AMS Weather Studies
Introduction to Atmospheric Science, 5th Edition
Chapter 2
Atmosphere: Origin,
Composition, & Structure
© AMS
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
2
© AMS
Atmosphere viewed from space
3
© AMS
Case-in-Point
African Origins of WindBorne 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.
4
© AMS
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)
5
© AMS
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
The Eagle Nebula
 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
6
UV radiation
Outgassing
© AMS
Evolution of the Atmosphere
 Primeval Phase
 4.5-2.5 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 7in climate change
© AMS
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
8
 UV radiation splits O2
© AMS
Evolution of the Atmosphere
Note: Water vapor
varies greatly by
location and so is
not included.
9
© AMS
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
10
 Allows for life to exist
© AMS
Evolution of the Atmosphere
 Air pollution
 Gas or aerosol that occurs at a
concentration threatening the well-being
of living organisms
Coal-fired electric power plant
 Most are human-made, some are natural
in Green Bay, WI.
 Dust storms, volcanoes, pollen, decay of
plants/animals
 Primary air pollutants
Smog near Los Angeles, CA.
 Harmful immediately as emitted
 Secondary air pollutants
 Harmful after combination with one or more
substances
 Photochemical smog
11
© AMS
Evolution of the Atmosphere
 The Environmental Protection Agency (EPA)
 Standards for 6 air pollutants:
 carbon monoxide
 nitrogen oxides
lead
■ particulates
■
ozone
■ 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
12
© AMS
not met
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
13
© AMS
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
14
© AMS
Investigating the Atmosphere
Purdue University's Tornado Vortex Chamber (A), which simulates tornadoes (B).
15
© AMS
This is a physical model.
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
16
© AMS
Monitoring the Atmosphere
Historical Perspective
 Surface Observations
 Systematic observations as 1644-45 (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
17
© AMS
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)
18
© AMS
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
19
© AMS
Monitoring the Atmosphere
 NWS Cooperative Observer Network
 Member stations record daily
precipitation, maximum and minimum
temperatures
 Used for hydrologic, agricultural, climatic
purposes
20
© AMS
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
 Kites
 1894: carried the first thermograph aloft
 1907-1933: box kites with meteorographs
 Up to 3000 m (10,000 ft)
21
© AMS
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
22
© AMS
Monitoring the Atmosphere
Temperature
Sensor
GPS
Pressure
Sensor
Radiosonde
Launching a radiosonde
23
© AMS
Monitoring the Atmosphere
Data from radiosonde
shown in a Stüve diagram
24
© AMS
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
25
© AMS
Temperature Profile of the Atmosphere
26
© AMS
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)
It is generally colder
on mountain peaks
than in lowlands.
 ~6 km (3.7 mi) thick at the poles
 ~20 km (12 mi) thick at the equator
 Tropopause
 Transition zone to next layer
27
© AMS
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 28
 More variable than in other regions
© AMS
The Ionosphere and the Aurora
 Ionosphere
 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
29
© AMS
The Ionosphere and the Aurora
Average variation of particle density with altitude in the ionosphere
30
© AMS
The Ionosphere and the Aurora
 Magnetosphere
 Caused by the deflection of the solar wind by Earth’s magnetic field
Aurora borealis
31
© AMS
The Ionosphere and the Aurora
The Northern
Hemisphere
auroral oval, an
area of continuous
auroral activity.
32
© AMS