1. Chapter 10.1 Planetary Atmospheres

2. 10.1 Atmospheric Basics Our goals for learning What is an atmosphere?
How do you obtain an atmosphere?

3. What is an atmosphere?
An atmosphere is a layer of gas that surrounds a world

4. How do you obtain an atmosphere?
Gain volatiles by comet impacts
outgassing during differentiation
Ongoing outgassing by volcanoes

5. Keeping an Atmosphere Atmosphere is kept by the world’s gravity
Low mass (small) planets = low gravity
=almost no atm.
High mass (large) planets = high gravity
= thick atm.
Gravity and pressure
Air pressure depends on how much gas is there (i.e. The atmospheric thickness.)

6. Gravity and Atmospheric Pressure
The stronger the gravity, the more gas is held by the world and the greater the weight of atm. on a point

7. Earth’s Atmosphere About 10 km thick
Consists mostly of molecular nitrogen (78%) and oxygen (21%)

8. Atmospheric Pressure
Gas pressure depends on both density and temperature.
Adding air molecules increases the pressure in a balloon.
Heating the air also increases the pressure.

9. What do atmospheric properties vary with altitude?

10. Light’s Effects on Atmosphere
Ionization: Removal of an electron
Dissociation: Destruction of a molecule
Scattering: Change in photon’s direction
Absorption: Photon’s energy is absorbed

11. Temperatures and composition change
with
Height
giving structure
to an atmosphere

12. Earth’s Atmospheric Structure
Troposphere: lowest layer of Earth’s atmosphere
Temperature drops with altitude
Warmed by infrared light from surface and convection

13. Earth’s Atmospheric Structure
Stratosphere: Layer above the troposphere
Temperature rises with altitude
Warmed by absorption of ultraviolet sunlight in the Ozone layer

14. Earth’s Atmospheric Structure
Mesosphere: Layer above the stratosphere
Temperature decreases with altitude
Coldest layer of the atmosphere

15. Earth’s Atmospheric Structure
Thermosphere: Layer at about 100 km altitude
Temperature rises with altitude
X rays and ultraviolet light from the Sun heat and ionize gases

16. Earth’s Atmospheric Structure
Exosphere: Highest layer in which atmosphere gradually fades into space
Temperature rises with altitude; atoms can escape into space
Warmed by X rays and UV light

17. What have we learned? How do you obtain an atmosphere?
What is an atmosphere?
A layer of gas that surrounds a world
How do you obtain an atmosphere?
comet impacts.
outgassing by differentiation, volcanoes,
Why do atmospheric properties vary with altitude?
They depend on how atmospheric gases interact with sunlight at different altitudes.

18. Atmospheric Processes 1
Our goals for learning
What are the key processes?
How does a planet gain or lose atmospheric gases?
How does the greenhouse effect warm a planet?

19. Atmospheric Processes
Gaining and losing atmosphere
Gains: volcanic outgassing, impacts, evaporation.
Losses: gas escape,impacts,condensation,surface reactions
Greenhouse Effect
Infrared energy is re-radiated back to the ground by CO2
Atmospheric circulation (convection)
Convection cells move gas from equator to pole and back.
Coriolis Effect
Wind direction is deflected by the rotation rate of the world.

20. Atmospheric Gains

21. Atmospheric Losses

22. Greenhouse Effect

24. Air Movement and Flow

25. What have we learned?
There are 3 ways of adding to atmosphere and 4 ways of depleting it.
Gas molecules can transfer out to space or down to the ground.
How does the greenhouse effect warm a planet?
Atmospheric molecules allow visible sunlight to warm a planet’s surface but absorb infrared photons, trapping the heat.

26. Atmospheric Processes 2 Weather and Climate
Our goals for learning
What creates wind and weather?

27. Air Movement
Gas molecules move from high density to lower density

28. Atmospheric Pressure
Gas pressure depends on both density and temperature.
Adding air molecules increases the pressure in a balloon.
Heating the air also increases the pressure.
(molecules more energetic)

29. Atmospheric Circulation (convection)
Heated air rises at equator
Cooler air descends at poles
Maximum
Sun warming

30. Coriolis Effect

31. Coriolis effect deflects north-south winds into east-west winds

32. Coriolis Effect breaks up Global Circulation
On Earth the large circulation cell breaks up into 3 smaller ones, moving diagonally
Other worlds have more or fewer circulation cells depending on their rotation rate

33. Coriolis Effect Winds blow N or S Winds are diagonal Winds blow W or E
Venus
Earth
Mars
Jupiter, Saturn
Neptune, Uranus(?)

