Atmosphere
Chapter 17
17.1 Atmospheric Characteristics
Atmosphere: the gaseous layer that surrounds the
Earth
I. In the past, gases came from volcanic eruptions
A. Water vapor was a major component of
“outgassing”
B. Other gases included carbon dioxide,
hydrogen, sulfur dioxide, and diatomic
nitrogen
II. Composition of Atmosphere
A. Earth’s lower atmosphere is a mixture of many
different gases we call air.
B. Air is made of 4 main gases
1. 78.08% Nitrogen (N)
2. 20.95% Oxygen (O2)
3. 0.934% Argon (Ar)
4. 0.036% Carbon Dioxide (C02)
C. Air contains particulate matter
1. Dust and earth
2. Chemicals
3. Pollen
4. Soot
D. Air is the same worldwide, with local variation
(ex: H20 vapor)
III. The Structure of the Atmosphere
A. Temperature changes greatly at different
altitudes (heights)
B. The atmosphere is divide into layers based on
temperature differences, like the layers of the
ocean.
How many layers do you see here?
IV. Atmospheric Layers
A. Troposphere
1. The lowest layer, the one we live in.
2. 0 to 15km above Earth
3. Contains 80% of the atmosphere’s mass
4. Most water vapor and weather are located
here
5. Stops at tropopause
6. Jetstream is located just below tropopause
(where most planes fly)
7. Temperature decreases with altitude
B. Stratosphere
1. The second layer
2. 15 to 50 km high
3. Dry (no water vapor)
4. Stable (no weather)
5. Ozone layer is located near the top
a. form of oxygen gas (O3 instead of O2)
b. protects us from Sun’s UV rays
c. absorbs UV rays and releases them as
heat
6. Temperature increases with altitude in the
stratosphere
7. Stops at stratopause
C. Mesosphere
1. the third layer
2. 50 to 90 km
3. Temperature decreases with altitude as you
move away from the ozone layer
4. Stops at mesopause
D. Thermosphere
1. 4th layer
2. Located above the mesopause
3. 90 km and higher above the Earth
4. The least dense layer of the atmosphere.
5. Composed of layers of N2, O2, He, and
finally H that thins out into space.
6. Temperature increases with altitude
because of the intense solar radiation
7. Also called the ionosphere because the air
is highly ionized.
8. Aurora Borealis (The Northern Lights) occur
here.
Thermal structure of the atmosphere
V. Earth – Sun Relationships
A. Rotation:
1. the spinning of Earth around its axis
2. Earth completes 1 rotation every 24 hrs.
3. results in day and night
4. fastest at equator, slowest at poles
At the equator, 1 rotation equals 40,074 km per 24 hours (1690 km/hr).
Near the poles, 1 rotation equals nearly 0 km per 24 hours (0 km/hr),
because the poles are nearest to the axis!
B. Earth’s axis
1. Imaginary rod running through the Earth
from the north pole to the south pole.
2. Earth rotates around this rod
counterclockwise
3. The axis is tilted 23.5°
4. Points straight towards Polaris, the North
Star! (This is why Polaris appears at the
same place in the sky every single night of
the year!)
C. Earth’s Revolution
1. Revolution: one complete orbit of Earth
around the sun
2. 365.24 days, or 1 year
Remember, the Earth is tilted 23.5° on its axis. So, depending on
where the Earth is in its orbit, 1 hemisphere is always tilted
toward the sun, as the other is tilted away.
D. The Seasons
1. When northern hemisphere is tilted toward
the sun  Summer
a. more direct sunlight
b. warmer temps
c. longer days
d. Summer Solstice:
i. longest day of the year
ii. June 21-22
iii. sun is directly over the Tropic of
Cancer
2. When northern hemisphere is tilted away
from the sun  Winter
a. least direct sunlight
b. colder temps
c. shorter days
d. Winter Solstice:
