Global Atmospheric Circulation- An Introduction

Atmospheric circulation is the large-scale movement of air by which heat is distributed on the surface of the Earth. Solar energy powers the atmospheric system and the energy circulations within it. The amount of solar energy (heat budget) received varies with latitude.  The tropics have an energy surplus as they gain more from insolation than is lost by radiation.  But the higher temperate and polar latitudes have an energy deficiency losing more by radiation than is gained by insolation

This disparity in the earth’s heat budget is counteracted by the ocean currents which accounts for 40% of the redistribution and atmospheric circulation accounting for 60% respectively.

This is achieved through three main convection cells:

1) Hadley Cell (Tropical Cell) 

2) Ferrel Cell (Mid-latitude Cell)

3) Polar Cell

While the Hadley, Ferrel, and Polar cells are major players in global heat transport, they do not act alone. Disparities in temperature also drive a set of longitudinal circulation cells, and the overall atmospheric motion is known as the zonal overturning circulation.
 
As the Coriolis force runs across the 3 convection cells it causes the deflection of the wind creating some main patterns:

1) Easterlies
2) Doldrums
3) Westerlies
4) Horse Latitudes
5) Polar Easterlies
6) Polar front

This post is going to focus on the Hadley cell as this is said to have most impact on the atmospheric circulation.

The Hadley cell is a three dimensional atmospheric circulation cell located at roughly 0 to 30° North and South of the equator. Low latitude air moves towards the Equator and heats up.  As it heats it rises vertically and moves polewards in the upper atmosphere. This forms a convection cell that dominates tropical and sub-tropical climates.

As mentioned previously in this post near the poles, heat is lost to space by radiation exceeds the heat gained from sunlight, so air near the poles is losing heat. Conversely, heat gained from sunlight near the equator exceeds heat losses, so air near the equator is gaining heat. Air rises near the equator, flows north and south away from the equator at high altitudes, sinks near the poles, and flows back along the surface from both poles to the equator.

The combination of these two processes sets up a general circulation pattern: air rises near the equator, flows north and south away from the equator at high altitudes, sinks near the poles, and flows back along the surface from both poles to the equator. The video above just demonstrates the Hadley cell circulation in more detail and summaries all of the above.

http://www.youtube.com/watch?v=DHrapzHPCSA

Classroom task

I would like to do a summary of the Hadley cell circulation. I would like the students to chose how they would do this but the requirements would include at least 6 bullet points of how the circulation works. Other tasks could include true/false statements about the Hadley cell also getting in the diagram and filling in the stages of the circulation cell.

Next post will be explaining the other two cells; Polar and Ferrel in more detail and also beginning to explain the major wind patterns.