1. AMS Weather Studies Introduction to Atmospheric Science, 5th Edition
Chapter 2
Atmosphere: Origin, Composition, & Structure
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2. Driving Question
What is the composition and structure of the atmosphere?
This chapter covers:
Evolution of the atmosphere
Investigation of the atmosphere
How meteorologists monitor the atmosphere
Surface and upper-air observations and remote sensing
The temperature profile of the atmosphere
Electromagnetic characteristics of the upper atmosphere
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3. Atmosphere viewed from space
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4. Case-in-Point African Origins of Wind-Borne Dust in the Americas
Weather and climatic issues in one part of the world can affect those in another part.
North African dust storms can affect the weather and air quality of the southeastern U.S.
Dust can harbor microscopic disease-causing organisms.
This dust may be harming coral reefs in the Caribbean.
This dust may increase the frequency of red tides.
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5. Evolution of the Atmosphere
Earth System
Made up of atmosphere, hydrosphere, geopshere, biosphere
Atmosphere
Composed of gases and suspended particles
Half of mass found within 5500 m (18,000 ft) of Earth’s surface.
99% of the mass is below 32 km (20 mi)
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6. Evolution of the Atmosphere
Primeval Phase
Earth evolved from a nebula
Gases surrounding Earth were primarily helium and hydrogen
Also hydrogen compounds, including methane and ammonia
Eventually, these escaped to space
4.4 billion years ago, enough gravity to retain an atmosphere
Outgassing – principal source of Earth’s atmosphere
Rocks outgassed as they solidified and cooled
Primarily carbon dioxide, nitrogen and water vapor
Trace amounts of methane, ammonia, sulfur dioxide, hydrogen sulfide and hydrochloric acid
Water vapor broken into hydrogen and oxygen by UV radiation
The Eagle Nebula
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Outgassing

7. Evolution of the Atmosphere
Primeval Phase
billion years ago, sun 30% fainter
CO2 combined with rainwater to form carbonic acid
Reacted with rock, locking carbon into solid, so less in atmosphere
Living organisms took CO2 out of the atmosphere via photosynthesis, locking carbon into carbohydrates
Oxygen the 2nd most abundant gas in atmosphere
Nitrogen is the 1st
Inert, out-gassing product
Nitrogen removed from atmosphere by biological and atmospheric fixation
CO2 minor component of atmosphere for the last 3.5 billion years
Fluctuations play important roles in climate change
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8. Evolution of the Atmosphere
Modern Phase
Lower atmosphere (80 km or 50 mi) circulates, maintains uniform ratios of gasses (homosphere)
Above this, gases separate based on weight
Results in stratified layers
Heterosphere
Nitrogen ~78.08%, Oxygen ~20.95% of the homosphere
Argon < 1%
CO2 < 0.04%
Oxygen
O2 in the homosphere
O in the heterosphere
150 km (95 miles) above Earth’s surface
UV radiation splits O2
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9. Evolution of the Atmosphere
Note: Water vapor varies greatly by location and so is not included.
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10. Evolution of the Atmosphere
Modern Phase
Earth’s atmosphere also has aerosols
Liquid and solid particles
Sources: wind erosion of soil, ocean spray, forest fires, volcanic eruptions, agricultural & industrial activities
Water vapor
By volume: < 4% of the lowest 1 km of the atmosphere
Necessary for clouds and precipitation
CO2 required for essential function to all life (photosynthesis)
Both CO2 and water vapor absorb and emit infrared radiation
Keeps the lower atmosphere warm
Allows for life to exist
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11. Evolution of the Atmosphere
Air pollution
Gas or aerosol that occurs at a concentration threatening the well-being of living organisms
Most are human-made, some are natural
Dust storms, volcanoes, pollen, decay of plants/animals
Primary air pollutants
Harmful immediately as emitted
Secondary air pollutants
Harmful after combination with one or more substances
Photochemical smog
Coal-fired electric power plant in Green Bay, WI.
Smog near Los Angeles, CA.
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12. Evolution of the Atmosphere
The Environmental Protection Agency (EPA)
Standards for 6 air pollutants:
carbon monoxide ■ lead ■ ozone
nitrogen oxides ■ particulates ■ sulfur dioxide
Primary air quality standards
Maximum exposure levels humans can tolerate without ill effects
Secondary air quality standards
Maximum exposure levels allowable to minimize the impact on crops, visibility, personal comfort, and climate
Compliance with standards
Attainment areas – geographic regions where standards are met or below
Non-attainment areas – geographic regions where the primary standard is not met
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13. Investigating the Atmosphere
Scientific method
Identify questions related to the problem
Propose an answer
This is an educated guess
State the educated guess in a manner that can be tested
This is the hypothesis
Predict the outcome as if the hypothesis were correct
Test the hypothesis to see if the prediction is correct
Reject or revise the hypothesis if the prediction is wrong
Scientific theory – hypothesis accepted by the scientific community
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14. Investigating the Atmosphere
Scientific models
Approximations or simulations of real system
Scientific models of the Earth-atmosphere system
Conceptual model
Statement of a fundamental law or relationship
Example: the geostrophic wind model
Graphical model
Compiles and displays data in a format that readily conveys meaning
Example: a weather map
Physical model
Miniaturized version of a system
Example: a tornado vortex chamber
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15. Investigating the Atmosphere
Purdue University's Tornado Vortex Chamber (A), which simulates tornadoes (B). This is a physical model.
