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Introduction to Oceanography
NOAA Ocean-Atmosphere Sea Surface Temperature Model, Public Domain, http://www.gfdl.noaa.gov/visualizations-oceans
Lecture 12, Current 2 Coriolis “Geostrophic” Response
WESTERLIES
Horse Latitudes ~ 30o N
TRADE WINDS
H
HL
L
H
Figures, UCLA
Coriolis “Geostrophic” Response
Average satellite-measured “hill” of water at western side of gyre. Why isn’t the high pressure in the center of the ocean?
Mean 1992-2002 dynamic ocean topography, Nikolai Maximenko (IPRC) and Peter Niiler (SIO), Public Domain, http://apdrc.soest.hawaii.edu/projects/DOT/1992-2002MDOT.jpeg
QUESTIONS?
Gene Paull, UT Brownsville, Public Domain(?), http://upload.wikimedia.org/wikipedia/commons/0/06/Corrientes-oceanicas.gif
Major Current Systems 1. North Atlantic gyre 2. South Atlantic gyre 3. North Pacific gyre 4. South Pacific gyre 5. Indian Ocean gyre 6. Antarctic Circumpolar Current
• Not a gyre!
Gene Paull, UT Brownsville, Public Domain(?), http://upload.wikimedia.org/wikipedia/commons/0/06/Corrientes-oceanicas.gif
Major Current Systems
N. Pacific
S. Pacific S. Atlantic
N. Atlantic
Indian
2
Currents on each edge of a Gyre have names. W
este
rn
Bound
ary C
urre
nt
East
ern
Boun
dary
Cur
rent
Transverse Current
Transverse Current
Cropped from Gene Paull, UT Brownsville, Public Domain(?), http://upload.wikimedia.org/wikipedia/commons/0/06/Corrientes-oceanicas.gif
Transverse Currents • Driven primarily by Wind Stress • Antarctic Circumpolar Current is the
largest of these
Gene Paull, UT Brownsville, Public Domain(?), http://upload.wikimedia.org/wikipedia/commons/0/06/Corrientes-oceanicas.gif
Antarctic Circumpolar Current Not a gyre!
Southern Westerlies drive largest volume current on Earth – 100 x 106 m3/s on average.
– 600 times the flow of the Amazon!
– WHY? • Constant strong westerly winds
• No continents to disrupt flow in southern ocean • Home of the most violent seas on Earth
Storm waves, Southern Ocean, R. Easther, Australian Antarctic
Division, http://www.aad.gov.au/default.asp?casid=2341
Equatorial Currents • Found on either side of the equator • Flow to the west
Gene Paull, UT Brownsville, Public Domain(?), http://upload.wikimedia.org/wikipedia/commons/0/06/Corrientes-oceanicas.gif
Western Boundary Currents
http://www.itrd.gov/pubs/blue96/images/temp.atlantic.gif
Gulf Stream
TemperateNorthernEurope
Cold,cold Northern
Canada
Red -- Warm surface water Blue -- Cold surface water
British National Centre for Ocean
Forecasting, Public Domain(?), http://
www.nerc-essc.ac.uk/ncof/mersea/css-gif/Mapwithrectangle.gif
North Atlantic Gyre Boundary Currents
-50
0
50
100
0 500 1000 1500 2000 2500
Sea Surface Height (cm)
Distance (km)
3
Centers of gyre “hills”: Sargasso Sea, W. Pacific, Madagascar, etc.
Coriolis “Geostrophic” Response
Animation from the Naval Research Laboratory, Public Domain, http://www7320.nrlssc.navy.mil/modas2d/anims/gbl/httot_gbl_12mon.fli
Gulf Stream
Current flow rate in the Gulf Stream, in units of 106 m3/sec (roughly: millions of tons/sec)
106 m3/sec = 60 Mississippi Rivers! Image from Sverdrup, Johnson, and Fleming, Sverdrup H.U., Johnson M.W., Fleming R.H. The Oceans.. their
physics, chemistry, and general biology (1942), http://oceanworld.tamu.edu/resources/ocng_textbook/chapter11/Images/Fig11-7.htm
Gulf Stream time-lapse Surface Temp.
