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The Atmosphere


									The Atmosphere
        Weather vs. climate
 Weather: The state of the atmosphere at
  a given time (hour to hour or day to day)
 Climate: A description of aggregate
  weather conditions, based on observations
  that take place in a region over a period of
    Basic elements of weather &
 Air temperature
 Humidity
 Type and amount of cloudiness
 Type and amount of precipitation
 Air pressure
 The speed and direction of the wind
Composition of the Atmosphere
 Nitrogen: 78%
 Oxygen: 21%
 Other gases 1%
           Carbon dioxide
 Formula: CO2
 Absorbs heat energy radiated by earth
 Influences heating of the atmosphere
             Water vapor
 Formula: H2O
 Varies from 0-4% composition
 Source of all clouds and precipitation
 Absorbs or release heat energy (latent
 Formula: O3
 Allotrope of oxygen
 Highly toxic
 Ozone is concentrated in the stratosphere
 Ozone absorbs harmful ultraviolet
  radiation from the sun
 Ozone is being slowly depleted from the
  atmosphere due to use of
  chlorofluorocarbons (CFC’s)
  Structure of the Atmosphere
Four layers of the atmosphere
1) Troposphere
2) Stratosphere
3) Mesophere
4) thermosphere
     Structure of the Atmosphere
   50% of our atmosphere lies below an
    altitude of 3.5 miles above the Earth’s
 The bottom layer of the atmosphere
 Virtually all life exists in this layer
 This layer is responsible for all our
 Temperature of troposphere decreases
  with increasing altitude (3.5oF per 1000 ft.)
 Outer boundary is called the tropopause
 This layer lies beyond the tropopause
 Temperature remains constant to height of
  13 miles, then the temperature will
  gradually increase
 Ozone is concentrated in this layer
 Outer layer is called the stratopause
 Temperature decreases gradually with
  increasing height until one reaches the
 At that point temperature reaches around
  -90oC (-130oF)
 Layer extends beyond the mesopause
 Temperature rise rapidly and are very high
  (>1000oC or 1800oF)
      Earth-Sun relationships
 Virtually all the energy that drives the
  earth’s weather comes from the sun
 Solar energy is not evenly distributed over
  the earth’s surface. Amount of energy
  depends on latitude and season
 Wind and currents are due to unequal
  heating of the earth
              Earth’s motions
   Two principal motions:
    1) rotation: Spinning of the earth about its
    2) revolution: movement of the earth
    about the sun.
 At any moment, half of the earth is
  experiencing daylight, the other half
 The line separating the lighted half from
  the dark half is the circle of illumination
   Seasons are based on two contributing
    a) length of daylight
    b) angle of the sun
 The greater the angle of the sun, the more
  concentrated to the Earth’s surface.
 The sun’s angle is highest in summer, and
  lowest in the winter
 When the sun orbits the earth, the Earth
  tilts 23 1/2 degrees from the
 This is called the inclination of the axis
 During the summer solstice (June 21), the
  Northern Hemisphere is leaning 23 ½
  degrees towards the sun
 During the winter solstice (December 21),
  the Northern Hemisphere is leaning 23 ½
  degrees away from the sun
   During the autumnal and spring equinoxes
    (September 22 & March 21), the Earth is
    tilted 0o from the sun.
    Facts about the summer solstice
 Occurs June 21 or 22
 Vertical rays of the sun are striking the
  Tropic of Cancer (23 ½ north latitude)
 Northern Hemisphere are experiencing the
  greatest length of daylight
 Locations north of the Tropic of Cancer
  are experiencing the highest noon Sun
   The farther you are north of the equator,
    the longer the period of daylight, until the
    Arctic Circle is reached, where the daylight
    lasts for 24 hours
   The opposite occurs during the winter
        Heat & Heat transfer
 Heat: Form of energy that moves from a
  warmer body to a cooler body
 If two objects of unequal temperature are
  in contact with each other, heat will travel
  from the warmer body to the cooler body.
 The temperature of the warmer will
  decrease, temperature of the cooler body
  will increase
     Mechanisms of Heat Transfer
1)   Conduction
2)   Convection
3)   radiation

