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The Whole Earth Course

The Whole Earth Course. Chapter 10 Hydrosphere 3 The World Ocean Instructor: Dr. George A. Maul gmaul@fit.edu / X 7453. http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=3827. Outline of the Class. Ocean Geography The Salty Sea Ocean Temperature and Stratification Ocean Circulation

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The Whole Earth Course

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  1. The Whole Earth Course Chapter 10 Hydrosphere 3 The World Ocean Instructor: Dr. George A. Maul gmaul@fit.edu / X 7453 http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=3827

  2. Outline of the Class • Ocean Geography • The Salty Sea • Ocean Temperature and Stratification • Ocean Circulation • BREAK – until Thursday • Ocean Waves • Tides and Sea Level • Ocean Economy

  3. Using a 12" diameter globe, how big is the ocean? The average ocean volume is 1.35 x 1021 liters, or 1.35 x 1018 m3, or 1.35 x 109 km3. The average depth for the oceans is approximately 3.75 km. How big is 1350 million cubic kilometers? What if we made a giant ball of the ocean? How big would it be? 1.35x109 km3 = 4πr3/3 r = ? km How big is that compared to the globe? 686km/6378km = x inches/12 inches, x = about 1.3"

  4. What is the size and shape of Earth? Equatorial radius = 6,378,137 m Polar radius = 6,356,752 m Satellite Altimeter Earth is an oblate spheroid due to rotation, and best represented mathematically by an ellipsoid.

  5. Geoid Surface Topography The geoid is a surface of equal potential energy (PE); a.k.a. an equipotential surface; a.k.a. a “level” surface. PE=M·g·h Departures of the geoid from the ellipsoid.

  6. Bathymetry – the process of determining seafloor topography

  7. Seafloor Topography Where is Earth’s longest mountain range?

  8. How deep is the Ocean? • Mariana Trench Z = 10,924 m • If CSOUND = 1500 m/s, how long does it take for a sound pulse to reach bottom and return? distance = speed x time Units?

  9. Deepsea Sediment TypesWhy are they different? Z ≈ 4000 m CaCO3 dissolves What is calcium carbonate?

  10. Ocean Bottom Pressure? • Mariana Trench Z = 10,924 m • If pressure is hydrostatic, how many atmospheres did the bathyscaphe Trieste have on its hull? 10 m water depth = 1 atmosphere Why? Δp=ρ·g·Δz 101325 Pa = 1025 · 9.8 · Δz

  11. Seasalts What is salinity? Grams salt in one kilogram saltwater.

  12. 84m If we evaporate the ocean, how thick a layer of salt would be left behind? How do we know? 56m ρseawater salinity Column of seawater 5000m x 1m x 1m 28m ρsalt So our column of salt would be about 83m x 1m x 1m.

  13. Solar Heating Distribution of Water and Land Do you remember the value of the solar constant? CSUN= 1368 W·m-2

  14. Rivers 3.6x1016 liters/year

  15. Why do these sea surface salinities vary? E-(P+R)

  16. COULD THE OCEAN DISSOLVE MORE SALT? SALINITIES IN GREAT SALT LAKE EXCEED 270 g/kg!! Dead Sea salinities ≈ 33.7% = 337 ‰.

  17. Sea surface temperatures (SST) in the world ocean during August. Why do these sea surface temperatures vary? Tmax =57°C Tmin= -88ºC H= m·CP·ΔT

  18. Depth zones in the ocean Can you explain why these profiles appear like they do?

  19. The previous figure is an average distribution of temperature, salinity and density. However, the surface values are variable with both latitude and season. Here we see the average annual temperature by latitude. Why do they differ?

  20. Ocean Circulation has two components Thermohaline (deep) Wind driven (surface)

  21. AverageGlobal Winds

  22. Global Winds and E-(P+R)

  23. Satellitederivedsurfacewinds Wind stress (tau) τ = ρairCDV2 Units? Satellite scatterometer

  24. THE WIND-DRIVEN CIRCULATION: Surface ocean currents form a distinctive pattern, curving to the right (clockwise) in the northern hemisphere and to the left (counterclockwise) in the southern hemisphere. Benjamin Franklin’s Map Computer Model Map

  25. Coriolis Effect http://www.youtube.com/watch?v=_36MiCUS1ro Coriolis Parameter f = 1.4584 x 10-4 sin ø, where øis the symbol for latitude. Where does 1.4584 x 10-4 come from?

  26. Coriolis Parameter (f) Earth rotates 2π radians in 23h56m4.1s one sidereal day. units? 0.729x10-4 On a rotating planet, centrifugal force is Ω2R, where R is the radius at that latitude. Now if a parcel moves eastward at speed U, there is an added angular velocity U/R. The new total force: Coriolis force

  27. Forces affecting seawater • Acceleration = • Pressure gradient force + • Coriolis force + • Gravity + • Friction Infrared Image of Florida Current

  28. Units (all force/unit mass) =? ΣF=ΣM∙a

  29. Major Balance of Forces Horizontal: geostrophic balance pressure gradient vs. Coriolis z - up Vertical: hydrostatic balance pressure gradient vs. gravity Cartesian Coördinates y - north x - east Rene Descartes

  30. Global Sea Surface Dynamic Topography Not the Geoid!

  31. Horizontal Pressure Gradient Force sea surface h2 h1 level surface (geoid) p1 p2 Δx Units?

  32. Geostrophic Currents(pressure gradient force balances Coriolis force) If Δh = 1 m in Δx = 100 km, and ø= 43.28934 °N, what is the geostrophic velocity vg (speed and direction)? w - upward Units? v - northward Direction u - eastward

  33. Sea Surface Dynamic Topography Variability Break! See you Thursday Break! See you Thursday

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