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 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.
Radiation is the transfer of energy between two objects by electromagnetic waves. Heat radiates from the ground into the lower 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.
Heat transfer by movement of heated materials is called convection. Heat that radiates from the ground initiates convection cells in the atmosphere (Figure below).
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.
- 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?
1. What is moving in conduction? What is moving in convection?
2. The poles experience 24 hours of daylight in their summer. Why do poles receive less solar radiation than the equator?
3. What drives atmospheric circulation?