 Transfer of heat through matter by
  molecular activity
 Transfer occurs by collisions from one
  molecule to another
 Conduction of heat varies from one
  material to another
 Metals are the best heat conductors
 Transfer of heat by mass movement or
  circulation within a substance
 Convection primarily takes place in fluids
 This is the type of heat transfer that
  primarily occurs in the atmosphere
 Transfer of energy through a vacuum or
 Solar energy reaches our planet by way of
          Forms of Radiation
1)   Visible
2)   Infrared
3)   Ultraviolet
4)   X-rays
5)   Microwaves
6)   radiowaves
           Radiation (cont.)
 All these radiations constitutes a collection
  of radiations called an electromagnetic
 Each of these radiations have a
  characteristic wavelength
 Wavelength: Distance from one crest to
  the next
           Visible radiation
 Radiation which can be seen by our eyes.
 Visible radiation can be broken down into
  its seven colors (what are the colors?)
          Infrared radiation
 Radiation is longer in wavelength than
  visible light
 Lies above the red region of the visible
 Responsible for heat radiation
         Ultraviolet radiation
 Shorter wavelength than visible radiation
 Lies below the violet region of the visible
 Primary source of radiation from the sun.
  Responsible for sunburn
       Basic Laws of Radiation
1)   All objects give off radiation, regardless
     of temperature
2)   Hotter objects give off more radiation
     than colder objects
3)   The hotter the radiating body, the shorter
     the wavelength of maximum energy
4)   Objects that are good absorbers are also
     good emitters as well
Fate of incoming solar radiation
When radiation strikes an object, three
 possible outcomes can occur:
1) Radiation can be absorbed by the object
2) Radiation can be transmitted (go
 through) the object
3) Radiation can be reflected (bounced off)
 an object
    Solar radiation and our Earth
 About 50% of the solar energy reaching
  the atmosphere is absorbed by the Earth’s
 About 30% is reflected back into space by
  the atmosphere, clouds, and other
  reflective surfaces
 About 20% is absorbed by clouds and the
  atmosphere’s gases
 About 30% of the solar energy reaching
  the outer atmosphere is reflected back to
  the space
 This fraction of total radiation that is
  reflected is called albedo
 Gases are selective absorbers
 Nitrogen is a poor absorber of solar
 Oxygen removes most of the shorter
  wavelength ultraviolet radiation and ozone
  absorbs most of the ultraviolet rays from
  the stratosphere
 The fraction of radiation that is reflected by
  the earth’s surface
 Albedo of the Earth, as a whole is 30%
 Albedo varies on Earth from place to place
  and from time to time
     Factors affecting albedo
 Amount of cloud cover
 Sun’s angle
 Presence of particulate matter
 Nature of the Earth’s surface
 Occurs when a beam of light produces a
  larger number of weaker rays
 The weaker rays travel in all directions
 Scattering of light accounts for the
  blueness of our sky
         The greenhouse effect
   This is the increase in the temperature of a
    planet’s atmosphere caused when
    infrared-absorbing gases are introduced
    into the atmosphere
 50% of the solar energy that strikes the
  Earth’s surface is absorbed
 Most of this radiation is radiated skyward
 The radiation that the Earth gives off has
  longer wavelengths than solar radiation
        Greenhouse gases
 Carbon dioxide
 Water vapor
    Principles behind the greenhouse
 Short wavelength radiation from the sun
  passes through the atmosphere and is
  absorbed by the Earth’s surface
 Energy is emitted from the surface as
  long-wavelength radiation
 Much of this radiation is absorbed by
  certain gases in the atmosphere
 Radiation absorbed by the atmosphere is
  reradiated skyward
   Without the greenhouse effect, life on our
    planet will not exist
              Water vapor
 Water vapor is an excellent absorber of
  long-wavelength (infrared) radiation
 Water vapor absorbs five times as much
  terrestrial radiation than all other gases
 The concentration of water vapor
  increases with altitude
            Carbon dioxide
 Carbon dioxide, like water, contributes to
  the greenhouse effect
 Carbon dioxide is an important heat
 A change in the atmosphere’s carbon
  dioxide content can influence air
            Global warming
 Earth’s industrialization is fueled by the
  burning of fossil fuels.
 Sources of fossil fuels: coal, natural gas,
    Contributors of carbon dioxide
 Burning of fossil fuels
 The clearing of forests (deforestation)
   Out of all the carbon dioxide available, 45-
    50% remains in the atmosphere
    The atmosphere’s response
 The global average temperature increased
  by about 1oF since the mid 1970s and total
  warming in the past century has increased
  by 1.4oF
 The 1990s was the warmest decade, in
  recent memory
     Possible consequences
 Probable rise in sea levels
 Potential weather changes
 Stronger tropical storms
 Increases in the frequency of heat waves
  and droughts
         Temperature controls
   A factor that causes temperature to vary
    from place to place and from time to time
          Air temperature data
   Types of air temperature data compiled by
    a) daily mean temperature
    b) daily range of temperature
    c) monthly mean temperature
    d) annual mean temperature
    e) annual temperature range
       Daily mean temperature
   This is determined by adding the
    maximum and minimum temperatures
    and then dividing by two
       Daily temperature range
   This is computed by finding the difference
    between the maximum and minimum
    temperatures for a given day
     Monthly mean temperature
   This is calculated by adding the daily
    temperature means for each day of the
    month and dividing by the number of days
    in the month
      Annual mean temperature
   This is the average of the 12 monthly
      Annual temperature range
   This is computed by finding the difference
    between the highest and lowest monthly
    Air temperature data (cont.)
 Isotherms are commonly used to examine
  the distribution of air temperatures over
  large areas
 Isotherm: A line that connects points on a
  map that have the same temperature

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