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Ch 22-Atmosphere Objectives Composition of Earth’s atmosphere

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1 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

2 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

3 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

4 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

5 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

6 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?

7 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


9 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

10 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

11 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 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 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

12 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

13 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

14 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

15 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

16 Measuring Humidity Thin polymer film Psychrometers Dew cell
Hair hygrometer Radiosonde Why measure humidity?

17 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

18 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

19 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

20 Altocumulus-4000 m Cumulonimbus-2000 to 6000 m

21 Cirrus-8000 m Nimbostratus-1000 m

22 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?

23 Precipitation Define precipitation Rain, snow, sleet, hail
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

24 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

25 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

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