Ch 22-Atmosphere

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Ch 22-Atmosphere

• Objectives
• Composition of Earths 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

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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 elementsnitrogen, oxygen, argon
• Most abundant compounds in airCO2and 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

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Atmospheric Pressure

• Atmospheric pressurethe 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 atm760 mm of
  mercury1000 millibars
• Barometer-instrument used to measure atmospheric
  pressure
• Mercurial and aneroid barometers

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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

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• 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

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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?

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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

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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 Earths axis, water vapor and
  CO2, wind patterns

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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

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Atmospheric Circulation

• Coriolis Effect-curving of the path of a moving
  object from an otherwise straight path due to
  Earths rotation
• Deflects moving objects along a path that depends
  on speed, latitude, and direction of the object
• http//glencoe.com/sec/science/earthscience/2007/c
  oncept_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

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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

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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

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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

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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

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Measuring Humidity

• Thin polymer film
• Psychrometers
• Dew cell
• Hair hygrometer
• Radiosonde
• Why measure humidity?

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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 Earths 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

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• 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

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Types of Clouds

• Classified by shape and altitude
• Stratus-flat, uniform base, low altitudes
• Base is low, close to Earths 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

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• Altocumulus-4000 m

• Cumulonimbus-2000 to 6000 m

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• Cirrus-8000 m

• Nimbostratus-1000 m

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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?

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Precipitation

• Define precipitation
• Any form of water that falls to Earths 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

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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

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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