i. shortest day of the year
ii. December 21-22
iii. sun is directly over the Tropic of
Capricorn
3. Equinox:
a. day and night are equal all over the world
b. 2 days out of the year
c. ½ way between the solstices
d. neither hemisphere tilts toward the sun
e. Sun is directly over the Equator
f. Vernal Equinox: March 21-22; beginning of
spring in the northern hemisphere
g. Autumnal Equinox: Sept. 22-23; beginning
of fall in the northern hemisphere
page 482, Figure 8 – Solstices and Equinoxes
17.2 Heat and the Atmosphere
I. Heat Energy
A. Radiation: the transfer of heat energy in the
form of light
1. In the form of electromagnetic waves
2. Visible light, UV rays, infrared, etc.
3. This is how heat energy from the sun
reaches Earth
B. Conduction:
1. The transfer of heat energy through touching
Ex: Touching a hot pan; walking barefoot on hot
sand
2. Occurs through the collisions of atoms or
molecules
C. Convection:
1. The transfer of heat energy in a gas or liquid
because of density difference
2. Hot things are less dense than cold things
Ex: The air above a fire is heated, rises, and
then heats the air above it
What type of transfer?
Coffee warming a cup?
Conduction
Steam rising from coffee?
Convection
Pan warmed on stove?
Conduction
Fire warming your face?
Radiation
II. Heat and temperature
A. Temperature measures how fast the molecules
of a substance are moving.
B. Boiling water has more movement than cold
water and a higher temperature
C. Heat measures the total energy contained in
the particles in a substance.
1. A large cup of coffee has more heat energy
than a small cup of coffee
2. Heat moves from high to low temperature
III. Insolation and the Atmosphere
A. Insolation: incoming solar radiation
B. Earth’s atmosphere receives only about 1/twobillionth of the sun’s rays
C. Global Heat Budget: shows the overall flow of
energy into and out of the system. (Fig 12)
1. 30% reflected back out to space
2. 20% absorbed by gases (CO2 and H2O) in
the atmosphere
3. 50% is absorbed by Earth’s surface or used
during photosynthesis (eventually radiated
back into space as heat)
Solar Radiation (page 486, Fig 12)
D. Greenhouse Effect
1. Greenhouse gases (CO2, H20, CH4) absorb
and re-radiate heat into atmosphere
2. Helps to keep Earth at a livable temp.
E. Global Warming
1. An increase in the average global temperature
due to rising levels of carbon dioxide in the
atmosphere.
2. Main causes: burning of fossil fuels and
deforestation
3. Effects:
a. rising sea levels due to melting polar ice
b. unstable weather conditions
c. frequent heat waves and droughts
d. relocation of crop lands
17.3 Local Temperature Variations
Key Concept : Insolation heats the Earth’s surface
unequally.
I. Time of Day
A. Warmest time = Afternoon
1. Earth absorbs most heat at noon
2. Earth re-radiates heat after noon
B. Coldest time = just after sunrise
1. Ground and atmosphere lose heat all night
2. Additional heat is lost from evaporation of
water at sunrise
II. Latitude
A. Warmest parts of Earth = near the equator
• The sun’s rays are most directly overhead all
year long.
B. Coldest parts of Earth = near the poles
• The sun’s rays are least directly overhead.
Relationship of sun angle and solar radiation received
on Earth
III. Time of Year
A. Warmest season = summer
1. Sun directly overhead all season
2. Days are longer
B. Coldest season = winter
1. Sun is further away and not directly
overhead
2. Days are shorter
Relationship of sun angle to the path of solar radiation
and seasons due to Earth’s tilt
IV. Cloud Cover
A. More clouds = colder days and warmer nights
1. Reflects insolation to space during day
2. Traps heat from Earth during night
B. Less clouds = warmer days and colder nights
1. Allows insolation to reach Earth
2. Allows Earth’s radiation to escape to space
C. Clouds reduce the daily temperature range
(max high to max low)
V. Type of Material
A. Water and land don’t heat the same
1. Water heats more slowly than land
2. Water cools more slowly than land
B. Color and texture also affect absorption
1. Dark colors warm faster than light colors
2. Rough textures warm faster than smooth
VI. Temperature Inversion…
A. occurs when surface air is cooler than the upper
air.
B. Prevents convection, no circulation occurs.
C. Traps pollutants near surface.
VII. World Distribution of Temperature
A. Map shows the effects of latitude on incoming
solar radiation.
B. Isotherms – lines that connect points of same
temperature
C. Shows East to West lateral banding
D. Trend is decreasing temperatures from
equator to poles
E. All measurements are for sea level.