Chapter 2: Atmosphere: Origin, Composition, and
Structure
Key Terms
• 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
Computer Forecast Models
• Scientific Model – an approximate representation
of a real system (Earth-Atmosphere 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. More at:
http://www.crh.noaa.gov/news/display_cmsstory
.php?wfo=lmk&storyid=106486&source=0
Modern Atmosphere
• 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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•
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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
• Tiny solid and liquid particles suspended in the
atmosphere
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Wind erosion of soil
Ocean spray
Forest fires
Volcanic eruptions (Reflect sunlight) (Mt. Pinatubo,
1993) http://scied.ucar.edu/shortcontent/mounttambora-and-year-without-summer
– Agricultural and industrial activities (Absorb
sunlight)
Pollution
• Air Pollutant – gas or aerosol that at a certain
concentration adversely affects organisms and the
environment
– 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 - air that has
restricted visibility due to pollution)(Red alert in
China, December 2015).
http://www.bbc.com/news/world-asia-china-35173709
Monitoring the Atmosphere
• Surface Observations
– 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
• Surface observations, continued
– Army monitored weather to compare with troop health
– Mid-1800s – national network of volunteer observers
– 1849 – telegraph companies transmitted weather conditions
free of charge
– 1860s – loss of ships in Great Lakes
• Government took a greater role in forecasting
– 1870 – President Ulysses S. Grant established 24 stations
under the auspices of the U.S. Army Signal Corps
– 1891 – transferred from military to civilian hands
• New weather bureau under U.S. Department of
Agriculture
Monitoring the Atmosphere
• Surface observations, continued
– Transferred to Commerce Department in 1940
– 1965, Weather Bureau reorganized into the National
Weather Service (NWS)
• Under Environmental Science Services Administration
(ESSA), which became National Oceanic and Atmospheric
Administration (NOAA)
– 1990s – NWS modernized and expanded
• Today,123 NWS Forecast Offices (see next slide)
• Added Automated Surface Observing Systems (ASOS)
NWS Forecast Offices
Monitoring the Atmosphere
Cooperative Observer Network
Automated Surface
Observing System
(ASOS)
– Member stations record daily
precipitation and max/min
temperatures for hydrologic,
agricultural, and climatic purposes
Monitoring the Atmosphere
• Upper Air Observations
– Radiosonde – measuring device carried through the atmosphere
by a weather balloon
• 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
Monitoring the Atmosphere
Launching a
Radiosonde
Radiosonde
Upper Air Observations
Locations of radiosonde
observation stations
Data from radiosonde
shown in a Stüve
diagram
Remote Sensing
• Measurement of
environmental
conditions by
processing signals that
are either emitted by an
object or reflected back
to a signal source
– Radar
– Satellites
Atmospheric Setup
The atmosphere is
divided into several
different concentric
layers. This plot shows
the variation in average
air temperature with
height.
Characteristics of Air Masses & Fronts
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
• 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 due to
sunlight heating the Earth’s surface and warms air above it.
– Tropopause – boundary between troposphere and
stratosphere (average height near 12km)
– Tropopause varies in height across the globe.
Layers of the Atmosphere
• Stratosphere
– 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
(Ozone absorbing solar radiation followed by a
release of energy, which warms the stratosphere)
– Stratopause – boundary between stratosphere
and mesosphere
Why do I want to fly here?
• Get to places faster
• It’s a fairly stable layer (most weather occurs in the
troposphere), less turbulence
Layers of the Atmosphere
• Mesosphere
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Base is about 50km above the surface
Temperature again decreases with height
Coldest layer of the atmosphere (little ozone)
Atmospheric pressure at around 1 mb
99% of atmospheric mass located below
Without proper breathing equipment, brain would become oxygen starved
Extends to the mesopause which is about 80km (50 miles) above the surface of
the earth
• Thermosphere
– Extremely thin air (particles range from 1-10km apart)
– Increasing temperature because first particles to receive sun’s energy (solar
radiation)
– Estimated top is about 500km
– May be 10 km between molecules
– Heat shield
• Exosphere (outer space)
Ionosphere
• Primarily located in the thermosphere
• Home to a high concentration of ions and
electrons
• Location of the Aurora Borealis
• Caused by the solar wind, in which Earth’s
magnetic field deflects
The Ionosphere and the Aurora
• The magnetosphere is caused by the deflection of the solar wind
by Earth’s magnetic field
• Solar wind = Stream of charged particles let go from the upper
atmosphere of the sun
Aurora borealis
Review
Air Temperature
and Altitudinal
Relationships in
the Atmosphere