SIO 210: Introduction to Physical Oceanography

Atmospheric Circulation

Lynne Talley, Fall, 2016

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Reading


DPO: Chapter 5.8

Outline:

  • Temperature structure - troposphere, tropopause, stratosphere, mesosphere, thermosphere
  • Forcing: unequal distribution fo solar radiation
  • Wind: direct circulation - sea and land breeze, monsoon, Walker circulation
  • Hadley circulation
  • Jet stream
  • Large-scale wind patterns - westerlies, trades, pressure distributions
  • Wind stress: drag coefficient
  • Cloud cover
  • Precipitation and evaporation
  • Air-sea heat flux components. Shortwave, longwave, sensible, latent, total. Bulk parameterizations.

  • Figures from the NCEP/NCAR reanalysis project:
    Northern hemisphere long-term mean sea level pressure,
    Southern hemisphere long-term mean sea level pressure,

    Study problems

    1. Suppose you are riding along the winter jet stream in a high altitude balloon. How long would it take to circumnavigate the globe? Assume the stream is located at a latitude of 30 degrees and has mean velocity of 40 m/s. (Radius of earth = 6371 km)

    2. A lake 15 km long is initally at rest with no wind blowing on it. One day, a steady wind starts to blow along the axis of the lake at a rate of u_10 = 10 m/s. Calculate the wind stress. After several days, the lake comes into equilibrium with the wind stress. In steady state the wind stress is balanced by the hydrostatic pressure force of the elevated water at the downwind shoreline. What is the final difference in height of the water between the upwind and downwind ends of the lake? (Density of air = 1.3 kg/m3; Drag Coefficient from Stewart Fig. 4.6)

    Study questions

    1. At about what latitude in the northern hemisphere does the switch from trades to westerlies occur?

    2. What direction is the prevailing wind at the equator?

    3. If the wind speed at 10 meters height is 10 m/sec, what is the wind stress on the ocean? (use drag coefficients from lecture or from Stewart electronic notes)

    4. Is the Walker circulation in approximate geostrophic balance? Is the jet stream in approximate geostrophic balance?

    5.On the weather map of the U.S. used in the previous lecture (lecture 4), identify the high pressure regions and note for yourself which the geostrophic wind should go around the high.

    6. The North Atlantic atmospheric pressure is dominated by two large features - the Bermuda High and the Iceland Low. At about what latitude is the center of each of these? Same question for the high pressure center and the Aleutian Low in the North Pacific.


    Additional learning resources

    UCAR MetEd unit on climatology (lots about weather at the beginning, moving to larger scale) (Nice illustrated introduction, also includes ocean currents; for the interactive version, leave out the print.htm in the url.)

    Munn, T., Encyclopedia of Global Environmental Change (32 various pages):
    These articles are included in the scanned pdf:

    1. A. Persson: Atmospheric Motions, pp. 221-231 (part 1)
    2. P. Brimblecombe: Atmospheric Structure, pp. 243-244 - note that the figure is in error and has a hand-written correction (pp. 26-27 of the pdf)
    3. extra: E. Schneider: Hadley Circulation (28th page of pdf)
    4. extra: R. Bryson: Jet Stream (29th and 30th pages of pdf)
    5. extra: E. Schneider: Trade Winds (1 paragraph on 31st page of pdf)
    6. extra: E. Schneider: Walker circulation (32nd page of pdf)

    Excellent basic textbook for further reading: Wallace, J.M and P. V. Hobbs, 2006. Atmospheric Science: an Introductory Survey, Second Edition. Elsevier.

    Some interesting links:

    NCEP Reanalysis (source of figures of longterm mean sea level pressure used in lecture): http://www.cdc.noaa.gov/cdc/data.ncep.reanalysis.html
    Winds:

    NASA website for Winds http://winds.jpl.nasa.gov/

    Quikscat wind images http://airsea-www.jpl.nasa.gov/seaflux/quikscat/quikscat.html

    NASA JPL site for air-sea interaction and wind data http://airsea-www.jpl.nasa.gov


    SIO 210 HOME Oct. 19, 2016