- III. Deep Currents
- IV The Air-Sea Interactions (ENSO)
2The Role of Oceans in Global Climate Variability
3The Role of Oceans in Hydrological Cycle
97 of the Earths free water 86 of the global
evaporation 78 of global precipitation
4I. How oceans work
- Area covers 70 of the Earths surface
- Volume 97 of all the water on the Earth
- Depth 4 kilometers
- Density 1034-1035 kg/m3 (Pure water 1000 kg/m3)
over 90 of the ocean. Depends on temperature and
salinity. - cold water ? high density
- loss of water by evaporation ? increase salinity
? high density - precipitation and river discharge ? decrease
salinity ? low density - Heat capacity high
- Temperature less variable than in the atmosphere
- Freezing point 1.9C, not at 0C because of
salinity - Surface is not level due to currents, waves,
atmospheric pressure differences, and variations
in gravity. - Two main forms of circulation
- wind-driven circulation (horizontal, surface
waters, fast) - thermohaline circulation (vertical, deep waters,
slow)
5I. How oceans work (Contd)
6Relative proportions of dissolved salts in
seawater
7Annual Mean Ocean Surface Temperature
8Annual Zonal Mean Ocean Surface Temperature
9Annual Mean Ocean Surface Salinity
10Annual Zonal Mean Ocean Salinity
11Ocean Meridional Overturning (Global)
12Ocean Meridional Overturning in Atlantic
13I. How oceans work (Contd)
A. Heated primarily by Sun, largely at the
Equator, with global heat transfer by ocean
currents ? profound effect of oceans on
climate B. Two overall layers 1. Thin, warm, less
dense surface layer well mixed by turbulence
generated by wind 2. Thick, cold, more dense deep
layer that is calm and marked by slow currents 3.
Thermocline is the boundary between the layers
14Mixed Layer Processes
Vigorous mixing processes lead to uniform
conditions within the surface mixed layer.
15Mixed Layer Processes
16I. How oceans work (Contd)
17Quiz
1. Which of the following is NOT true about the
oceans? A. Approximately 97 of the total
water on Earth is located in the oceans B.
The oceans cover about 70 of Earths surface
C. The average depth of the oceans is about 4
km. D. The sea surface is level for all the
oceans. E. Because it takes far more energy
to change the temperature of water than land or
air, water warms up and cools off much more
slowly than either. 2. The three largest
reservoirs of water at the earths surface in
decreasing order of volume are A. oceans, ice
caps/glaciers, and ground water B. oceans, ice
caps/glaciers, and soils C. oceans,
lakes/rivers, and soils D. oceans, atmosphere,
and biosphere E. oceans, ground water, and
soils 3. What is the primary salt in the ocean?
A. methane B. CO2 C. FeO2 D. CaSO4 E.
NaCl 4. Which of the following increase
salinity? A. Evaporation B. Precipitation. C.
Formation of sea ice. D. River runoff. E. A
and C only.
18II. Surface currents
19II. Surface currents
- A. Three primary forces
- Global wind patterns cause surface ocean currents
because of frictional drag - 2. Coriolis effect
- 3. Pressure gradients
20B. Global wind patterns cause surface ocean
currents because of frictional drag
July
- Creation of waves
- 2. Creation of hemisphere-scale gyres
-
- 3. Decrease in current speed with depth
January
21C. Coriolis effect
- 1. Earth rotation speed is greatest at Equator
falling to zero at Poles - 2. Conservation of angular momentum
- a. Deflection to the right for component of
Equator-to-Pole flow in Northern Hemisphere - b. Deflection to the left for component of
Equator-to-Pole flow in Southern Hemisphere
22C. Coriolis effect (Contd)
- 3. Creation of Ekman Spiral
- a. To depth of 100 m
- b. Surface current moves 20-45o from the wind
direction (45o in theory) - c. Deflection increases with depth, forming a
spiral - d. Net transport of water is 90o from the wind
direction -
23C. Coriolis effect (Contd)
- 3. Creation of Ekman Spiral
- a. To depth of 100 m
- b. Surface current moves 20-45o from the wind
direction (45o in theory) - c. Deflection increases with depth, forming a
spiral - d. Net transport of water is 90o from the wind
direction -
24D. Pressure gradients
- 1. Differences in water height (i.e., piling of
water against a continent because of the wind) - 2. Density differences because of temperature or
salinity - 3. Atmospheric pressure differences
- E. Geostrophic currents - balance of Coriolis
force by pressure gradient - F. Land forms barriers to global ocean currents
25G. Resultant overall current pattern
- 1. Currents converge toward Equator following
Trade Winds and ITCZ - 2. Westward flow along Equator (i.e., North and
South Equatorial Currents) - 3. Equatorial Currents turn poleward where they
encounter land barriers (e.g., Gulf Stream) - 4. Eastward flow of currents is enhanced by the
Westerlies - 5. Currents turn toward the Equator where they
encounter land barriers, completing the gyres
26Effects of surface currents
- 6. Significant heat transfer
- a. More solar heating and evaporation at Equator,
less at Poles ? salinity and temperature
Equator/Pole gradient - b. Warm and salty water carried poleward
27Effects of surface currents
- 7. Zones of upwelling
- a. Deflection of water away from continent
- b. Upwelling of deeper water to replace surface
water - c. Commonly nutrient rich
287. Zones of upwelling
29III. Deep Currents
- A. Thermohaline-driven currents
- 1. Greater salinity ? greater density
- 2. Lower temperature ? greater density
- 3. Equilibrium is sought in global-scale deep
currents (conveyor belt)
30B. Global Conveyor Belt (Contd)
- 1. Warm and salty shallow water from Tropics is
carried northward through Atlantic - 2. Water cools in North Atlantic and sinks east
of Greenland as cold and salty dense water - 3. North Atlantic Deep Water flows toward the
Equator and into the South Atlantic, where it
meets yet colder and denser Antarctic Bottom
Water flowing toward the Equator
2
1
3
31B. Global Conveyor Belt (Contd)
- 4. Combined flow eastward below Africa and into
the Pacific Ocean - 5. Deflected by Asia
- 6. Journey through Pacific causes warming and
slow rise to surface - 7. Warm and less dense Pacific surface waters
move south and west to converge toward Equator as
shallow surface water to continue warming
6
5
7
4
32B. Global Conveyor Belt (Contd)
- 8. 1,000 years for a complete cycle
- 9. Conveyor Belt aided by imbalance between loss
of water by evaporation in Atlantic and gain of
water by precipitation and runoff - 10. Bering Strait prevents free exchange between
Arctic and Pacific Oceans ? inhibits
Arctic-Pacific Conveyor Belt
33The Role of Oceans
- I. How oceans work
- II. Surface currents
- III. Deep Currents
- IV The Air-Sea Interactions (ENSO)
34The Air-Sea Interactions
A. Inter-Tropical Convergence Zone (ITCZ) B. El
Niño - Southern Oscillation, aka ENSO El
Niño Spanish for boy child Christ child
referring to warm water conditions and associated
consequences, frequently occurring around
Christmas Southern Oscillation A seesaw
pattern of reversing surface air pressures at
opposite ends of the Pacific Ocean Walker
Circulation (zonal convection) refers to the
localized zonal (west-east) convection cell of
atmospheric circulation above the Pacific Ocean.
