Ch 22-Atmosphere• Objectives

– Composition of Earth’s atmosphere– Layers of atmosphere– Effects of air pollution– How radiant energy reaches Earth– How visible light and infrared energy warm Earth– Summarize the processes of radiation, conduction, and convection– Explain the Coriolis effect– Global patterns of air circulation, and name global wind belts– Identify factors that form local win patterns– Explain how heat energy affects the changing phases of water– Explain what absolute and relative humidity are, describe how they are

measured– Describe what happens when the temp of air decreases to the dew pt or

below the dew pt– Describe the conditions that are necessary for clouds to form– Explain the processes of cooling that can lead to formation of clouds– Identify the types of clouds– Describe ways in which fog can form– Processes that cause precipitation– Explain how rain can be produced artificially

Characteristics of Atmosphere• Define atmosphere

– Mixture of gases that surrounds a planet • Air-the atmosphere that is made up of a mixture of chemical

elements and compounds. What is the function of air?• Composition of Atmosphere

– Most abundant elements=nitrogen, oxygen, argon– Most abundant compounds in air=CO₂and H₂O– Dust and pollen

• Water vapor-enters air as invisible gas• Ozone in the Atmosphere

– Ozone-gas molecule that is made up of 3 oxygen atoms– Why is ozone layer important?– Chlorofluorocarbons-used in fridges and air conditioners-break

down ozone and cause layer to weaken

Atmospheric Pressure

• Atmospheric pressure=the force per unit area exerted on a surface by weight of atmosphere– Pressure is exerted equally in all directions– Atmospheric pressure decreases as altitude increases– Pressure changes as a result of differences in temp and in

amount of water vapor. Why?

• Measuring Atmospheric Pressure– 3 units used for atmospheric pressure-atmospheres (atm),

millimeters or inches of mercury, and millibars– Standard atmospheric pressure- 1 atm=760 mm of

mercury=1000 millibars– Barometer-instrument used to measure atmospheric pressure

• Mercurial and aneroid barometers

Layers of Atmosphere

• What are the layers?– Troposphere, Stratosphere, Mesosphere, Thermosphere

• Characteristics of Troposphere– Closest to Earth– Nearly all the weather– Temp decreases w/ altitude – Average altitude of 12 km-varies w/ latitude and season

• Characteristics of Stratosphere– Lies between Troposphere and Mesosphere– Ozone layer– Temp increases w/ altitude – Layer heated by absorption of solar radiation by ozone– Extends to about 50 km in altitude

• Characteristics of Mesosphere– Lies bet Stratosphere and Thermosphere– Extends to about 80 km in altitude– Temp decreases as altitude increases– Avg temp of -90 deg C-coldest temp in

atmosphere

• Characteristics of Thermosphere– Temp increases as altitude increases-Nitrogen

and oxygen atoms absorb solar radiation– Extends from 80 to 400 km– Ionosphere and exosphere– Uppermost layer of atmosphere

• Concepts in Motion

Air Pollution

• What is the main source of pollution?– Burning of fossil fuels, coal and petroleum– Release sulfur dioxide gas, hydrocarbons,

nitrogen oxides, carbon monoxides, lead

• Smog-combination of smoke and fog

• Air cannot circulate up and away from area

• How can air pollution be controlled?

Solar Energy and Radiation• Radiation-all forms of energy that travel through space as

waves– Visible light, ultraviolet light, x rays, radio waves– Very high speed

• Electromagnetic waves-waves that make up all forms of radiation– Almost all forms of energy that reaches Earth

• Electromagnetic spectrum-all of the frequencies or wavelengths of electromagnetic radiation

• Upper atmosphere-ultraviolet rays, x rays, gamma rays absorbed here

• Lower atmosphere-visible and infrared waves absorbed here• Scattering and reflection

– Albedo-is the fraction of solar radiation that is reflected off the surface of an object

Absorption and Infrared Energy

• Radiation absorbed by rocks, soil, water• Infrared rays and visible light heat surface

materials• What is the greenhouse effect?

– Warming of the surface and lower atmosphere of Earth that occurs when CO₂, water vapor, and other gases in the air absorb and reradiate infrared radiation

• What affects temperature of the atmosphere?– Latitude, tilt of Earth’s axis, water vapor and CO₂,

wind patterns

Conduction and Convection

• Conduction-transfer of energy as heat moves through a material– Solid substances– Heats only lowest few cm of atmosphere

• Convection-movement of matter due to differences in density that are caused by temperature variations– Lower atmosphere heating occurs when gases

or liquids are heated unevenly

• Concepts in Motion

Atmospheric Circulation• Coriolis Effect-curving of the path of a moving object from an

otherwise straight path due to Earth’s rotation– Deflects moving objects along a path that depends on speed,

latitude, and direction of the object– http://glencoe.com/sec/science/earthscience/2007/concept_motion/

NGS/Visualizing_the_Coriolis_Effect_12.swf• Global winds

– Trade winds-flow toward the equator between 30 and 0 deg. NE and SE trade winds

