The Atmosphere

1
The Atmosphere
2
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 years

3
Basic elements of weather climate

• Air temperature
• Humidity
• Type and amount of cloudiness
• Type and amount of precipitation
• Air pressure
• The speed and direction of the wind

4
Composition of the Atmosphere

• Nitrogen 78
• Oxygen 21
• Other gases 1

5
Carbon dioxide

• Formula CO2
• Absorbs heat energy radiated by earth
• Influences heating of the atmosphere

6
Water vapor

• Formula H2O
• Varies from 0-4 composition
• Source of all clouds and precipitation
• Absorbs or release heat energy (latent heat)

7
Ozone

• 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
  (CFCs)

8
Structure of the Atmosphere

• Four layers of the atmosphere
• Troposphere
• Stratosphere
• Mesophere
• thermosphere

9
Structure of the Atmosphere (cont.)

• 50 of our atmosphere lies below an altitude of
  3.5 miles above the Earths surface

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Troposphere

• The bottom layer of the atmosphere
• Virtually all life exists in this layer
• This layer is responsible for all our weather
• Temperature of troposphere decreases with
  increasing altitude (3.5oF per 1000 ft.)
• Outer boundary is called the tropopause

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Stratosphere

• 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

12
Mesosphere

• Temperature decreases gradually with increasing
  height until one reaches the mesopause
• At that point temperature reaches around
• -90oC (-130oF)

13
Thermosphere

• Layer extends beyond the mesopause
• Temperature rise rapidly and are very high
  (gt1000oC or 1800oF)

14
Earth-Sun relationships

• Virtually all the energy that drives the earths
  weather comes from the sun
• Solar energy is not evenly distributed over the
  earths surface. Amount of energy depends on
  latitude and season
• Wind and currents are due to unequal heating of
  the earth

15
Earths motions

• Two principal motions
• 1) rotation Spinning of the earth about its
  axis
• 2) revolution movement of the earth about
  the sun.

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• At any moment, half of the earth is experiencing
  daylight, the other half darkness.
• The line separating the lighted half from the
  dark half is the circle of illumination

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Seasons

• Seasons are based on two contributing factors
• a) length of daylight
• b) angle of the sun

18

• The greater the angle of the sun, the more
  concentrated to the Earths surface.
• The suns angle is highest in summer, and lowest
  in the winter

19

• When the sun orbits the earth, the Earth tilts 23
  1/2 degrees from the perpendicular
• This is called the inclination of the axis

20

• 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

21

• During the autumnal and spring equinoxes
  (September 22 March 21), the Earth is tilted 0o
  from the sun.

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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 angles

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• 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

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• The opposite occurs during the winter solstice

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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

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Mechanisms of Heat Transfer

• Conduction
• Convection
• radiation

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Conduction

• 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

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Convection

• 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

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Radiation

• Transfer of energy through a vacuum or space
• Solar energy reaches our planet by way of
  radiation

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Forms of Radiation

• Visible
• Infrared
• Ultraviolet
• X-rays
• Microwaves
• radiowaves

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Radiation (cont.)

• All these radiations constitutes a collection of
  radiations called an electromagnetic spectrum
• Each of these radiations have a characteristic
  wavelength
• Wavelength Distance from one crest to the next

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Visible radiation

• Radiation which can be seen by our eyes.
• Visible radiation can be broken down into its
  seven colors (what are the colors?)

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Infrared radiation

• Radiation is longer in wavelength than visible
  light
• Lies above the red region of the visible spectrum
• Responsible for heat radiation

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Ultraviolet radiation

• Shorter wavelength than visible radiation
• Lies below the violet region of the visible
  spectrum
• Primary source of radiation from the sun.
  Responsible for sunburn

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Basic Laws of Radiation

• All objects give off radiation, regardless of
  temperature
• Hotter objects give off more radiation than
  colder objects
• The hotter the radiating body, the shorter the
  wavelength of maximum energy
• Objects that are good absorbers are also good
  emitters as well

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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

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Solar radiation and our Earth

• About 50 of the solar energy reaching the
  atmosphere is absorbed by the Earths surface
• About 30 is reflected back into space by the
  atmosphere, clouds, and other reflective surfaces
• About 20 is absorbed by clouds and the
  atmospheres gases

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Reflection

• 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

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Absorption

• Gases are selective absorbers
• Nitrogen is a poor absorber of solar radiation
• Oxygen removes most of the shorter wavelength
  ultraviolet radiation and ozone absorbs most of
  the ultraviolet rays from the stratosphere

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Albedo

• The fraction of radiation that is reflected by
  the earths surface
• Albedo of the Earth, as a whole is 30
• Albedo varies on Earth from place to place and
  from time to time

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Factors affecting albedo

• Amount of cloud cover
• Suns angle
• Presence of particulate matter
• Nature of the Earths surface

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Scattering

• 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

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The greenhouse effect

• This is the increase in the temperature of a
  planets atmosphere caused when
  infrared-absorbing gases are introduced into the
  atmosphere

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• 50 of the solar energy that strikes the Earths
  surface is absorbed
• Most of this radiation is radiated skyward
• The radiation that the Earth gives off has longer
  wavelengths than solar radiation

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Greenhouse gases

• Carbon dioxide
• Water vapor

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Principles behind the greenhouse effect

• Short wavelength radiation from the sun passes
  through the atmosphere and is absorbed by the
  Earths 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

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• Without the greenhouse effect, life on our planet
  will not exist

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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
  combined
• The concentration of water vapor increases with
  altitude

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Carbon dioxide

• Carbon dioxide, like water, contributes to the
  greenhouse effect
• Carbon dioxide is an important heat absorber
• A change in the atmospheres carbon dioxide
  content can influence air temperature

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Global warming

• Earths industrialization is fueled by the
  burning of fossil fuels.
• Sources of fossil fuels coal, natural gas,
  petroleum.

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Contributors of carbon dioxide release

• Burning of fossil fuels
• The clearing of forests (deforestation)

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• Out of all the carbon dioxide available, 45-50
  remains in the atmosphere

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The atmospheres 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

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Possible consequences

• Probable rise in sea levels
• Potential weather changes
• Stronger tropical storms
• Increases in the frequency of heat waves and
  droughts

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Temperature controls

• A factor that causes temperature to vary from
  place to place and from time to time

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Air temperature data

• Types of air temperature data compiled by
  meteorologists
• a) daily mean temperature
• b) daily range of temperature
• c) monthly mean temperature
• d) annual mean temperature
• e) annual temperature range

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Daily mean temperature

• This is determined by adding the maximum and
  minimum temperatures and then dividing by two

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Daily temperature range

• This is computed by finding the difference
  between the maximum and minimum temperatures for
  a given day

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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

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Annual mean temperature

• This is the average of the 12 monthly means

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Annual temperature range

• This is computed by finding the difference
  between the highest and lowest monthly means

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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