U. Miami /CIMAS, Public Domain. http://oceancurrents.rsmas.miami.edu/atlantic/img_rrsl/sst-composit.avi
Western Boundary Currents
• Fastest, deepest gyre currents – Equatorial currents are deflected to high latitudes by
continents – Transport warm water to high latitudes
• Gulf Stream (N. Atlantic); Kuroshio Current (N. Pacific); Brazil Current (S. Atlantic); Agulhas Current (Indian); East Australian Current (S. Pacific)
• Gulf Stream is king of them all! 2 m/s ≈ 200 km/day 55x106 m3/sec = 55 Sverdrups transported
> 3000 Mississippi Rivers!
Eastern Boundary Currents
• Shallow, broad, slow currents – Return flow to low latitudes – Transport cold water to the equator – Roughly 1/10 the speed of WBCs
• Canary Current (N. Atlantic); California Current (N. Pacific); Benguela Current (S. Atlantic); West Australian Current (Indian); Peru Current (S. Pacific)
Boundary Currents
Current Width (km) Depth (km) Flow Rate (km/day)
Western Boundary
< 100 km 1-2 km ~ 100 km/day
Eastern Boundary
> 1000 km < 0.5 km ~ 10 km/day
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Important non-gyre currents: Equatorial Counter Currents
• Right between the two Equatorial currents • No Coriolis at equator: only wind stress vs.
pressure • Response of water to constantly being
pushed / piled up on the west side of the basin (up to 50 cm high)
• Tends to flow back towards East.
QUESTIONS?
Gene Paull, UT Brownsville, Public Domain(?), http://upload.wikimedia.org/wikipedia/commons/0/06/Corrientes-oceanicas.gif
British National Centre for Ocean
Forecasting, Public Domain(?), http://
www.nerc-essc.ac.uk/ncof/mersea/css-gif/Mapwithrectangle.gif
Upwelling of Deep Water
Red -- Warm surface water Blue -- Cold surface water
Sites & Causes of Upwelling • Equatorial Divergence: Opposite
Coriolis bending on each side of the equator causes pull surface water away. Cold deep water rises to replace it.
Equator
N. Equ. Current
S. Equ. Current
CORIOLIS
CORIOLIS
UPWELLING
Figures, UCLA
Equatorial Pacific Upwelling
UPWELLING
Blue-Yellow - Cold water Red-Magenta - Warm water
Chris Henze, NASA Ames, Public Domain, http://people.nas.nasa.gov/~chenze/ECCO/93-02.T_1.raw.mpg
Coastal Upwelling
• Coastal Upwellings: Ekman transport away from shoreline forces upwellings
UPW
ELLI
NG
CORI
OLI
S
Figures, UCLA
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California
Coastal upwelling, California
NOAA image, Public Domain, http://oceanexplorer.noaa.gov/explorations/02quest/background/upwelling/media/Fig1_cartoon.html
Upwelling and Downwelling Flows • Antarctic Divergence:
NASA image, Public Domain, �http://earthobservatory.nasa.gov/Study/Polynyas/
Chlorophyll aConcentration
– Two causes: Dense sinking waters (vertical mixing) and Ekman transport (upwelling) away from Antarctic Circumpolar Current – Results in intense upwelling around Antarctica – Very high biological productivity
Liusen Xie, UBC Climate Prediction Group, http://www.ocgy.ubc.ca/projects/clim.pred/Upwell/annualL.jpg
QUESTIONS?
Gene Paull, UT Brownsville, Public Domain(?), http://upload.wikimedia.org/wikipedia/commons/0/06/Corrientes-oceanicas.gif
Deep Currents in the Ocean • Two Types
– Surface Currents • Mixed layer (0-300 m), most surface currents
here • Pycnocline (to 1000m)
– Sub-surface (deep) Currents • Deep water
American Meteorological Society, http://oceanmotion.org/images/
ocean-vertical-structure_clip_image002.jpg
Labrador Sea
WeddellSea
Where does deep water come from?
