Download Chapter2StructureofAtmosphere

Chapter 2
Atmosphere: Origin, Composition
and Structure
Driving Question
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What is the composition and
structure of the atmosphere?
Key Terms
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Atmosphere – a thin envelope of gases that encircles
the earth and other particles (aerosols)
Weather – the state of the atmosphere at a specific
place and time
Meteorology – the study of the atmosphere and the
processes that cause weather
Climate – weather conditions at some place averaged
over a specific time period
Climatology – the study of the climate
Various Models
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Scientific Model – an approximate
representation of a real system (EarthAtmosphere System)
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Conceptual
Graphical – weather map
Physical
Numerical – run by computers (used to predict
weather)
All models simulate reality and are subject to
error
Primeval Atmosphere
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Initially Hydrogen and Helium
Outgassing – release of gases from rock via
volcanoes and meteorites
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Added CO2, N2, water vapor, Ar, among others
Photosynthesis converts CO2 to O2
Presence of O2 allowed ozone layer to form
Atmospheres of Venus and Mars are
predominately CO2
Modern Atmosphere
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Homosphere – lowest 80km of the
atmosphere where principal gas ratios
remain relatively constant
Heterosphere – above 80km where
concentrations of heavier gases
decrease more rapidly
Important Gases
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Nitrogen (N2) ~ 78%
Oxygen (O2) ~ 21%
Argon (Ar) ~ 1%
Greenhouse Gases – trace amounts but
important role on Earth
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Water Vapor (H2O) ~ 0-4%
Carbon Dioxide (CO2)
Ozone (O3)
Methane (CH4)
Aerosols
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Tiny solid and liquid particles suspended
in the atmosphere
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Wind erosion of soil
Ocean spray
Forest fires
Volcanic eruptions
Agricultural and industrial activities
Pollution
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Air Pollutant – gas or aerosol that at a
certain concentration adversely affects
organisms and the environment
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Natural pollutant: carbon monoxide
Non-natural pollutant: benzene
Primary – harmful immediately upon
emission into atmosphere (car exhaust)
Secondary – results of chemical reactions
between primary pollutants (smog)
Gases in the atmosphere
Monitoring the Atmosphere
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Surface Observations
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First done in 1800’s by Army Medical Corps - now run by the
National Weather Service (NWS)
Automated Surface Observing System (ASOS)
 About 1700 across the US
 Fully automated year round
NWS Cooperative Observer Network
 About 8000 across the US
 Monitored by volunteers with equipment supplied by NWS
Doppler Radar
 About 113 operated by the NWS
 Others operated by television stations, military, private
companies
Monitoring the Atmosphere
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Upper Air Observations
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Radiosonde – measuring device carried through the
atmosphere by a weather balloon
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Transmit data immediately
Balloons are launched simultaneously at 0000 and 1200 UTC
Data transmitted (temperature, pressure, dewpoint, wind) are
plotted on a chart creating a sounding
Dropwindsonde – same thing except dropped by an airplane
instead of launched by a balloon
Satellites
The atmosphere is
divided into several
different concentric
layers. This plot shows
the variation in average
air temperature with
height.
Layers of the Atmosphere
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Troposphere
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Layer at the surface
Layer where weather occurs (except some high
clouds)
About 6km high at the poles and 20km at the
equator
Temperature generally decreases with height
Tropopause – boundary between troposphere
and stratosphere (average height near 12km)
Layers of the Atmosphere
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Stratosphere
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About 40km thick (extends to an altitude near
50km)
Layer where airplanes fly (location of jet
stream)
Layer where ozone is present
Temperature generally increases with height
Stratopause – boundary between
stratosphere and mesosphere
Pressure decreases
exponentially with height.
This means that the
majority of the molecules
that make up the
atmosphere are in the
lower layers. About 50% of
the atmosphere's mass is
within 6km of the surface
and 99.9% is within 50km.
Layers of the Atmosphere
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Mesosphere
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Thermosphere
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Base is about 50km above the surface
Temperature again decreases with height
Coldest layer of the atmosphere
Extends to the mesopause which is about 80km above the
surface of the earth
Extremely thin air (particles range from 1-10km apart)
Increasing temperature because first particles to receive
sun’s energy
Estimated top is about 500km
Exosphere (outer space)
Ionosphere
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Base is about 70-80km above surface
Primarily located in the thermosphere
Home to a high concentration of ions
and electrons
Location of the Aurora Borealis