Introduction to Oceanography Lecture 12, Current 2

NOAA Ocean-Atmosphere Sea Surface Temperature Model, Public Domain, http://www.gfdl.noaa.gov/visualizations-oceans

Coriolis “Geostrophic” Response L H

WESTERLIES

Horse LatitudesH ~ 30o N

TRADE WINDS

H L

Figures, UCLA

1 Coriolis “Geostrophic” Response

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

Average satellite-measured “hill” of water at western side of gyre. Why isn’t the high pressure in the center of the ocean?

QUESTIONS?

Gene Paull, UT Brownsville, Public Domain(?), http://upload.wikimedia.org/wikipedia/commons/0/06/Corrientes-oceanicas.gif

2 Major Current Systems 1. 2. South Atlantic gyre 3. 4. 5. Indian 6. Antarctic Circumpolar Current • Not a gyre!

Major Current Systems

N. Atlantic N. Pacific

S. Pacific Indian S. Atlantic

Gene Paull, UT Brownsville, Public Domain(?), http://upload.wikimedia.org/wikipedia/commons/0/06/Corrientes-oceanicas.gif

3 Currents on each edge of a Gyre have names. Transverse Current

Eastern

Boundary 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

4 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

5 Western Boundary Currents

Cold, cold Northern Canada Temperate Northern Europe

British National Centre for Ocean Forecasting, Public Domain(?), http:// www.nerc-essc.ac.uk/ ncof/mersea/css-gif/ Mapwithrectangle.gif

Redhttp://www.itrd.gov/pubs/blue96/images/temp.atlantic.gif -- Warm surface water Blue -- Cold surface water

North Atlantic Gyre Boundary Currents

100

50

Sea Surface 0 Height (cm) 0 500 1000 1500 2000 2500 -50 Distance (km)

6 Coriolis “Geostrophic” Response

Centers of gyre “hills”: , W. Pacific, Madagascar, etc. 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

7 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); (N. Pacific); (S. Atlantic); (Indian); (S. Pacific) • Gulf Stream is king of them all! 2 m/s ≈ 200 km/day 55x106 m3/sec = 55 Sverdrups transported > 3000 Mississippi Rivers!

8 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 • (N. Atlantic); (N. Pacific); (S. Atlantic); (Indian); Peru Current (S. Pacific)

Boundary Currents

Current Width (km) Depth (km) Flow Rate (km/day)

Western < 100 km 1-2 km ~ 100 km/ Boundary day

Eastern > 1000 km < 0.5 km ~ 10 km/ Boundary day

9 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

10 of Deep Water

British National Centre for Ocean Forecasting, Public Domain(?), http:// www.nerc-essc.ac.uk/ ncof/mersea/css-gif/ Mapwithrectangle.gif 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.

CORIOLIS

N. Equ. Current

Equator UPWELLING S. Equ. Current

CORIOLIS

Figures, UCLA

11 Equatorial Pacific Upwelling

UPWELLING

Chris Henze, NASA Ames, Public Domain, http:// people.nas.nasa.g ov/~chenze/ECCO/ 93-02.T_1.raw.mpg

Blue-Yellow - Cold water Red-Magenta - Warm water

Coastal Upwelling

• Coastal : away from shoreline forces upwellings

CORIOLIS UPWELLING

Figures, UCLA

12 Coastal upwelling, California

California

NOAA image, Public Domain, http://oceanexplorer.noaa.gov/explorations/02quest/background/upwelling/media/ Fig1_cartoon.html

Upwelling and Downwelling Flows • Antarctic Divergence:

– 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 Chlorophyll a productivity Concentration

NASA image, Public Domain, http://earthobservatory.nasa.gov/Study/Polynyas/

13 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

14 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

Where does deep water come from? Labrador Sea

Weddell Sea

Adapted from figure by Helen Hill(?), MIT, http://puddle.mit.edu/~helen/

15 Deep Water Formation

Deep currents – sinking of dense water near the poles

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

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

16 Water Mass Classifications Intermediate Waters: Water between cold, deep polar water and surface Example: Mediterranean outflow: Warm and highly saline at ~1000 m 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 Sea-surface salinity map by Rosarinagazos, Creative Commons A S-A 3.0, http://commons.wikimedia.org/wiki/File:Wiki_plot_04.png

Strait of Gibraltar

%

• • • • • • • • •

Atlantic Deep Circulation

UCAR/NOAA/NASA, Public Domain, http:// www.meted.ucar.edu/ tropical/met_topics/ media/graphics/ moc_atlantic_salinity. jpg MIW – Mediterranean Intermediate Water

Antarctic Intermediate Water MIW

North Atlantic Deep Water Antarctic Bottom Water

17 Pacific

0 0 0 0 0 0

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

18 Hannes Grobe, Wikimedia Commons, Creative Commons A S-A 2.5, http://upload.wikimedia.org/wikipedia/ commons/2/2c/Antarctic_bottom_water_hg.png

QUESTIONS?

Excellent vintage 1960’s fluid dynamics movies: National Committee for Waves Fluid Mechanics Films http://web.mit.edu/hml/ncfmf.html

Hurricane wavemaker, Hinsdale Wave Research Laboratory, Oregon State University, http://oregonstate.edu/ media/twvwz-hiq

19 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

20 The Dynamics of a Wave Wave Period – time between crests Wave Frequency – number of crests per second Wave Speed – rate crests move (meters/second)

Animation courtesy Dr. Dan Russell, Kettering University, http:// paws.kettering.edu/ ~drussell/Demos/wave-x-t/ wave-x-t.html

Period, frequency, speed and wavelength are related!

Period = 1/frequency Speed = wavelength / period = wavelength x frequency

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 from National Weather Service/NOAA, Movie by Patricia E. Videtich and Erik J. Crooks Public Domain, http://www.srh.noaa.gov/ http://faculty.gvsu.edu/videticp/waves.htm jetstream//ocean/wave_max.htm

21