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AP Environmental
Science
Mr. Grant
Lesson 45
The Atmosphere
© 2011 Pearson Education, Inc.
Objectives:
• Define the terms weather and climate.
• Describe the composition, structure, and function of
Earth’s atmosphere.
• Relate weather and climate to atmospheric conditions.
• TED - In 4 minutes, atmospheric chemist Rachel Pike
provides a glimpse of the massive scientific effort behind
the bold headlines on climate change, with her team -one of thousands who contributed -- taking a risky flight
over the rainforest in pursuit of data on a key molecule.
© 2011 Pearson Education, Inc.
Define the terms weather and climate.
Weather: The local physical properties of the
troposphere, such as temperature, pressure, humidity,
cloudiness, and wind over relatively short time periods.
Climate: The pattern of atmospheric conditions found
across large geographic regions over long periods of
time.
© 2011 Pearson Education, Inc.
Describe the composition, structure, and
function of Earth’s atmosphere.
• The atmosphere consists of 78% nitrogen gas, 21%
oxygen gas, and a variety of other gases in minute
concentrations.
• The atmosphere includes four principal layers: the
troposphere, stratosphere, mesosphere, and
thermosphere. Temperature and other characteristics
vary across these layers. Ozone is concentrated in the
stratosphere.
© 2011 Pearson Education, Inc.
The atmosphere
• Atmosphere = the thin layer of gases around Earth
- Provides oxygen
- Absorbs radiation and moderates climate
- Transports and recycles water and nutrients
- 78% N2, 21% O2
• Minute concentrations of permanent (remain at stable
concentrations) gases
- Variable gases = varying concentrations across time
and place
• Human activity is changing the amount of some gases
- CO2, methane (CH4), ozone (O3)
© 2011 Pearson Education, Inc.
The atmosphere’s composition
© 2011 Pearson Education, Inc.
The first two layers of the atmosphere
• Troposphere = bottommost layer (11 km [7 miles])
- Air for breathing, weather
- The air gets colder with altitude
- Tropopause = limits mixing between troposphere
and the layer above it
• Stratosphere = 11–50 km (7–31 mi) above sea level
- Drier and less dense, with little vertical mixing
- Becomes warmer with altitude
- Contains UV radiation-blocking ozone, 17–30 km
(10–19 mi) above sea level
© 2011 Pearson Education, Inc.
The two highest levels of the atmosphere
• Mesosphere = 50–80 km (31–56 mi) above sea level
- Extremely low air pressure
- Temperatures decrease with altitude
• Thermosphere = atmosphere’s top layer
- Extends upward to 500 m (300 mi)
© 2011 Pearson Education, Inc.
The atmosphere’s four layers
• Atmospheric layers
have different
- Temperatures
- Densities
- Composition
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Atmospheric properties
• Atmospheric pressure =
the force per unit area
produced by a column of air
• Relative humidity = the
ratio of water vapor air
contains to the amount it
could contain at a given
temperature
- High humidity makes it
feel hotter than it really is
• Temperature = varies with
location and time
Atmospheric pressure
decreases with altitude
© 2011 Pearson Education, Inc.
Relate weather and climate to atmospheric
conditions.
• The sun’s energy heats the atmosphere, drives air
circulation, and helps determine weather, climate, and
the seasons.
• Weather is a short-term phenomenon, whereas climate
is a long-term phenomenon. Fronts, pressure systems,
and the interactions among air masses influence
weather.
• Global convective cells called Hadley, Ferrel, and polar
cells create latitudinal climate zones.
• Hurricanes and tornadoes are types of cyclonic storms
that can threaten life and property.
© 2011 Pearson Education, Inc.
Solar energy heats the atmosphere
• Energy from the sun:
- Heats and moves air
- Creates seasons
- Influences weather
and climate
• Solar radiation is highest
near the equator
• The spatial relationship between the Earth and sun
determines how much solar energy strikes the Earth
• Microclimate = a localized pattern of weather conditions
© 2011 Pearson Education, Inc.
Solar energy creates seasons
• Because the Earth is tilted, each hemisphere tilts
toward the sun for half the year
- Results in a change of seasons
Equatorial regions are
unaffected by this tilt, so
days average 12 hours
throughout the year
© 2011 Pearson Education, Inc.
