Chapter 17

The Atmosphere:Structure and Temperature

Section 17.2

Heating the Atmosphere

Heating the Atmosphere

Energy Transfer as Heat• Heat is the energy transferred from one object to

another because of a difference in their temperatures.

• Temperature is a measure of the average kinetic energy of the individual atoms or molecules in a substance.– Kinetic energy is the energy of motion.

• When energy is transferred to the gases in the air, those particles move faster and the air temperature increases.– Energy is always transferred from high energy to low

energy.

Heating the Atmosphere

Energy Transfer as Heat• There are three mechanisms of energy transfer as heat:

– Conduction– Convection– Radiation

• All three of these processes happen simultaneously in the atmosphere.1. Conduction is the transfer of heat through matter by molecular

activity (collisions of molecules).– Air is a poor conductor, and thus, conduction is only important

between Earth’s surface and the air directly in contact with the surface.

– Conduction is the least important mechanism of heat transfer

Heating the Atmosphere

Energy Transfer as Heat2. Convection is the transfer of heat by mass

movement or circulation within a substance.– Convection takes place in fluids (liquids and

gases) as well as in solids (i.e. the mantle).– Most of the heat acquired by radiation and

conduction in the lowest layer of the atmosphere is transferred by convective flow.

Question:Which of the following is NOT true about radiation?

A. Radiation cannot travel through a vacuum.B. The hottest radiating bodies produce the

shortest wavelengths.C. All objects emit radiant energy. D. Objects that absorb radiation well emit

radiation equally as well.

Heating the Atmosphere

Heating the Atmosphere

Energy Transfer as Heat• Electromagnetic Waves

– The sun emits light and heat as well as the ultraviolet rays that cause a suntan. These forms of energy are only part of a large array of energy emitted by the sun, called the electromagnetic spectrum.

Electromagnetic Spectrum

Visible Light consists of an Array of Colors

Question:The average kinetic energy of the atoms or molecules in a particular substance in known as

A. Temperature.B. Heat.C. Conduction.D. Convection.

Question:Because of convection, the warmest air in a room

A. Spreads out in all directions.B. Rises toward the ceiling.C. Transfers heat to the walls.D. Sinks toward the floor.

Heating the Atmosphere

Energy Transfer as Heat3. Radiation is the transfer of energy (heat) through space by

electromagnetic waves.• Radiation travels out in all directions and unlike conduction

and convection, it can travel through the vacuum of space.• Solar energy reaches Earth by radiation.• There are four laws governing radiation:

1. All objects, at any temperature, emit radiant energy.2. Hotter objects radiate more total energy per unit area than colder

objects do.3. The hottest radiating bodies produce the shortest wavelengths of

maximum radiation.4. Objects that are good absorbers of radiation are good emitters as

well.

Heating the Atmosphere

What Happens to Solar Radiation?• When radiation strikes an object, there are

usually three different results:1. Some energy is absorbed by the object.2. Substances such as water and air are

transparent to certain wavelengths of radiation.– These substances transmit radiant energy.

3. Some radiation may bounce off the object without being absorbed or transmitted.

Heating the Atmosphere

Question: Which of the following is an example of radiation?

A. A metal spoon becomes warm after being set in a pot of boiling water.

B. Warm water rises because it is less dense than cool water.

C. Pancake batter cooks quickly after being spooned onto a hot griddle.

D. Our atmosphere is constantly being heated by the sun.

Heating the Atmosphere

What Happens to Solar Radiation?• When radiation bounces off an object, it can be either

reflected or scattered.– Reflection: Occurs when light bounces off an object.

• Reflected light has the same intensity as the incident ray.– Scattering: Produces a larger number of weaker rays

that travel in different directions.• Light disperses both forward and backward, but most of

the energy is dispersed forward.• Accounts for the brightness and blue color of the sky.

• About 30% of the solar energy reaching the outer atmosphere is reflected back to space.

Heating the Atmosphere

Heating the Atmosphere

Absorption • About half of the solar radiation that is

absorbed at Earth’s surface arrives as scattered light.

• About 50% of the solar energy that strikes the top of the atmosphere reaches Earth’s surface and is absorbed.– Most of this energy is reradiated skyward.

• The atmosphere effectively absorbs the longer wavelengths emitted by Earth (water vapor and carbon dioxide are the major absorbers).

Heating the Atmosphere

Absorption• Without the absorbing gases, Earth would not

be suitable for humans and other life forms.• This important phenomenon is called the

greenhouse effect.

Question:The blue color of the sky is the result of

A. Conduction.B. Scattering.C. Reflection.D. Absorption.