Chapter 5—Part 1 Ocean Circulation/ Upwelling Zones/ El Niño.
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Transcript of Chapter 5—Part 1 Ocean Circulation/ Upwelling Zones/ El Niño.
Chapter 5—Part 1
Ocean Circulation/Upwelling Zones/
El Niño
Ocean Circulation
1. Eckman spiral
2. Upwelling zones
3. El Niño
• Ocean surface currents are driven by atmospheric winds
• Energy from wind transferred to water by friction
Wind
Wind moves surface water (friction)
Velocity of water decreases with depth
But
• Both the wind and the ocean currents are deflected near the atmosphere-ocean interface by a combina- tion of the Coriolis effect, friction, and gravity
• This gives rise to what is termed the Eckman Spiral - Surface wind rotated 45o relative to the
geostrophic (free troposphere) wind- Surface waters move 45o relative to the surface wind direction- Net transfer of water 90o to the surface wind
The Eckman Spiral
• Surface waters move 45o relative to surface wind• Net transfer of water 90o to surface wind direction
Eckman Pumping
Equator
Surface windSurface currentNet ocean transport
• Surface water is driven offshore by Eckman spiral• Replaced by water from below upwelling!
Geostrophic wind(Easterlies)
Consequences of upwelling
• Deep water is rich in nutrients (P, N, Fe)
• Upwelling brings nutrient-rich water to the surface ocean, fueling biological productivity (phytoplankton)
• Zooplankton eat the phytoplankton
• Fish eat both of these get good fisheries in upwelling zones
El Niño (the Christ child)
Every 3-7 yearsLast 6-18 monthsHappens near Christmas season
El Niño (the Christ child)
Every 3-7 yearsLast 6-18 monthsHappens near Christmas season
Opposite:
La Niña (the girl child)
Normally…
Warm waters pushed by trade winds towards Asia and Australia
Cold waters upwell near South America
http://www.ldeo.columbia.edu/dees/ees/climate/slides/ocean_index.html
Pacificwarmpool
Normal Conditions:
http://www.enn.com/specialreports/elnino/what.asp
• This east-west circulation pattern, which is sort of like a Hadley cell, is called the Walker Circulation
•It reinforces the normal tropical easterlies, thus helping to foster upwelling off the coast of Peru
Australia/Indonesia
South America
Normal Conditions:
El Niño Condition:
http://www.enn.com/specialreports/elnino/what.asp
NormalWalker Circulation
WeakenedWalker Circulation
South America
South America
Australia/Indonesia
Australia/Indonesia
Atmospheric Pressure:
Normal high over Tahiti, low over Darwin, Australia
El Nino low over Tahiti, high over Darwin
The shift in pressure is called the Southern Oscillation
The combined El Niño/Southern Oscillation isreferred to as ENSO
Atmospheric Pressure:Normal high over Tahiti, low over Darwin, AustraliaEl Niño low over Tahiti, high over Darwin
* Darwin
Southern Oscillation Index
[ Pdiff - Pdiffav ] SOI = 10 ----------------------- SD(Pdiff) where
Pdiff = (average Tahiti MSLP for the month) – (average Darwin MSLP for the month),Pdiffav = long term average of Pdiff for the month
in question, andSD(Pdiff) = long term standard deviation of Pdiff
for the month in question.
http://www.bom.gov.au/climate/glossary/soi.shtml
StrongEl Nino
La Niña
http://www.bom.gov.au/climate/current/soi2.shtml
• Is this what is caused the 2011 Texas drought?• “ENSO neutral” conditions persisted during most of 2012
• The fact that we have been in an extended La Niña may explain why the climate has not warmed as fast as expected over the past 15 years…
Total heat accumulation in sea, land, and air
http://www.skepticalscience.com/clarifying-continuation-global-warming.html
Results of El Niño
In the Pacific Region:
weaker trade windswarm waters across the Pacificrain in South America, drought in Australia
Results of El Niño
In the Pacific Region:
weaker trade windswarm waters across the Pacificrain in South America, drought in Australia
Teleconnections--shifting atmospheric patterns (global)
high rain in the US midwestmore storms in the Pacific, fewer in the Atlanticheavy rains in Californiacold winters in the Northeastern US