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 3 Earth’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

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 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

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

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 (0.000007% of vol.) Methane (0.00017% of vol.) ...

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 The steady increase of atmospheric CO2. 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