Adapted from figure by Helen Hill(?), MIT, http://puddle.mit.edu/~helen/
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Deep Water Formation
Figure from Matthew England, Climate Change Research Centre (CCRC) University of New South Wales, http://web.maths.unsw.edu.au/~matthew/southern_ocean_variability.htm
Deep currents – sinking of dense water near the poles
Water Mass Classifications • Deep Waters:
– North Atlantic Deep Water (NADW) • Vertical mixing & incorporation of salty N.
Atlantic waters near Greenland
• Bottom Waters: – Antarctic Bottom Water (AABW)
• Forms dominantly in Weddell Sea in regions of active sea ice formation (polynyas)
• Cold, saline sinking water • Densest water mass in the oceans
Water Mass Classifications Intermediate Waters: Water between
cold, deep polar water and surface Example: Mediterranean outflow:
Warm and highly saline at ~1000 m
%
• • • • • • • • •
Sea-surface salinity map by Rosarinagazos, Creative Commons A S-A 3.0, http://commons.wikimedia.org/wiki/File:Wiki_plot_04.png
Med. outflow figure by G. P. King, http://www.eng.warwick.ac.uk/staff/gpk/Teaching-undergrad/es427/rice.glacier.edu-oceans/
GLACIER%20Oceans-%20--%20Densitydriven.htm
Strait of Gibraltar
Atlantic Deep Circulation
MIW
North Atlantic Deep Water
Antarctic Intermediate Water
Antarctic Bottom Water
MIW – Mediterranean Intermediate Water
UCAR/NOAA/NASA, Public Domain, http://www.meted.ucar.edu/tropical/met_topics/media/graphics/moc_atlantic_salinity.jpg
0 0 0 0 0 0
Pacific
UCAR/NOAA/NASA figure, Public Domain, http://www.meted.ucar.edu/oceans/currents/media/graphics/pacific_salinity_section.jpg
Global deep water ‘conveyor’
Robert Simmon/Robert Rohde, NASA/Wikimedia, Public Domain, http://en.wikipedia.org/wiki/File:Thermohaline_Circulation_2.png
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QUESTIONS?
Hannes Grobe, Wikimedia Commons, Creative Commons A S-A 2.5, http://upload.wikimedia.org/wikipedia/commons/2/2c/Antarctic_bottom_water_hg.png Waves
Hurricane wavemaker, Hinsdale Wave Research Laboratory, Oregon State University, http://oregonstate.edu/media/twvwz-hiq
Excellent vintage 1960’s fluid dynamics movies: National Committee for Fluid Mechanics Films http://web.mit.edu/hml/ncfmf.html
Waves • Traveling disturbances of the water column • Waves move but there is little or no net transport of
the water – If you put dye in the water, a wave can pass through and the
dye will basically remain in place • Most familiar are wind waves - produced on the ocean
surface by effects of time-varying winds
Animation courtesy Dr. Dan Russell, Kettering
University, http://paws.kettering.edu/
~drussell/Demos/waves/wavemotion.html
The Anatomy of a Wave
Remember These! Adapted from figure by Kraaiennest, Wikimedia Commons, Creative Commons A S-A 3.0, http://
commons.wikimedia.org/wiki/File:Sine_wave_amplitude.svg
The Dynamics of a Wave
Wave Frequency –
number of crests per second
Wave Speed – rate crests move (meters/second)
Wave Period – time between
crests
Period, frequency, speed and wavelength are related! �
Period = 1/frequencySpeed = wavelength / period = wavelength x frequency
Animation courtesy Dr. Dan Russell, Kettering University, http://
paws.kettering.edu/~drussell/Demos/wave-x-t/
wave-x-t.html
Oscillation • As waves travels through, water
locally moves in circular orbits • Like a seagull bobbing on water
surface • In most cases the water, like the
seagull, ends up back where it started (little or no net transport).
Movie by Patricia E. Videtich and Erik J. Crooks �http://faculty.gvsu.edu/videticp/waves.htm
Movie from National Weather Service/NOAA, Public Domain, http://www.srh.noaa.gov/
jetstream//ocean/wave_max.htm