(WC) Convection, Conduction, and Radiation Lesson

Convection, Conduction, and Radiation

The sun serves as Earth's source of energy.

Energy is transferred between the earth's surface and the atmosphere in one of three ways. When energy is transferred from a hotter object to a cooler one it is referred to as heat.

• convection
• conduction
• radiation

Convection

Convection is the transfer of thermal energy through the movement of fluids (liquids or gases).

In the atmosphere, convection includes rising and sinking of air masses and smaller air parcels. These vertical motions effectively distribute heat and moisture throughout the atmospheric column and contribute to cloud and storm development (where rising motion occurs) and dissipation (where sinking motion occurs).

To understand the convection cells that distribute heat over the whole earth, let's consider a simplified, smooth earth with no land/sea interactions and a slow rotation. Under these conditions, the equator is warmed by the sun more than the poles. The warm, light air at the equator rises and spreads northward and southward, and the cool dense air at the poles sinks and spreads toward the equator. As a result, two convection cells are formed. 

The Earth's main energy source is the sun. The sun causes convection within the atmosphere, which in turn affects weather and climate.

 

Conduction

Conduction is the transfer of thermal energy that results from the collision of particles.

Let's imagine you have just baked a pan of chocolate chip cookies. Before pulling the cookies out of the oven you would want to have something to put between your hand and the hot cookie sheet. Using potholders or oven mitts will save your fingers and hand from being burned.

Some solids, such as metals, are good conductors of heat while others, such as wood, are poor conductors. The closer together molecules are in a substance, the more effectively the can conduct heat. Molecules that are heated have more energy. Molecules that are cold move slower and have less energy. The faster moving molecules are transferred into slower moving molecules.

Air is a poor conductor, most energy transfer by conduction occurs right at the earth's surface. At night, the ground cools and the cold ground conducts heat away from the adjacent air. During the day, solar radiation heats the ground, which heats the air next to it by conduction.

We have learned how the Earth's rotation results in the coriolis effect this rotation makes winds in the Northern Hemisphere curve to the right and winds in the Southern Hemisphere curve to the left.

Radiation

Radiation is the direct transfer of energy from the sun by electromagnetic waves. The shorter the wavelength the higher the energy associated with it.

Radiation can transmit heat through a vacuum. This is important because there is no air in space from which the sun's energy must travel through to energize our planet.

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