Solar energy causes air to circulate
• Air near Earth’s surface is
warm and moist
• Convective circulation =
less dense, warmer air rises
- Creating vertical currents
- Rising air expands and
cools
- Cool air descends and
becomes denser
Convection influences
weather and climate
- Replacing rising warm
air
© 2011 Pearson Education, Inc.
The atmosphere drives weather and climate
• Weather and climate involve the physical properties of
the troposphere
- Temperature, pressure, humidity, cloudiness, wind
• Weather = specifies atmospheric conditions over short
time periods and within small geographic areas
• Climate = patterns of atmospheric conditions across
large geographic regions over long periods of time
• Mark Twain said, “Climate is what we expect; weather
is what we get”
© 2011 Pearson Education, Inc.
Air masses produce weather
• Front = the boundary between
air masses that differ in
temperature, moisture, and
density
• Warm front = boundary
where warm, moist air
replaces colder, drier air
Warm fronts produce
light rain
• Cold front = where colder,
drier air displaces warmer,
moister air
Cold fronts produce
thunderstorms
© 2011 Pearson Education, Inc.
Air masses have different pressures
• High-pressure system = air that descends because it is
cool
- It spreads outward as it nears the ground
- Brings fair weather
• Low-pressure system = warm air rises and draws air
inward toward the center of low pressure
- Rising air expands and cools
- It brings clouds and precipitation
© 2011 Pearson Education, Inc.
Thermal (temperature) inversion
• Air temperature decreases as altitude increases
- Warm air rises, causing vertical mixing
• Thermal inversion = a layer of
cool air occurs beneath warm
air
• Inversion layer = the band of
air where temperature rises with
altitude
- Denser, cooler air at the
bottom of the layer resists
mixing
• Inversions trap pollutants in
cities surrounded by mountains
© 2011 Pearson Education, Inc.
Circulation systems produce climate patterns
• Convective currents contribute to climatic patterns
• Hadley cells = convective cells near the equator
- Surface air warms, rises, and expands
- Causing heavy rainfall near the equator
- Giving rise to tropical rainforests
• Currents heading north and south are dry
- Giving rise to deserts at 30 degrees
• Ferrel cells and polar cells = lift air and create
precipitation at 60 degrees latitude north and south
- Conditions at the poles are dry
© 2011 Pearson Education, Inc.
Global wind patterns
• Atmospheric cells interact with Earth’s rotation to
produce global wind patterns
- As Earth rotates, equatorial regions spin faster
• Coriolis effect = the apparent north-south deflection of
air currents of the convective cells
- Results in curving global wind patterns called the
doldrums, trade winds, and westerlies
© 2011 Pearson Education, Inc.
Climate patterns and moisture distribution
© 2011 Pearson Education, Inc.
Global wind patterns
• Doldrums = a region near the equator with few winds
• Trade winds = between the equator and 30 degrees
- Blow from east to west
- Weaken periodically, leading to El Niño conditions
• Westerlies = from 30 to 60 degrees latitude
- Blow from west to east
• People used these winds to sail across the ocean
• Wind and convective circulation in ocean water maintain
ocean currents
- And can create violent storms
© 2011 Pearson Education, Inc.
Storms pose hazards
• Atmospheric conditions can produce dangerous storms
• Hurricanes = form when winds rush into areas of low
pressure
- Warm, moist air over the topical oceans rises
• Typhoons (cyclones) = winds turn counterclockwise in
the Northern Hemisphere
- Drawing up huge amounts of water vapor
- Which falls as heavy rains
• Tornadoes = form when warm air meets cold air
- Quickly rising warm air forms a powerful convective
current (spinning funnel)
© 2011 Pearson Education, Inc.
Hurricanes and tornadoes
• Understanding how the atmosphere works helps us to:
- Predict violent storms and protect people
- Comprehend how pollution affects climate,
ecosystems, and human health
© 2011 Pearson Education, Inc.
TED Video
Rachel Pike studies climate change at
the molecular level -- tracking how
emissions from biofuel crops react with
the air to shape weather trends
globally.
In 4 minutes, atmospheric chemist Rachel Pike provides a glimpse of the
massive scientific effort behind the bold headlines on climate change,
with her team -- one of thousands who contributed -- taking a risky flight
over the rainforest in pursuit of data on a key molecule.
Rachel Pike: The science behind a climate headline (4:14)
© 2011 Pearson Education, Inc.