1. AP Environmental Science
Mr. Grant
Lesson 45
The Atmosphere

2. 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.

3. 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.

4. 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.

5. 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)

6. The atmosphere’s composition

7. 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

8. 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)

9. The atmosphere’s four layers
Atmospheric layers have different
Temperatures
Densities
Composition

10. 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

11. 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.

12. 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

13. 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

14. 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
Replacing rising warm air
Convection influences weather and climate

15. 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”

16. 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
Cold front = where colder, drier air displaces warmer, moister air
Warm fronts produce light rain
Cold fronts produce thunderstorms

17. 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

18. 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

19. 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

20. 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

21. Climate patterns and moisture distribution

22. 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

23. 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)

24. 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

25. Rachel Pike: The science behind a climate headline (4:14)
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)