Page 103 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 3 earth’s Modern atmosphere 67
Atmospheric Composition
Heterosphere
Atmospheric Temperature
Thermopause
Atmospheric Function
Ionosphere
Auroras
Ozone
layer Ozonosphere
Kittinger balloon
Mount Everest
Exosphere
480 400
320
200 160
80
50
20 10
0
Mark Lee
Distinct layers
of gases
Hydrogen Helium
Oxygen Nitrogen
Thermosphere
Mesopause
Mesosphere
Stratopause
Stratosphere
Equatorial tropopause
Polar tropopause
Troposphere
Homosphere
Blend of gases (see Table 3.1)
▲Figure 3.1 Profile of the modern atmosphere. note the small astronaut and balloon showing the altitude achieved by astronaut Mark lee and by Joseph kittinger, discussed in Geosystems Now.
countries, normal air pressure is expressed as 101.32 kPa (kilopascal; 1 kPa = 10 mb). (See Chapter 6 for further discussion.)
Atmospheric Composition Criterion
By the criterion of chemical composition, the atmo- sphere divides into two broad regions (Figure 3.1), the heterosphere (80 to 480 km altitude) and the homosphere (Earth’s surface to 80 km altitude).
Heterosphere The heterosphere is the outer atmo- sphere in terms of composition. It begins at about 80 km altitude and extends outward to the exosphere and inter- planetary space. Less than 0.001% of the atmosphere’s mass is in this rarefied heterosphere. The International
Space Station (ISS) orbits in the middle to upper hetero- sphere (note the ISS altitude in Figure 3.1).
As the prefix hetero- implies, this region is not uniform—its gases are not evenly mixed. Gases in the heterosphere occur in distinct layers sorted by gravity ac- cording to their atomic weight, with the lightest elements (hydrogen and helium) at the margins of outer space and the heavier elements (oxygen and nitrogen) dominant in the lower heterosphere. This distribution is quite differ- ent from the blended gases we breathe in the homosphere, near Earth’s surface.
Homosphere Below the heterosphere is the homo- sphere, extending from an altitude of 80 km to Earth’s surface. Even though the atmosphere rapidly changes density in the homosphere—increasing pressure toward
Georeport 3.2 Outside the Airplane
next time you are in an airplane, think about the air pressure outside. Few people are aware that in routine air travel they are sitting above 80% of the total atmospheric volume and that the air pressure at that altitude is only about 10% of surface
air pressure. Only 20% of the atmospheric mass is above you. if your plane is at about 11 000 m, think of the men who jumped from stratospheric heights, described in Geosystems Now; Felix Baumgartner started another 28 km higher in altitude than your plane!
Kilometres