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 Heat
2. 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 Heat
3. 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.
2.
3.
4.
All objects, at any temperature, emit radiant energy.
Hotter objects radiate more total energy per unit area than colder
objects do.
The hottest radiating bodies produce the shortest wavelengths of
maximum radiation.
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.