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16. Investigating the Atmosphere
Scientific models of the Earth-atmosphere system
Numerical Models
Used by meteorologists
Mathematical equations represent relationships among system variables
Example: a global climate model and rising CO2
All other climate variables are held constant
CO2 is increased
Results are noted
All models have inherent errors
Missing/erroneous observational data
Accuracy of component equations may be a problem
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17. Monitoring the Atmosphere Historical Perspective
Surface Observations
Systematic observations as (in North America)
Old Swedes Fort (Wilmington, DE) had 1st systematic observations
Long-term instrument-based temperature records
1732: Philadelphia, 1738; Charleston, SC; 1753: Cambridge, MA; 1781: New Haven, CT (uninterrupted to today)
1814: Army monitored weather to understand 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 Grant established 24 stations under the U.S. Army Signal Corps
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18. Monitoring the Atmosphere
Surface Observations
1891: nation’s weather network transferred from military to civilian
New weather bureau under U.S. Department of Agriculture
1940: Transferred to Commerce Department
1965: Weather Bureau reorganized into 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.
Added Automated Surface Observing Systems (ASOS)
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19. Monitoring the Atmosphere
Automated Surface Observing System (ASOS)
Consists of electronic sensors, computers, fully automated communications ports
Feeds data to NWS Forecast Offices 24 hours a day
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20. Monitoring the Atmosphere
NWS Cooperative Observer Network
Member stations record daily precipitation, maximum and minimum temperatures
Used for hydrologic, agricultural, climatic purposes 20
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21. Monitoring the Weather Historical Perspective
Upper air observation
Kites
1749: Glasgow, Scotland, Alexander Wilson
Balloons
Manned balloon, 1804, Gay-Lussac & Biot
Air samples taken, measured temperature, humidity
Up to 7,000 m (23,000 ft)
Manned balloon, 1862, Glaisher & Coxwell
Weather measurements to 7600 m (25,000 ft)
Nearly perished from cold and oxygen deprivation
1894: carried the first thermograph aloft
: box kites with meteorographs
Up to 3000 m (10,000 ft)
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22. Monitoring the Weather Historical Perspective
Upper air observations
First radiosonde in the late 1920s.
Small instrument package equipped with a radio transmitter
Carried aloft by a helium or hydrogen filled balloon
Allowed for monitoring at higher altitudes
Transmits altitude readings of temperature, air pressure, and dewpoint
First official U.S. Weather Bureau radiosonde launched at East Boston, MA in 1937.
A radiosonde tracked from the ground to measure variations in wind direction/speed with altitude is a rawinsonde
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23. Monitoring the Atmosphere
Temperature Sensor
GPS
Pressure Sensor
Launching a radiosonde
Radiosonde
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24. Monitoring the Atmosphere
Data from radiosonde shown in a Stüve diagram
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25. Monitoring the Atmosphere
Remote Sensing
Measurement of environmental conditions by processing signals either emitted by an object or reflected back to a signal source
Radar
Satellites
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26. Temperature Profile of the Atmosphere
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27. Temperature Profile of the Atmosphere
Troposphere
Lowest layer
Weather occurs within
Temperature decreases with altitude
Exceptions: inversion, isothermal layer
Average temperature drop is 6.5 °C/1000 m (3.5 °F/1000 ft)
~6 km (3.7 mi) thick at the poles
~20 km (12 mi) thick at the equator
Tropopause
Transition zone to next layer
It is generally colder on mountain peaks than in lowlands.
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28. Temperature Profile of the Atmosphere
Stratosphere
From troposphere to ~50 km (30 mi)
In isothermal condition in lower stratosphere
Constant temperature constant
Above 20 km (12 mi), temperature increases with altitude
Stable conditions ideal for jet aircraft travel
Trap pollutants (e.g. from volcanic eruptions) in lower stratosphere
Stratopause – transition zone to next layer
Mesosphere
From stratopause up to about 80 km (50 mi)
Temperature decreases with increasing altitude
Mesosphere – transition zone to next layer
Thermosphere
Temperatures isothermal initially then rise rapidly
Sensitive to incoming solar radiation
More variable than in other regions
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29. The Ionosphere and the Aurora
Located mostly in thermosphere.
High concentration of ions and electrons
Electrically-charged, atomic-scale particles
Caused by solar energy stripping electrons from oxygen and nitrogen molecules
Leaves a positive charge
Auroras are found in ionosphere.
Caused by solar wind
Sub-atomic, super-hot, electrically charged particles
Earth’s magnetic field deflects the solar wind
Makes a teardrop-shaped cavity known as the magnetosphere
Auroras are only visible at higher latitudes
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30. The Ionosphere and the Aurora
Average variation of particle density with altitude in the ionosphere
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31. The Ionosphere and the Aurora
Magnetosphere
Caused by the deflection of the solar wind by Earth’s magnetic field
Aurora borealis
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32. The Ionosphere and the Aurora
The Northern Hemisphere auroral oval, an area of continuous auroral activity.
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