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U4735x Environmental Science for Decision Makers

Lecture 5: Ocean atmosphere circulation, El Niño and other regional phenomena: how these systems redistribute heat.

James D. Hays

I. Properties of water.

  1. Shape of the water molecule (Fig 1).

  2. Heat of fusion and heat of vaporization.

  3. Why water is a good solvent (Fig 2).

  4. The hydrogen bond and life (Fig 3).


II. Buoyancy of fluids.

  1. Fluids are both gases and liquids.

  2. Fluids have no strength.

  3. Liquids.
    1. The pressure on the walls of a container holding a liquid is proportional to the depth of the liquid (Fig 4).
    2. Forces within a liquid (Fig 5).
      1. Cube with the same density as the liquid.
      2. Cube with twice the density of the liquid.
      3. Cube with half the density of the liquid.

  4. Gases.
    1. Gases are compressible.
      1. What happens when you compress a gas?
      2. Pressure with depth within a gas (Fig 6).
    2. Buoyancy of a gas.
      1. Same calculation as with a parcel of water.
      2. Balloon with a gas less dense than air.
        1. Helium for example.
          1. If balloon does not expand, it will rise to some level where the helium inside has the same density as the air outside.
          2. If balloon expands, it will continue to rise until it bursts.
        2. Hot air - if balloon expands, air cools. The rate of cooling os 9.8°C per kilometer. This is known as the dry adiabatic lapse rate. Vertical temperature profile of the atmosphere (Fig 7).
        3. Why does the atmosphere preserve this profile? (Fig 8)
        4. Images of the Limb of the Earth and thunderheads (Fig 9 and Fig 10).


III. General Circulation of the Atmosphere

  1. The surface of the Earth drives both the atmospheric and oceanic circulation. Heated by the sun and the Earth's atmosphere, this energy and resulting temperature contrasts drive the circulation of the Earth's surface fluids.
    1. Heating causes fluids to become less dense.
    2. A stable vertical structure for a fluid is less dense above and more dense below. Less dense floats easily on more dense fluids. Thus heating the top of the ocean makes it stable while heating the bottom of the atmosphere makes it less stable.

  2. Differential heating of the Earth (Fig 11 and Fig 12).

  3. Circulation of the atmosphere on a non-rotating Earth (Fig 13).

  4. The Coriolis effect.

  5. Hadley cell circulation (Fig 14).

  6. Northern and Southern atmospheric circulation (Fig 15).

  7. Where does it rain? (Fig 16 and Fig 17).

  8. Why do we have seasons? (Fig 18)

  9. The Earth from space (Fig 19).

 

IV. The surface circulation of the ocean.

  1. Wind driven surface circulation of the ocean (Fig 20, Fig 21).

  2. Areas of upwelling and downwelling (Fig 22).

  3. Ocean productivity (Fig 23).

  4. Temperature structure of the near surface ocean (Fig 24).

  5. Equatorial Pacific atmospheric and oceanic circulation. (See Fig 20, Fig 21).

    1. East-west structure of near surface Pacific (Fig 25).

    2. General characteristics of the atmosphere and oceanic circulation of the equatorial Pacific (Fig 26).

    3. EL NINO circulation.

      1. Initial growth of El Nino (Fig 27).

      2. Demise of El Nino (Fig 28).

      3. Major consequences of El Nino.

        1. Rains in Indonesia.

        2. Rains in western South America.

V. Deep Circulation of the Ocean.

  1. Circulation driven by differences in density of sea water.

    1. Causes of differences in density of sea water.

      1. Temperature.

        1. Providing salinity doesn't change, lowering sea water temperature causes sea water to become more dense.

        2. Range of temperature in the ocean is -1.9 to 42 degrees Celsius.

        3. Since the ocean is heated from above and warm water is less dense than cold, the temperature in the ocean generally decreases with depth.

      2. Salinity.

        1. Salinity is the total amount of solid matter dissolved in sea water - not including organic matter - in parts per thousand. The average salinity of the ocean is 34.7 parts of dissolved material in a thousand parts of water. Therefore, a thousand grams (one kilogram) of sea water would contain 34.7 grams of dissolved chemical components. The concentration of salts in the sea is fairly constant. Ninety-nine percent of the salts consist of six ions derived from the continents: sodium (Na+), potassium (K+), magnesium (Mg++), calcium (Ca+), chloride (Cl-), and sulfate (So4=).

        2. Increasing salinity causes sea water to become more dense if temperature is not changed. Salinity is increased by an excess of sea water evaporation over precipitation.