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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. Review Question 2. Why is Pluto no longer considered a planet? A) Because it is square

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Review question 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

Review question 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

Chapter 3 earth s modern atmosphere

Chapter 3Earth’s Modern Atmosphere

Geosystems 6e

An Introduction to Physical Geography

Robert W. Christopherson

Charles E.Thomsen

The atmosphere
The Atmosphere

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

Earth s modern atmosphere
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 

Atmospheric profile
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

Atmospheric composition
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

Atmospheric pressure
Atmospheric Pressure

Figure 3.3

Atmospheric temperature1
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

Temperature profile
Temperature Profile

Figure 3.5

Atmospheric temperature2
Atmospheric Temperature

  • Stratosphere

    • 18 to 50 km (11 to 31 mi)

    • Temperatures increase with altitude

    • Ozone layer

    • Stratopause

Atmospheric temperature3
Atmospheric Temperature

  • Mesosphere

    • Temperatures decrease with altitude

    • Mesopause

Atmospheric temperature4
Atmospheric Temperature


  • Roughly same as heterosphere

  • 80 km (50 mi) outwards

  • Altitude of thermopause varies

  • Temperatures increase with altitude, but little actual heat

Atmospheric function
Atmospheric Function

  • Ionosphere

    • 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

Protective atmosphere
Protective Atmosphere

Figure 3.6

Four principal components of atmosphere
Four Principal Components of Atmosphere

  • Nitrogen from volcanic sources

  • Oxygen from photosynthesis

  • Argon through radioactive decay of isotopes

  • Carbon dioxide byproduct of life processes

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 (0.000007% of vol.)

Methane (0.00017% of vol.)


Composition of the Atmosphere

Atmospheric gases

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.

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”.

The steady increase of atmospheric CO2.

Carbon Dioxide

Question: the seasonal variation?


  • 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.


  • 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

The carbon cycle source of atmospheric carbon dioxide
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.

Carbon banks
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