Atmospheric Structure

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• Atmospheric Structure

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The atmosphere

• The atmosphere is a thin blanket of gas that
  envelops the earth.
• The gases that make up the atmosphere are held
  close to the earth by the pull of gravity.
• With increasing distance from the earths
  surface, the temperature, density, and
  composition of the atmosphere gradually change
• On the basis of air temperature, the atmosphere
  can be divided vertically into four major layers.

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Atmospheric structure
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Troposphere

• The troposphere is the layer from the earths
  surface to the tropopause, which is at 10-15 km
  altitude depending on latitude and time of year.
  (Mt. Everest 8.85km)
• As altitude increases, air temperature decreases
  at a rate of about 3.5o per 1000 ft. The
  tropopause has a temperature of about 57oC.
• The lower part of the troposphere interacts
  directly with the surface of the earththis part
  of the troposphere is generally called air.
• The atmosphere in this layer is heated from below
  by convection and radiation from the earths
  surface.
• Most of our weather occurs in the troposphere.

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Stratosphere

• The stratosphere is the layer above the
  troposphere and extends to about 50km.
• The temperature rises with increasing altitude,
  reaching a maximum of about 1oC at the
  stratopause.
• The ozone layer is in the stratosphere. Ozone
  absorbs UV, causing the rising temperature with
  altitude in this layer.
• The temperature structure keeps the air calm in
  this layer. (Thats why jet aircraft fly in the
  lower stratosphere!)

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Mesosphere

• The mesosphere extends from the top of
  stratopause to 80 km.
• In the mesosphere, the temperature decreases with
  altitude.

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Thermosphere

• The layer of air above mesosphere is called
  thermosphere.
• In the thermosphere, temperature rises with
  altitude, caused by absorption of UV solar
  radiation by N2 and O2.

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The lower atmosphere

• The troposphere and the stratosphere together are
  called the lower atmosphere.
• The lower atmosphere account for 99.9 of total
  atmospheric mass
• The lower atmosphere is the domain of main
  interest from an environmental perspective.
• Ozone depletion (stratosphere)
• Air pollution (troposphere)

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Ionosphere

• Ionosphere is a region where ions and electrons
  are most abundant.
• This region is located at altitude above 60km,
  therefore lie within the mesosphere and above.

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Ionosphere

• Ionosphere acts as a conducting layer in the
  upper atmosphere that would allow a transmitted
  electromagnetic signal to be reflected back
  toward the Earth.

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Ionosphere Northern light (1)
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Ionosphere Northern light (2)

• Energetic events on the Sun can turn the solar
  wind into an intense solar "gale which injects
  large numbers of energetic particles in the
  Earth's magnetosphere.

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Ionosphere Northern light (3)

• The charged particles travel along the field
  lines with so much energy that they penetrate the
  ionosphere, where they hit gas atoms and
  molecules.
• These collisions give off energy that we see as
  colored light.

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atmospheric pressure

• The atmospheric pressure is the weight exerted
  by the overhead atmosphere on a unit area of
  surface

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Mass of the atmosphere

• Ps the global mean pressure at the surface,
  Ps9.84x104Pa.
• R6400 km, the earth radius
• g9.8m2/s, acceleration of gravity

Results ma 5.2x1018kg
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Pressure profile
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Barometric law

• Where Ma the molecular weight of air
• g acceleration of gravity
• R gas constant
• T temperature
• z altitude

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What fraction of total atmospheric mass is in the
troposphere?

• The troposphere contains all of the atmospheric
  mass except for the fraction P(tropopause)/P(surfa
  ce) that lie above the tropopause.

P(tropopause) 100 hPa P(surface)1000hPa Result
Ftrop 0.90
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Units for pressure

• International System of Units Pascal (N/m2)
• Hectopascal (hPa)
• mm Hg or Torr
• Millibar (mbar)
• psi (lb/in2)
• 1 atm 1.01325 x 105 Pascal (Pa) 1.01325 x
  103hPa
• 1 atm 760 mmHg 760 Torr
• 1 atm 1013.25 mbar
• 1 atm 14. 7 psi