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Global Circulation

Learner Outcomes

By completing this activity, the learner will:

Exploration

Observe a current satellite image of the Earth. Sketch the locations of major horizontal cloud belts surrounding the Earth. Are there corresponding horizontal regions of no clouds? What are the major mega-geographical regions beneath the cloud belts and non-clouded regions?

Teacher-Centered Discussion

Part 1:

Observe these satellite images of the southern hemisphere.

Teacher Directed Questions:

Why are patterns more uniform in southern hemisphere than the northern hemisphere? Consider: topographical differences, energy budget differences, rotational differences.

Air flow demonstrates definite patterns over the surface of the earth. Latitudinal pattern of air flow in the southern hemisphere is more nearly perfect than that of the northern hemisphere.

Part 2:

Identify the components of the global circulation system as determined from an examination of a current, small scale satellite image such as the world-wide montage found at the Space Science and Engineering Center located on the University of Wisconsin-Madison campus.

Teacher Directed Questions:

Discuss their relationship to the global circulation system. What do you see at the ITCZ? Do you see the different pressure belts? (Polar High, Easterlies, etc.)

Part 3:

Look at the current GOES 8 or GOES 9 satellite images. Select several for a variety of views. Good IR images can be found The Weather Machine or at Unisys Weather site. World Weather Links has several satellite pictures.

Teacher Directed Questions:

Identify as many of the four uplift mechanisms as you can find evidence for. What is the evidence? What latitudes are associated with each?

Part 4:

Examine carefully the 500Mb chart, the surface map, and the IR satellite image for the January 12, 1996 storm, showing the development of a frontal system in the midlatitudes of North America. Make particular note of the relationships between the meanders (Rossby Waves) in the jet stream (visible on the upper level charts) and the positions of the surface lows and highs, and the surface fronts. Note also pressure, cloud pattern, and wind pattern associated with troughs and ridges; make some general predictions about conditions on the ground in the middle of a trough, in the middle of a ridge, and near the vertex of the trough. Discuss your results.

Teacher Directed Questions:

Discuss pressure, cloud patterns, and wind patterns. Students should download images and keep them in a portfolio with a discussion about the image.

Part 5:

Upper level atmospheric pressure maps can be found at the Boulder, Colorado Center for Atmospheric Research, Ohio State, or the University of Wyoming. Look at the current 200 Mb, 300 Mb, or 500 Mb pressure maps.

Teacher Directed Questions:

Determine by the contour line spacing where convergence aloft is likely to be happening and where divergence aloft is likely to be taking place. From this, predict the positions of the surface highs and lows. Compare your predictions to the actual positions of the highs and lows as shown on a surface pressure map. You can make a vector field of winds aloft, assuming geostrophic flow and that wind speed is inversely proportional to contour spacing, if one is not available. Each wind arrow in the vector field should be proportionate to the pressure gradient and parallel to the isobars; from this, you should be able to determine where convergence and divergence aloft are taking place.

Extensions

How do seasonal variations change the location of the ITCZ?

Points to Remember

  1. Latent heat storage and release is a major factor in the redistribution of energy on the surface of the earth.
  2. Vaporization of water from the surface of the ocean in areas of surplus solar energy is a major factor in the redistribution of water and energy on the surface of the earth.
  3. Release of latent heat is the major driving force behind storms of all kinds.
  4. The contrast in insolation between lower latitudes and higher latitudes is the main factor controlling pressure gradients which, in turn, control air movements.
  5. The global circulation system is determined by variations in insolation, combined with the Coriolis effect due to the earth's rotation.
  6. The global circulation system is a major controlling factor of the world's weather patterns.
  7. The world's weather patterns, averaged over a long period of time, produce the world's climatic patterns.
  8. Past, present, and future climate changes are a result in changes in the global circulation system, which in turn are caused by changes in insolation and/or redistribution of water and energy.