Atmosphere Contents

5. General Circulation

Conclusion

The general circulation of the atmosphere refers to the average of wind patterns on a global scale, and is driven by unequal heating at the Earth's surface. Distinct characteristics of the general circulation are the Coriolis Force, jet streams, subtropical highs, horse latitudes, Hadley cells, doldrums, polar fronts, the Ferrel cell, weak polar cells and Rossby waves. These characteristics depend on latitude with the Coriolis Force influencing air masses at low latitudes, sub tropical highs, horse latitudes, polar fronts and Rossby waves at about 40-60°. Jet streams tend to form in the mid-latitudes but at altitudes of 10 to 15km. Weak polar cells which are similar to Hadley cells occur at high latitudes.

Question and answers

1. Describe the general circulation of the atmosphere.

question 1 answers

2. What is the Coriolis force?

question 2 answers

3. What are the characteristics of the general circulation at low-latitudes?

question 3 answers

4. What pressure is associated with cyclone areas?

question 4 answers

5. What are the primary circulation features of equatorial regions?

question 5 answers

6. Where do Rossby waves occur?

question 6 answers

7. Name the two jet streams

question 7 answers

8. How is El-Niño caused?

question 8 answers

9. When and by whom was El-Niño first recognised?

question 9 answers

10. What are the worldwide effects of El-Niño?

question 10 answers

Question 1 answer

The general circulation of the atmosphere is driven by an unequal heating at the Earth's surface. Tropical (0-30°) and subtropical (30-40°) latitudes receive more energy from the sun than is given off by outgoing terrestrial radiation. There is consequently a year-round energy transfer from low to high latitudes. The general circulation of the atmosphere can also strongly influence the precipitation of many areas as seen by the global cloud coverage.

Question 2 answer

The Coriolis force, associated with Earth's rotation, deflects all objects not at the equator, to the right of the direction of motion in the northern hemisphere and to the left in the southern hemisphere. This provides westerly winds, aloft in both hemispheres, that can produce jet streams.

Question 3 answer

Heating of the Earth is greatest over the equator. Air rises in this region, often condensing into huge cumulus clouds and thunderstorms, liberating an enormous amount of latent heat which makes the air more buoyant. As the air rises it reaches the tropopause which acts as a barrier. Consequently the air has to move laterally towards the poles.

Question 4 answer

Cyclones are areas of low pressure and anti-cyclones are areas of high pressure.

Question 5 answer

Equatorial regions:
- 'Hadley cell' - 0 to 30° N + S. Linked to the monsoon regions of the summer hemisphere.
- strong convective motion = 'Intertropical Convergence Zone' (ITCZ) or 'equatorial trough';
a broad zonal trough of low pressure where the Trade winds converge. Identified by equatorial belt
of cloud and precipitation.
- 'walker circulation' - east-west (zonal) flow, resulting in jet stream formation.
- 'sub-tropical highs' - warm dry air subsides towards the surface. Cloud free and consequently
associated with the world's desert region.
- the surface horizontal flow is known as the trade winds. These converge at the ITCZ.
- Usually the ITCZ is displaced into the summer hemisphere.
- Doldrums in the summer hemisphere; a band of light variable winds separating the two trade systems.
- 'horse latitudes' - light variable winds associated with the sub-tropical high pressure systems.

Question 6 answer

In mid-high latitudes (40-60°).

Question 7 answer

Polar front jet streams and subtropical jet streams.

Question 8 answer

The El-Niño Southern Oscillation (ENSO) is caused by the cyclic warming and cooling of the surface ocean of the central and eastern Pacific.

Question 9 answer

Fishermen off the coast of South America in the late 1800s first recognised El -Niño as abnormally warm water in the Pacific ocean after the beginning of the year.

Question 10 answer

Drought and wildfires in one part of the world, and torrential rains to other, normally dry, regions of the Earth, for example, the 1982 El-Niño event.