1. Earth’s Atmosphere:
A Brief Intro
(and Ocean Circulation Patterns)
Dr. Mark A. McGinley
Honors College and Department of
Biological Sciences
Texas Tech University

2. Atmosphere
• An atmosphere is a layer of gases that may
surround a material body of sufficient mass and
that is held in place by the gravity of the body.
• An atmosphere may be retained for a longer
duration, if the gravity is high and the
atmosphere's temperature is low.
• Some planets consist mainly of various gases, but
only their outer layer is their atmosphere
• Wikipedia

3. Earth’s Atmosphere

4. Earth’s Atmosphere
• The atmosphere of Earth is a layer
of gases surrounding the planet Earth that is
retained by Earth's gravity.
• The atmosphere becomes thinner and thinner
with increasing altitude, with no definite
boundary between the atmosphere and outer
space.

5. The Earth’s Atmosphere
– The atmosphere has a mass of about 5×1018 kg
• three quarters of which is within about 11 km (6.8 mi;
36,000 ft) of the surface.
– An altitude of 120 km (75 mi) is where
atmospheric effects become noticeable
during atmospheric reentry of spacecraft.
– The Kármán line, at 100 km (62 mi), also is often
regarded as the boundary between atmosphere
and outer space.

6. The Earth’s Atmosphere

7. The Layers of Earth’s Atmosphere
• We will talk about the layers of earth’s
atmosphere in more detail later on.
• The layer closest to the earth is known as the
troposphere
– We live in the troposphere
– Factors that affect climate and weather occur in
the troposphere

8. Composition of dry atmosphere, by volume[2]
ppmv: parts per million by volume (note: volume fraction is equal to mole fraction for ideal gas only, see volume
(thermodynamics))
Gas Volume
Nitrogen (N2) 780,840 ppmv (78.084%)
Oxygen (O2) 209,460 ppmv (20.946%)
Argon (Ar) 9,340 ppmv (0.9340%)
Carbon dioxide (CO2) 394.45 ppmv (0.039445%)
Neon (Ne) 18.18 ppmv (0.001818%)
Helium (He) 5.24 ppmv (0.000524%)
Methane (CH4) 1.79 ppmv (0.000179%)
Krypton (Kr) 1.14 ppmv (0.000114%)
Hydrogen (H2) 0.55 ppmv (0.000055%)
Nitrous oxide (N2O) 0.325 ppmv (0.0000325%)
Carbon monoxide (CO) 0.1 ppmv (0.00001%)
Xenon (Xe) 0.09 ppmv (9×10−6%) (0.000009%)
Ozone (O3) 0.0 to 0.07 ppmv (0 to 7×10−6%)
Nitrogen dioxide (NO2) 0.02 ppmv (2×10−6%) (0.000002%)
Iodine (I2) 0.01 ppmv (1×10−6%) (0.000001%)
Ammonia (NH3) trace
Not included in above dry atmosphere:
Water vapor (H2O) ~0.40% over full atmosphere, typically 1%-4% at surface

9. Gases of the Atmosphere
• Nitrogen gas is the most common gas in the
atmosphere
– N2
– Two atoms of Nitrogen held together by a triple
bond
• Second strongest bond in nature (I think)
• Thus, nitrogen gas is fairly non-reactive
– We are surrounded by Nitrogen, but we can not
use atmospheric nitrogen to help make proteins,
nucleic acids, etc.

10. Gases of the Atmosphere
• Oxygen gas is the second most common gas in
the atmosphere. O2
• Oxygen is required for aerobic respiration
– Break down sugar to release energy that can be used
by our bodies
• This process is much more efficient in the the presence of
oxygen
• O2 can be converted to O3 (ozone) in the
atmosphere
– We will talk about the importance of ozone later on

11. Gases of the Atmosphere
• Carbon dioxide (CO2)
• Terrestrial plants convert carbon dioxide into
sugar during the process of photosynthesis
– Energy stored in sugar is required to power most
life on earth
• Carbon dioxide is a “greenhouse gas”

12. Wind
• Wind can be defined simply as air in motion. This
motion can be in any direction, but in most cases
the horizontal component of wind flow greatly
exceeds the flow that occurs vertically.
• Wind develops as a result of spatial differences
in atmospheric pressure. Generally, these
differences occur because of uneven absorption
of solar radiation at the Earth's surface.

13. Wind

14. Unequal Distribution of Solar Energy
Across the Earth
• Solar radiation more
concentrated at the
equator than at the
poles
– Because of the curvature
of the earth
• Thus, warmer near the
equator than at the
poles

16. Effect of Increasing Temperature on
Gasses
• When gasses are heated the molecules start
to “move” more which results in a lower
density of gas molecules
– Fewer molecules per volume
• As the density decreases, the mass of the gas
decreases

17. Hot Air Rises
• As air warms its density decreases which
causes the warmer air to become lighter than
the cooler air surrounding it
• Thus, the more dense, cooler air replaces the
warmer, lighter air near the surface of the
ground
• HOT AIR RISES

18. Hadley Cells

19. Hadley Cells
• Warm air at the equator rises and is replaced
by cooler air moving from higher latitudes
– From North to South in Northern Hemisphere
– From South to North in the Southern Hemisphere
• As air rises it cools.
– In the Northern Hemisphere high altitude winds
blow from South to North
– In the Southern Hemisphere high altitude winds
blow from North to South

20. Hadley Cells
• As the air cools at
high altitudes it
becomes heavier
• Falls to the earth at
approximately 30o
latitude N and S

21. Importance of Hadley Cells
• Influence global wind patterns
• Also have profound effects of global patterns
of precipitation
– We will talk much more about this later on