1. Review Question 1
When is the subsolar point directly over 20°N latitude?
A) Never
B) Between the summer solstice and the fall equinox
C) Between the spring equinox and the summer solstice
D) B and C

2. Review Question 2 Why is Pluto no longer considered a planet?
A) Because it is square
B) Because it is a thermonuclear reactor
C) Because it shares its orbit with another planet
D) Because it is 3 billion light years from the sun

3. Chapter 3 Earth’s Modern Atmosphere
Geosystems 6e
An Introduction to Physical Geography
Robert W. Christopherson
Charles E. Thomsen

4. The Atmosphere
Atmosphere: an envelop of gaseous mixture (also containing suspended solid and liquid particles and clouds) that encircles a planet

5. Earth’s Modern Atmosphere
The atmosphere is absolutely essential for life on Earth
Earth’s atmosphere exists in a series of spheres or layers that grade into one another  
Composition, temperature, and function  

6. Atmospheric Profile  
Our atmosphere extends to roughly 32,000 km (20,000 mi) from surface
The top of the atmosphere has no clear boundary
Gravity holds our atmosphere in place
Top of Thermosphere is at 480 km (300 mi) = top of the principle atmosphere
Exosphere

7. Atmospheric Composition
Two broad regions:
Heterosphere – outer atmosphere
80 km (50 mi) outwards, to top of thermosphere
Layers of gases sorted by gravity
Homosphere – inner atmosphere
Surface to 80 km (50 mi)
Gases evenly blended
Ozone layer

8. Atmospheric Pressure
Figure 3.3

9. Atmospheric Temperature

10. Atmospheric Temperature
Troposphere
Surface to 18 km (11 mi)
90% mass of atmosphere
Normal lapse rate – average cooling at rate of 6.4 C °/ km (3.5 F°/1000 ft)
Tropopause

11. Temperature Profile
Figure 3.5

12. Atmospheric Temperature
Stratosphere
18 to 50 km (11 to 31 mi)
Temperatures increase with altitude
Ozone layer
Stratopause

13. Atmospheric Temperature
Mesosphere
Temperatures decrease with altitude
Mesopause

14. Atmospheric Temperature
Thermosphere
Roughly same as heterosphere
80 km (50 mi) outwards
Altitude of thermopause varies
Temperatures increase with altitude, but little actual heat

15. Atmospheric Function Ionosphere Ozonosphere
Absorbs cosmic rays, gamma rays, X-rays, some UV rays
Ozonosphere
Part of stratosphere
Ozone (O3) absorbs UV energy and converts it to heat energy

16. Protective Atmosphere
Figure 3.6

18. Four Principal Components of Atmosphere
Nitrogen from volcanic sources
Oxygen from photosynthesis
Argon through radioactive decay of isotopes
Carbon dioxide byproduct of life processes

19. Composition of the Atmosphere
Atmospheric gases
Permanent gases
Variable gases
Nitrogen (~78% of vol.)
Oxygen (~21% of vol.)
Argon (~1% of vol.) …
Water vapor (0-4% of vol.)
Carbon dioxide (0.037% of vol.)
Ozone ( % of vol.)
Methane ( % of vol.)
...

20. Water Vapor
The most abundant variable gas (0.25% of total atmospheric mass).
Added and removed from the atmosphere through the hydrologic cycle.
A major contributor to Earth’s energy balance and many important atmospheric processes.

21. Carbon Dioxide
A trace gas accounting for only 0.037% of the atmosphere.
Added to the atmosphere through biologic respiration and decay, volcanic eruptions, and natural and human-related combustion.
Removed from the atmosphere by photosynthesis (go to biosphere).
Anthropogenically related increases in recent decades have led to great concern with regard to global “greenhouse warming”.

22. The steady increase of atmospheric CO2.
Carbon Dioxide
The steady increase of atmospheric CO2.
Question: the seasonal variation?

23. Methane 1.7 ppm; increase 0.01 ppm/yr.
Released to the atmosphere through fossil fuel activities, livestock digestion, and agriculture cultivation (especially rice).
An extremely effective absorber of thermal radiation emitted by Earth’s surface; hence related in the warming of the atmosphere.

25. Carbon
Carbon Sequestration – removing carbon in the form of carbon dioxide from the atmosphere and storing it in the terrestrial biosphere
Carbon stored in biomass of plants
Soil organic carbon is carbon retained by the soil in humus form

26. The Carbon Cycle- source of atmospheric carbon dioxide
Human acitivities release 7.1 GtC/yr (gigatons of Carbon per year).
2 GtC/yr absorbed by oceans.
1.9 GtC unaccounted for.
3.2 GtC remain in atmosphere.

27. Carbon Banks
Carbon bank – program that enables organizations to keep track of a stock or supply of greenhouse gases in secure fashion for future use in the trading market