The Ocean General Circulation (satellite)

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The Ocean General Circulation (satellite)
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Mean Circulation in the Ocean
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Mean Circulation in the Ocean
California Current
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Annual mean Salinity Map
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Dissolved Oxygen
Surface
500 meter depth
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Major oceanic circulation systems
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Ocean wind driven circulation
Learning Objectives How does the wind drive
surface currents Upwelling and Downwelling
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Gulf Stream, Plankton Bloom (SeaWiFS, AVHRR)
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Gulf Stream Spiral Eddies
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Mediterranean Sea, Shear Wall Spiral Eddies
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Tropical Atlantic, Spiral Eddy
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Greek Island, Spiral Eddies and Wakes
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Strait of Gibraltar, Solitons
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Eastern Pacific Internal Waves
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Kelvin Waves, from Ships
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Coastal Dynamics
California Filaments and Phytoplankton
Hawaiian Island Wakes
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Some important differences between ocean and
atmosphere
Ocean is heated from above Feels both
Mechanical forcing by the winds Thermal
forcing from the sun Boundaries and complex
geometry associated with continents and bottom
topography, and bathymetry Ocean is denser than
atmosphere Tides Salinity Atmosphere has
clouds and moisture
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How is the energy of the winds transferred to the
ocean?
Ekman Theory
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How does wind force propagate in the ocean?
surface
balance between friction and rotation
100 meter depth
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Ekman Theory and vertical advection in the
ocean COASTAL UPWELLING and DOWNWELLING
OPEN OCEAN EKMAN PUMPING
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Effects of Ekman Currents
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Atmosphere
60
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Ocean
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Sea surface height
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Temperature
Surface
150 meter depth
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Some practical rules to remember
Applies to the Ocean same as Atmosphere!
Fpressure
Low Pressure
High Pressure
FCoriolis

1. Particle will have the Coriolis effect 90 degrees
   to the right
2. Particles will tend to move along line of
   constant pressure
3. Particles will have the high pressure on their
   right (same as Coriolis)

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Glacier melting
Evidence of Global Warming in the Climate System

• Kilimanjaro ice caps are 80 gone since early
  1900s
• All glaciers in tropics are melting rapidly
• Impacts water supply, power generation, tourism,
  local climate and ecology

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Arctic - the most sensitive ecosystem?

• Arctic sea ice has shrunk by 1 million sq km and
  thinned from 3.1m to 1.8m average
• More freshwater, reduced ability to travel over
  ice
• All summer ice gone in this century
• Ecological consequences huge!

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Arctic warming

• Sea ice melting
• Key feedback! (animation)
• Reduces albedo (reflectivity) of earth, allowing
  more radiation to be absorbed
• http//www.gsfc.nasa.gov/topstory/2003/1023esuice.
  html
• Warming temperature
• Melts permafrost
• Ice sheet stability? Key sea level question!
• Rate of warming 8x faster in last 20 years than
  in last 100

1979
2003
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Arctic ecosystems impacts

• Reduced ice less algal production under ice
  undermines base of food chain
• Seal pups emerge just when ice is melting -
  earlier melt means they are exposed before ready
  to thrive
• Caribou need ice to island-hop they are falling
  through as ice thins
• Polar bears hunt on ice in winter, retreat to
  land in summer. Less ice forces them onto land
  earlier

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Higher sea level

• As water warms, it expands (thermal
  expansion).
• Glaciers are melting
• Observation 3mm/yr in past few decades
• Prediction 0.5m rise by the end of this
  century, 2-4m in 500 years

• This will have a major impact on
• Developed coastal regions
• Low-lying island nations
• Intensity of coastal flooding during storm surges
• Coastal ecosystems (e.g. mangroves, estuaries)

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More intense storms
Hurricanes get their energy and staying power
from warm water in the tropical oceans. As
waters get warmer, we expect that hurricanes will
become more intense. Significant change not yet
observed.
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Oceanography and Climate - millennial timescales
Vertical circulation of the ocean
MOVIE The Day After Tomorrow