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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 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
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
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