34. Total
Atmosphere
Circulation

35. Intense radiation at the equator warms the air
Air cools as it rises, moisture condenses and falls as rain
Warm air rises, collecting moisture
Lots of rain in the tropics!

36. some of the rising air flows north some of the rising air flows south
Rising air is now dry…
some of the rising air flows north
some of the rising air flows south
Dry air descends at around 30º N
…and at around
30º S
Deserts
Deserts
The descending air flows N and S

37. Circulation patterns repeat at 30-60º and 60-90º… Hadley cells
Dry
Wet
Hadley cells
Dry
Polar cells (60-90º)
Wet
Ferrell cells ( º)
Dry
These are called circulation cells – the basic units of
Vertical atmospheric circulation
Wet
Dry

38. (vertical circulation) (horizontal circulation,
Air rises and falls
in Hadley, Ferrel, and
Polar cells
(vertical circulation)
Circulation cells
explain global
distribution of
rainfall
Earth’s rotation
determines
wind direction
(horizontal circulation,
Coriolis force)

39. What have we learned? What creates wind and weather?
Atmospheric heating and Coriolis effect.
Solar warming creates convection cells.
The coriolis effect drags winds sideways and breaks up the cells
The faster a planet spins, the more E-W gas movement there is

40. Weather and Climate
Weather is the ever-varying combination of wind, clouds, temperature, and pressure
Local complexity of weather makes it difficult to predict
Climate is the long-term average of weather
Long-term stability of climate depends on global conditions and is more predictable

41. Factors that can Cause Long-Term Climate Change
Brightening of Sun
Changes in axis tilt
Changes in reflectivity
Changes in greenhouse gases

42. Changes in Greenhouse Gases
Increase in greenhouse gases leads to warming, while a decrease leads to cooling

43. Most major greenhouse gases are increasing
in atmospheric concentrations

44. Global Warming

45. Seasons
Our goals for learning
What creates the seasons on Earth?

46. For this reason, it’s warmer near the equator than at the poles.
Climatic Variation & Seasons on Earth
Uneven heating of Earth’s surface causes predictable latitudinal variation
in climate. Why? - Angle of incidence… equator vs. poles
North Pole
Equator
Earth
South Pole
Thus, radiation is more intense near the equator compared to the poles.
For this reason, it’s warmer near the equator than at the poles.

47. Uneven heating of Earth’s surface causes atmospheric circulation
Greater heating at equator than poles
1. sun’s rays hit more directly (perpendicular)
2. less atmosphere to penetrate
Therefore
1. Net gain of energy at equator
2. Net loss of energy at poles
Now let’s look at regional variations in Earth’s energy budget

48. What about seasons? Why do we have them?
Earth’s distance from the sun varies throughout the
year – doesn’t that cause the seasons?
Tilt!
Because of the tilt of Earth’s axis, the amount of radiation received by Northern and Southern Hemispheres varies seasonally
A. Northern Hemisphere has summer when it tilts toward the sun, winter when it tilts away
B. Southern Hemisphere has summer when it tilts toward the sun, winter when it tilts away

49. Earth’s Seasons Earth North Pole Equator South Pole
Tilt of the Earth’s axis towards or away from the sun creates the seasons
When the north pole tilts toward the sun, it gets more radiation – more warmth
during the summer
SUMMER (Northern Hemisphere)
North Pole
Equator
Earth
When the north pole tilts toward the sun, the south pole tilts away
So when it’s summer in the north,
it’s winter in the south
South Pole
WINTER (Southern Hemisphere)

50. Earth’s Seasons Earth North Pole Equator South Pole
Tilt of the Earth’s axis towards or away from the sun creates the seasons
When the north pole tilts toward the sun, it gets more radiation – more warmth
during the summer
North Pole
WINTER (Northern Hemisphere)
Equator
Earth
When the north pole tilts toward the sun, the south pole tilts away
So when it’s summer in the north,
it’s winter in the south
South Pole
SUMMER (Southern Hemisphere)

52. Earth North Pole Equator South Pole Earth’s Seasons
Tilt of the Earth’s axis towards or away from the sun creates the seasons
WINTER (Northern Hemisphere)
When the north pole tilts away
from the sun, it gets less radiation –
So it’s colder during the winter
North Pole
Equator
Earth
South Pole
When the north pole tilts away from the sun, the south pole tilts toward it…
When it’s winter in the north,
it’s summer in the south
SUMMER (Southern Hemisphere)