GEO 200: Physical Geography
Introduction to the Atmosphere
The Atmosphere
• The Earth is unique because of the composition of
its atmosphere, which makes life possible.
– It supplies the oxygen that all but a handful of
organisms need to survive.
– It supplies the carbon dioxide that photosynthetic plants
and animals use to make the carbon-based compounds
required for living things.
– It maintains the water supply for life.
– It moderates the climate against temperature extremes.
– It protects Earth from the Sun’s ultraviolet radiation.
Air
• Air is synonymous with atmosphere, and is a
mixture of gases, mainly nitrogen and oxygen.
– Also contains varying quantities of liquid and solid
particles, such as soot.
• Air is typically invisible: colorless, odorless, and
tasteless.
– Gaseous impurities can be smelled.
– Suspended materials can be seen if in great enough
concentration, such as water vapor in clouds.
Vast ocean of air
• The atmosphere completely surrounds Earth, like
an ocean with land and water at its bottom.
• It is held close to the surface by gravity, but
because the strength of the attraction is low, the
atmosphere is capable of vast, rapid motions.
• The atmosphere interacts with other components
of the Earth’s environment.
Extent of atmosphere, part 1
• The atmosphere extends outward to 10,000
kilometers.
• Most of its mass is concentrated at low elevations.
– More than half of the atmosphere’s mass is below the
elevation of the peak of Mount McKinley (6.2
kilometers).
– More than 98 percent of the atmosphere’s mass lies
within 26 kilometers of sea level.
• Atmosphere fills empty spaces in rocks and soil,
such as caves and crevices.
Extent of atmosphere, part 2
• Gases are dissolved in the waters of the Earth as
well as in the bodily and cellular fluids of living
organisms.
Gases of the Atmosphere
• Basic composition of the atmosphere:
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Nitrogen – 78%
Oxygen – 21%
Argon – nearly 1%
Neon, helium, methane, krypton, hydrogen, water
vapor, carbon dioxide, ozone, carbon monoxide, sulfur
dioxide, nitrogen oxides, and various hydrocarbons –
trace amounts
H20, CO2, and climate, part 1
• Only water (H20) vapor and carbon dioxide (CO2)
have a significant effect on weather and climate.
– Water vapor determines the humidity of the
atmosphere, is the source of all clouds and
precipitation, and is intimately involved in the storage,
movement, and release of heat energy.
– Water vapor and atmospheric CO2 significantly affect
the climate because they can absorb infrared radiation,
keeping the lower atmosphere warm.
• The proportion of CO2 has been increasing at about 2 parts per
million (ppm) per year and is at present about 370 ppm.
H20, CO2, and climate, part 2
• It is debatable what exact effects this increase in
atmospheric CO2 is having/will have on
atmosphere, but most scientists believe it will
make the lower atmosphere warm up enough to
cause major global climatic changes.
Ozone and other gases
• Ozone is a molecule made up of three oxygen
atoms (O3). It is concentrated in the ozone layer,
where it helps to absorb deadly ultraviolet solar
radiation and protect animal life.
• The proportion of carbon monoxide, sulfur
dioxide, nitrogen oxides, and various
hydrocarbons is also increasing because of
emissions from factories and cars.
– All are hazardous to life and may have an effect on
climate.
Particulates, part 1
• Particulates are solid and liquid particles found in
the atmosphere
• They can be visible and/or invisible.
• They come from both natural and human-made
sources.
– Larger particles are mainly water and ice.
Particulates, part 2
• Particulates affect the weather and climate in two
ways:
– Many are hygroscopic (they absorb water), and water
vapor collects around them, which contributes to cloud
formation;
– Particulates can either absorb or reflect sunlight, thus
decreasing the amount of solar energy that reaches
Earth’s surface.
Vertical structure
• Trailing bits first:
– “–sphere” is used when talking about the entire layer;
– When referring to just the upper portion of a layer or
the boundary between two layers, “-pause” is used.
• One way to define layers in the atmosphere is on
the bases of temperature trends. There are five
thermal layers in the atmosphere: troposphere.
stratosphere, mesosphere, thermosphere, and
exosphere.
Thermal layers, part 1
• Temperature alternately decreases and increases
from one layer to the next.
• The thermal layers:
– The troposphere is the lowest thermal layer of the
atmosphere, in which temperature decreases with
height. Most weather phenomena occur in the
troposphere.
• Height of the troposphere varies with time and place.
