What could cause such a spectacular, swirling funnel of air?
For many people, this sight is unfamiliar. It is a tornado. Tornadoes happen when heat is rapidly transferred between layers in the atmosphere.
Heat Transfer in the Atmosphere
Heat moves in the atmosphere the same way it moves through the solid Earth or another medium. What follows is a review of the way heat flows, but applied to the atmosphere.
In conduction, heat moves from areas of more heat to areas of less heat by direct contact. Warmer molecules vibrate rapidly and collide with other nearby molecules, transferring their energy. In the atmosphere, conduction is more effective at lower altitudes, where air density is higher. This transfers heat upward to where the molecules are spread further apart or transfers heat laterally from a warmer to a cooler spot, where the molecules are moving less vigorously.
Thermal convection where the heat source is at the bottom and there is a ceiling at the top.
What Drives Atmospheric Circulation?
Different parts of the Earth receive different amounts of solar radiation. Which part of the planet receives the most solar radiation? The Sun's rays strike the surface most directly at the equator.
The difference in solar energy received at different latitudes drives atmospheric circulation.
Air moving between large high and low pressure systems at the bases of the three major convection cells creates the global wind belts. These planet-wide air circulation systems profoundly affect regional climate. Smaller pressure systems create localized winds that affect the weather and climate of a local area.
An online guide to air pressure and winds from the University of Illinois is found here: http://ww2010.atmos.uiuc.edu/%28Gh%29/guides/mtr/fw/home.rxml.
- In conduction, substances must be in direct contact as heat moves from areas of more heat to areas of less heat.
- In convection, materials move depending on their heat relative to nearby materials.
- The equator receives more solar energy than other latitudes.
Use this resource to answer the questions that follow.
1. What powers our weather?
2. What does heat cause?
3. How does the tilt of the Earth affect heating?
4. What causes wind?
5. What occurs in the water?
6. What drives atmospheric circulation?