The easterly trade winds are part of the
low-level component of the Walker circulation.
C. La Niña (girl child) Opposite extreme of
El Niño
35A. Inter-tropical Convergence Zone (ITCZ)
1.What is ITCZ? Region near the equator where
the wind systems (trade winds) of the Northern
Hemisphere and Southern Hemisphere meet. 2.
Position changes with season. North of equator in
July, (generally) south of equator in
January. 3. Broad trough of low pressure,
typical of cloudiness, thunderstorm, and heavy
precipitation. 4. More intensely developed in
the western Pacific because of warm water pool of
surface seawater (T 31 C) and Asian
monsoons. 5. Influences the ocean currents and
salinity.
36El NinoHow itWorks
37Known for over 400 years ...
38Occurs during Christmas season ...
- Christ Child
- The Boy
- The Little One
39Food Chain
40B. El Niño - Southern Oscillation, a.k.a. ENSO
1.What is ENSO? ENSO is a periodic climatic
phenomenon caused by ocean-atmosphere dynamics in
the tropical Pacific Ocean.
ENSO Process Every two to seven years, strong
westward-blowing SE trade winds subside. Warm
water moves back eastward across the Pacific,
like water shifting in a giant bathtub. The warm
water and shifting winds interrupt the upwelling
of cool, nutrient-rich water.
41El Niño and SOI
El Niño Noticed at Christmas time by Peruvian
fisherman warm coastal waters leading to poor
fishing
El Niño / Southern Oscillation an oscillation
in the surface pressure (atmospheric mass)
between the SE tropical Pacific and the
Australian-Indonesian regions.
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43Reading the Index
442. Importance of understanding ENSO
a. Severe rapid climate variations caused by El
Niño are natural b. El Niño has important
consequences for famine and economics around the
globe.
45 3. Basics of ENSO
Western equatorial Pacific has some of the
world's warmest ocean water. To the east, cool
water wells up, carrying nutrients (see Oceans
lecture) that support large fish populations
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47Oscillation of surface water in the Pacific
48What causes ENSO? large-scale internal waves
49What Causes ENSO?
During the warm phase of ENSO (El Niño phase) the
West Pacific Warm Pool and its associated low
pressure atmospheric center migrate to the east
along the equator. The water is transported by
these internal waves. Kelvin waves cross the
Pacific in 2-3 months and lead to a warming of
the surface waters and rise in sea level along
Peru.
50What Causes ENSO?
As sea level rises and warm water accumulates in
the eastern Pacific, Rossby waves are generated
that move west across the Pacific. The time it
takes for these waves to cross the Pacific is
strongly dependent on the latitude at which the
wave is traveling (near the equator, they take a
9 month journey 12 degrees from the equator,
they take 4 years). The Rossby waves reach the
Western Pacific, travel along the coast as Kelvin
waves to the equator and turn east and begin
another crossing of the Pacific.
515. If its a tropical phenomenon, why does it
affect us in Texas?
Teleconnection during ENSO, warmer, moister air
than usual is generated in the eastern part of
the ITCZ in the Pacific. This changes
atmospheric circulation patterns and deflects the
jet stream that goes west-east across US at a
more easterly longitude than during non-ENSO
year. As a result, different amounts of moisture
and heat than usual are delivered to different
parts of the world
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56El Nino and Texas
57El Nino and Texas
- December - March TX wetter and cooler
- More wet and cool in S. Texas
- Experience flooding, high number of storms
originating from Gulf of Mexico and tropical
Pacific because of the strengthened subtropical
jet stream - Protect your property homeowners insurance
586. Whats good and bad about the effects of
ENSO?
- This depends on where you live and what your
lifestyle is
59b. 1997-1998 event and the medias response
607. Measuring El Nino
61Measuring El NinoWeather Stations
- Stevenson Screen
- Temperature
- Precipitation
62Weather Station Colorado
63Measuring El NinoBuoys
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67Measuring El NinoSatellites
68Satellites Temperatures
69Measuring El NinoSea Surface Temperatures
70Measuring El NinoCoral Bleaching
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