– The tropopause is a transition zone at the top of the
troposphere, where temperature ceases to decrease with
height.
Thermal layers, part 2
• The thermal layers (continued):
– The stratosphere is the atmospheric layer directly above
troposphere, where temperature increases with height.
– The stratopause is the top of the stratosphere, elevation
about 48 kilometers, were maximum temperature is
reached.
– The mesosphere is the atmospheric layer above the
stratopause, where temperature again decreases with
height as it did in the troposphere (note, this term also
refers to the rigid part of the deep mantle, below the
asthenosphere).
Thermal layers, part 3
• The thermal layers (continued):
– The mesopause is transition zone at the top of the
mesosphere.
– The thermosphere is the highest recognized thermal
layer in the atmosphere, above the mesopause, where
temperature remains relatively uniform for several
kilometers and then increases continually with height.
– The exosphere is the highest zone of Earth’s
atmosphere.
Thermal layers, part 4
• The warm zones of the thermal layers each have
their own specific source of heat.
– In the troposphere, it’s the visible portion of sunlight.
– In the stratosphere and thermosphere, the Sun’s
ultraviolet rays serve as the heat source (the warm zone
of the stratosphere is near the top of the ozone layer,
which absorbs UV rays).
Atmospheric pressure
• Atmospheric pressure is basically the weight of
overlying air. Thus air pressure is normally highest
at sea level and rapidly decreases with altitude.
– One-half of all gas molecules making up the
atmosphere are below 5.6 km, and 90 percent are below
16 km.
– Above 80 km, atmospheric pressure is so slight that it
cannot register on an ordinary barometer.
Composition layers, part 1
• Principal gases of atmosphere have a uniform
vertical distribution in the lowest 80 km.
• The homosphere is the zone of homogeneous
composition; in both troposphere and stratosphere.
• The heterosphere is the zone of heterogeneous
composition; begins in mesosphere and continues
through exosphere; where gases tend to be layered
according to their molecular masses rather than
having the homogenous composition of the
homosphere.
Composition layers, part 2
• The ozonosphere is the ozone layer; the zone of
relatively rich concentration of ozone in the
atmosphere, between about 15 to 48 km high, that
absorbs ultraviolet radiation.
• The ionosphere is the deep layer of ions,
electrically charged molecules and atoms, in
mesosphere (middle and upper parts) and
thermosphere (lower part) that aids in longdistance communication by reflecting radio waves
back to Earth. Also generates auroral displays.
Composition layers, part 2
• The ozonosphere is the ozone layer; the zone of
relatively rich concentration of ozone in the
atmosphere, between about 15 to 48 km high, that
absorbs ultraviolet radiation.
• The ionosphere is the deep layer of ions,
electrically charged molecules and atoms, in
mesosphere (middle and upper parts) and
thermosphere (lower part) that aids in longdistance communication by reflecting radio waves
back to Earth. Also generates auroral displays.
Atmospheric change
• Pollutants, inefficient and wasteful fossil fuel use,
and rapid population growth are all contributing to
changes in Earth’s atmosphere, as found by report
of the World Conference on the Changing
Atmosphere Implications for Global Security in
1988.
• Report also predicted that we could expect severe
economic and social dislocation because of these
changes.
Ozone depletion, part 1
• Ozone is naturally produced in the stratosphere
and it serves to protect life on Earth by shielding it
from the deadly ultraviolet rays of the Sun.
– It is created in the upper atmosphere by the action of
UV radiation.
– UV-C radiation splits oxygen molecules into free
oxygen atoms which then combine with oxygen
molecules to form ozone.
– In the stratosphere ozone molecules will be naturally
broken down into oxygen molecules and free oxygen
atoms by UV-B and UV-C radiation.
Ozone depletion, part 2
• Ozone is naturally produced (continued).
– The breakdown and formation of ozone is an ongoing
process in this layer of the Earth’s atmosphere.
• When produced in the troposphere, ozone harms
life, where it damages tissues in humans (eyes,
lungs, noses); it also damages vegetation and
corrodes buildings.
– Ozone is produced naturally in the stratosphere, while
the combination of human activity such as automobile
emissions and incoming solar radiation leads to its
production in the troposphere.
Ozone depletion, part 3
• When produced in the troposphere, ozone harms
life (continued).
– Depletion of stratospheric ozone increases the amount
of tropospheric ozone.
• Ozone in the stratosphere, lying in the ozone layer,
is being depleted through a combination of natural
and human-produced factors.
