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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 • 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 • 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 3Earth’s Modern Atmosphere Geosystems 6e An Introduction to Physical Geography Robert W. Christopherson Charles E.Thomsen
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 • 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 • 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 • 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 Figure 3.3
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 Figure 3.5
Atmospheric Temperature • Stratosphere • 18 to 50 km (11 to 31 mi) • Temperatures increase with altitude • Ozone layer • Stratopause
Atmospheric Temperature • Mesosphere • Temperatures decrease with altitude • Mesopause
Atmospheric Temperature Thermosphere • Roughly same as heterosphere • 80 km (50 mi) outwards • Altitude of thermopause varies • Temperatures increase with altitude, but little actual heat
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 Figure 3.6
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?
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.
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
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 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 • www.icbe.com