Review Question 1 In your own words, what is Geography? BAD answer: The science that studies the relationships between natural and cultural systems and the interdependence of the two over space and time These are not YOUR words!

Review Question 2 Why are sunspots darker than the rest of the sun? A) Because they are hotter than the surrounding surface B) Because they are cooler than the surrounding surface C) Because of solar wind D) Because there is no sunlight on them

Review Question 3 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 & C

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

The Atmosphere 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 Atmospheric Temperature

Temperature Profile Figure 3.5

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

Atmospheric Temperature Mesosphere Temperatures decrease with altitude Mesopause

Atmospheric Temperature Thermosphere Roughly same as heterosphere 80 km (50 mi) outwards Altitude 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 (O 3 ) 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 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.)...

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.  Anthropogenically related increases in recent decades have led to great concern with regard to global “greenhouse warming”.  Removed from the atmosphere by photosynthesis (go to biosphere).

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

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

Variable Atmospheric Components Natural Factors That Affect Air Pollution Winds – gather and move pollutants Landscape – mountains and hills can form barriers to air movement or can direct pollutants Temperature inversions – trap pollutants and do not allow them to be diluted by the atmosphere

Wildfires Figure 3.7

Temperature Inversion Figure 3.9

Pollution Sources Figure 3.10

Antarctic Ozone Hole Figure FS 3.1.1

Ozone Hole Ozone losses in the midlatitudes 6-8% per decade Alters atmospheric chemistry, biological systems, ocean phytoplankton, fisheries, crop yields, human eye and skin tissue, and human immunity Ozone hole is not caused by global warming

CFCs Synthetic molecules of chlorine, fluorine, and carbon Released by aerosol sprays, propellants, and refrigerants Do not break down naturally or dissolve in water

CFCs When CFCs reach the stratosphere, they are split by UV light The freed chlorine atom breaks apart ozone atoms creating ClO and O 2 O 2 is transparent to UV radiation

ClO and O 3 Figure FS 3.1.2