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Coriolis “Geostrophic” Response L H 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. 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! 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 Gulf Stream 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”: Sargasso Sea, 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); 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! 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 • 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 < 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 Upwelling 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 Upwellings: Ekman transport 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 .
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