AP Environmental Science Mr. Grant Lesson 45 The Atmosphere

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.

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.

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.

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)

The atmosphere’s composition

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

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)

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

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

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.

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

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

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

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”

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

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

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

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

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

Climate patterns and moisture distribution

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

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)

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

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)