– Westerlies-prevailing winds that blow throughout the contiguous United States

– Polar Easterlies-about 60 deg latitude, zone of low pressure. Winds blow from east to west bet 60-90 deg

– Doldrums and Horse latitudes- where trade wind systems meet at equator, air movement is upward, surface winds are weak

– Jet streams-narrow band of strong winds that blow in the upper troposphere

Local Winds

• Local conditions and local temps cause local winds

• Breezes-gentle winds that extend over distances of less than 100 km

• Land breeze-blows cool air from land to water• Sea breeze-cool wind moving from water to

land. Forms in afternoon• Mt breeze-at nighttime, cool air descends

from mt peaks• Valley breeze-forms when warm air from

valleys moves upslope, during daylight hrs

Atmospheric Moisture

• What are the phases of water?• How does water change?

– Heat energy is absorbed or released

• Latent heat-heat energy that is absorbed or released by a substance during a phase change

• Condensation-water vapor changes back into a liquid, energy is released to surrounding air, molecules move closer together

• Evaporation-water molecules move so rapidly that they collide and escape from liquid, form invisible water vapor– Where does evaporation occur at most?

• Sublimation-solid changes directly into a gas

Humidity

• Water vapor in atmosphere• What controls humidity?

– Condensation and evaporation

• Dew pt-the temp at which rate of condensation equals rate of evaporation

• Absolute humidity-mass of water vapor contained in a given volume of air

• Relative humidity-ratio of the actual water vapor content of the air to the amount of water vapor needed to reach saturation

Dew Point

• Air is warmer than objects near the ground, air may cool to its dew point by conduction when air is in contact w/ cold surface

• Cool, clear nights, little wind

• Dew pt falls below freezing temp of water= water vapor changes directly into solid ice crystals or frost

Measuring Humidity

• Thin polymer film

• Psychrometers

• Dew cell

• Hair hygrometer

• Radiosonde

• Why measure humidity?

Clouds and Fog

• Clouds-collections of small water droplets or ice crystals that fall slowly through the air

• Form when condensation or crystallization occurs more rapidly than evaporation or sublimation does

• Fog-a cloud that forms near or on Earth’s surface• Cloud Formation

– Solid surface for condensation to take place– Condensation nuclei-solid particle in the atmosphere that

provides surface on which water vapor condenses– Rate of evaporation in equilibrium w/ rate of condensation, air

becomes saturated w/ water vapor– Temp drops, condensation occurs more rapidly than evaporation

does

• Adiabatic Cooling-temp of an air mass decreases as the air mass rises and expands– Air cools to temp below dew pt, net condensation causes clouds to

form– Condensation level-base of clouds

• Mixing-body of moist air mixes w/ another body of moist air that has different temp– Combination of air causes temp to change

• Lifting-air is forced upward when moving mass of air meets sloping terrain, mt range, rising air expands and cools, clouds form

• Advective cooling-temp of air mass decreases as air mass moves over a cold surface– Cold ocean or land surface– Cold surface absorbs heat from air and cools it, air cools to below

dew pt, clouds form

Types of Clouds• Classified by shape and altitude• Stratus-flat, uniform base, low altitudes

– Base is low, close to Earth’s surface– Cover large area, block out sun– Little precipitation– Nimbostratus and altostratus

• Cumulus-low altitude, billowy, top that resembles cotton balls and dark bottom– Look fluffy– Warm, moist air rises and cools, cooling air reaches dew pt, clouds form

• Cumulonimbus-high dark storm clouds– Thunderheads– Altocumulus and stratocumulus

• Cirrus-feathery clouds composed of ice crystals w/ highest altitude– Altitudes of 6000 m– Cirrocumulus and cirrostratus

Altocumulus-4000 m Cumulonimbus-2000 to 6000 m

Cirrus-8000 m Nimbostratus-1000 m

Fog

• What causes fog?– Condensation of water vapor in air

• Forms from nightly cooling of Earth, air comes in contact w/ chilled ground to below dew pt, water vapor in air condenses into droplets

• Thickest in valleys and low places. Why?

• Also thick around cities. Why?

Precipitation

• Define precipitation– Any form of water that falls to Earth’s surface from the

clouds

• Rain, snow, sleet, hail• Causes of precipitation

– Coalescence-formation of large droplet by combination of smaller droplets

– Supercooling-condition in which substance is cooled below its freezing pt, condensation pt, or sublimation pt w/out going through a change of state

Measuring Precipitation

• Doppler Radar-can measure intensity of precipitation– Used by meteorologists for communicating

weather – Bounces radio waves off rain or snow– Determine the location, direction of

movement, intensity of precipitation

Weather Modifications

• Cloud seeding-introducing freezing nuclei or condensation nuclei into a cloud to cause rain to fall

• Uses silver iodide as freezing nuclei

• Use powdered dry ice, dropped from aircraft to cool cloud droplets, cause ice crystals to form