The Atmosphere

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 • The spatial relationship between the Earth and sun determines how much solar energy strikes the Earth • Microclimate = a localized pattern of weather conditions • Energy from the sun: • Heats and moves air • Creates seasons • Influences weather and climate • Solar radiation is highest near the equator

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. 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 Air masses produce weather 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. 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. Rachel Pike: The science behind a climate headline (4:14) 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.