– The natural include the oscillation of the stratospheric
winds that occurs every 2.3 years, the 11-year sunspot
cycle, volcanic debris from eruptions, and El Niño,
which occurs every 3 to 5 years.
Ozone depletion, part 4
• Ozone in the stratosphere . . . is being depleted
(continued)
– Chlorofluorocarbons (CFCs) are synthetic chemicals
that affect ozone layer.
• When ultraviolet radiation breaks down CFCs in the
ozonosphere, the released chlorine then breaks down the ozone
molecules, creating chlorine monoxide and oxygen molecules,
which cannot filter solar radiation.
Ozone Depletion
Ozone depletion, part 5
• The ozone layer has been getting thinner since the
1960s, when CFCs came into major use as
refrigeration and cooling agents. Then in 1979, a
“hole” in ozone layer developed over Antarctica.
Although it ebbs and flows each year, it has been
increasing in size and duration each year. Then in
1980s, a similar “hole” developed over Arctic.
Ozone depletion, part 6
• In 1978, many countries began banning use of
CFCs, and by 1996, all countries of the industrial
world had banned them.
– Developing nations have an extended deadline of 2010
before they must ban them.
• It is estimated that the current reservoir of CFCs in
the atmosphere will persist for 50 to 100 years,
continuing to deplete stratospheric ozone long
after they are no longer produced or used.
– Most research has predicted that the hole will not
recover until sometime between 2040 and 2050.
Weather vs. climate
• Weather refers to short-run atmospheric conditions
that exist for a given time in a specific area.
• Climate refers to the pattern or aggregate of dayto-day weather conditions over a long period of
days, encompassing both the average
characteristics and the variations and extremes.
Elements of weather/climate
• There are four main elements, or variables, of
weather and climate:
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Temperature
Pressure
Wind
Moisture
• All are measurable, vary frequently (if not continuously) in
time and space, and provide the key to deciphering the
complex mechanisms and process to weather and climate.
Controls of weather/climate
• There are seven principal controls that cause or
influence the elements of weather and climate:
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Latitude
Distribution of land and water
General circulation of the atmosphere
General circulation of the oceans
Elevations
Topographic barriers
Storms
Latitude
• Constantly changing positional relationship
between Sun and Earth results in continuously
changing amounts of solar energy that reach any
given point on the surface of the Earth.
• As a result, the basic distribution of heat energy
over the surface of the Earth is a function of
latitude.
– Control latitude influences element temperature.
Distribution of land and water
• One of the most fundamental climatic differences
is that between continental and maritime climates.
– Oceans heat and cool more slowly and to a lesser extent
than land masses, thus maritime climates experience
milder temperatures than continental areas at similar
latitudes.
• Average January temperatures in Seattle, Wash., and Fargo,
N.D., differ by as much as 18 degrees C., with Seattle’s
average being 5 degrees C and Fargo’s being -13 degrees C.
– Oceans also prolific source of atmospheric moisture,
thus maritime climates more humid than continental
climates.
Circulation of the atmosphere
• Atmosphere is in constant motion.
– Flows range from transient breezes to regional wind
patterns.
– Semipermanent patterns of major wind and pressure
patterns greatly influences most elements of weather
and climate.
• Simplifying the actual circulation shows that general surface
wind direction varies according to latitude, with most surfaces
winds in tropics coming from east, while those in middle
latitudes flow mostly from the west.
Circulation of the ocean
• Movements of the oceans are analogous to
motions of the atmosphere.
• Motions range from minor ones to semipermanent
currents affecting entire ocean basins.
– For example, eastern coasts of continents have warmer
currents while western coasts have cool currents.
• Currents move warm water toward poles and cool
water toward equator.
• Ocean currents likewise affect climate.
Elevation
• Temperature, pressure, and moisture content
generally decrease with elevation (altitude).
• Decrease in these factors with elevation has
significant effects on weather and climate,
especially in mountain regions.
Topographic barriers
• Mountains and large hills can affect weather and
climate by diverting wind flow and interrupting
flow of moisture.
• The windward side of a mountain range (the side
facing the wind) often has a very different climate
from the leeward side (the side sheltered from the
wind).
– This typically has a major effect on moisture and
average rainfall, with one side being very wet and the
other very dry.
Storms
• Storms result from interaction of the other climate
controls, but then create their own specialized
weather circumstances like other controls.
– Some types of storms are predominant enough and
frequent enough to affect climate as well as weather.