The vertical structure of the atmosphere

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Chapter 1

• The vertical structure of the atmosphere

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Pressure and density

• Density is a measure of the amount of mass per
  unit volume
• Density mass/volume
• Gravity acts to keep the bulk of the atmospheres
  mass near the earths surface, so air is most
  dense near the surface and decreases with height
• As a general rule, no matter where you are in the
  atmosphere if you ascend 5.6 km you will have
  reduced the atmospheric mass above you by half

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Pressure and density

• Pressure is linked closely with density
• Pressure Force/Area
• Force is due to the collision of air molecules in
  their random motions. Air that is more dense (has
  more molecules in a given volume) will therefore
  exert more pressure than air that is less dense
• Mathematical relationship between density and
  pressure
• Pressure R x Density x Temperature
• ? What happens to pressure if density is halved
  while temperature remains constant?
• As stated earlier, density decreases with height
  since gravity keeps most of the mass near the
  earths surface. Therefore, what do you think
  happens to pressure as you go up in the
  atmosphere?

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Pressure changes with height
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Temperature changes with height

• Key point the suns rays pass (for the most
  part) through the atmosphere without transferring
  energy to the air
• The rays transfer their energy to the earths
  surface, and therefore heat the surface of the
  earth
• The earths surface then heats the atmosphere
  from below
• Therefore, temperatures are warmest near the
  surface and generally decrease with height (with
  2 exceptions)
• There are four distinct layers where temperature
  is either increasing or decreasing

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Atmospheric layers

• Outer Space
• Thermosphere Temperature increases with height
  due to the absorption of ultraviolet radiation by
  oxygen molecules
• -----------------------------------Stratopause
• Mesosphere Temperature decreases with height
• -----------------------------------Stratopause
• Stratosphere Temperature increases with height
  due to the absorption of ultraviolet radiation by
  ozone molecules (Very stable layer)
• --------------Tropopause-temperatures start
  increasing with height-----------------
• Troposphere Temperature decreases with height
• ------------------------------------
• Earths Surface Heats the air

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Vertical temperature profile
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Lapse Rate

• The lapse rate is defined as the change of
  temperature with height
• Negative lapse rate temperatures decrease as you
  go up (unstable)
• Positive lapse rate temperatures increase as you
  go up (stable)
• Average lapse rate in the troposphere
• -6.5 C/km (Temperature decreases 6.5 C every
  kilometer you ascend)
• The actual lapse rate can differ significantly
  from the average for thin layers of the
  troposphere, but typically if you take the
  average lapse rate for the entire troposphere it
  will be about -6.5
• The actual lapse rate is measure by radiosondes,
  which is a package of instruments that is
  attached to a balloon and takes measurements as
  it goes up.
• Sometimes there are layers in the troposphere
  where temperature increases with height these
  layers are called inversion layers

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Calculating lapse rates

• Lapse Rate
• Change in temp/ Change in height
• Example Given the following heights and temps,
  compute the lapse rate
• 25 C at 914 m
• 23.8 C at 270 m
• Lapse rate (25 C -23.8 C)/(914m-270m)
• 1.2 C / 644 m
• 1.86 C / Km
• (look at examples on page 4)

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Overall key points for those of you sleeping

• Pressure and density decrease non-linearly with
  increasing height since gravity keeps most of the
  atmospheres mass near the earths surface
• Temperature decreases, increases, decreases, then
  increases and the atmosphere is divided into
  layers based on the temperature changes
• weather occurs in the troposphere so
  meteorologists really dont care about the other
  layers
• Lapse rate is the change of temperature with
  height, and in the troposphere is usually -6.5 C
  / km
• The average lapse rate can be greatly different
  than -6.5, and these differences are very
  important in determining what type of weather
  is/will occur at a location

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