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					An Introduction to the Upper
        Atmosphere

           Thomas Immel
      Space Sciences Laboratory
            UC Berkeley
Ionosphere
and Aurora
  What is important to know?
• Most importantly, you can’t understand
  the upper atmosphere without some
  understanding of what lies below. So we
  will look at the lower atmosphere.
• “Understanding” means a knowledge of
  conditions such as temperature, how it
  changes and why.
    Atmospheric Conditions
                 These three parameters and
• Temperature    how they vary with altitude
• Pressure       are some of the defining
                 characteristics of an
• Composition    atmosphere
    What controls these conditions?

• Physics       Solar Energy Input is an
                example of a process that
• Chemistry     involves both of these.
Solar Energy drives the whole
        atmosphere

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Solar Energy drives the whole
        atmosphere
                                         • It heats the Earths
                                           surface, driving winds
                                           and weather in the
                                           lower atmosphere

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       Solar Energy drives the whole
               atmosphere
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                                                                    surface, driving winds
                                                                    and weather in the
                              O2                                    lower atmosphere
                                                        N2
                                                                  • It deposits energy
                                                                    directly into the
O 2+                                     O+                         atmosphere which is
                               O                    +        N+     converted to heat and
                                               N2
                                                        N           chemical energy




                                         O2   N2
Solar Energy drives the whole
        atmosphere




•The 11-year solar cycle in sunspots is reflected in the
temperature and density in the upper atmosphere, as we
will see.
Solar Energy drives the whole
            thing

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•The 11-year solar cycle in sunspots is reflected in the
temperature and density in the upper atmosphere, as we
will see.
•Solar wind energy is converted into aurora, which also
adds heat to the upper atmosphere.
      A simple atmosphere
• Imagine a planet with a solid surface
  and no inputs from a sun. What do the
  pressure and temperature look like as a
  function of altitude?
• Let’s build a model to see what turns
  out.
 Build a model atmosphere

           Add a small layer of gas to
             Planet X. The pressure
             at the top of the layer is
Planet X     the same as space
             (zero). The pressure at
             the bottom depends on
             the weight of the gas
             you added.
               Build a model atmosphere

                               Pressure = 0
Height=1




                                                        Planet X



                                Pressure = 1


           At the top of the atmosphere, the pressure is zero, and at
              the bottom, lets define that as pressure=1
An atmosphere is made of gas

• Gasses obey a simple physical law.
Pressure is proportional to density and temperature.

Or, as pressure increases, so will the density and/or
temperature
                Build a model atmosphere


                          So let’s follow the rules.
Height=1




                            With the addition of the
                            second layer on top of
                            the first, the lower
                            layer will compress
  Height=0.75




                            and get hotter
                            (indicated with color)
                Build a model atmosphere
                    Pressure
                      0
Height=1




                               The pressure at the
                                bottom is still twice
                                the value in the
                      1         middle. But the
  Height=0.75




                                increase happens
                                over a shorter
                                distance.
                      2
Build a model atmosphere
    Pressure
    0




    1                 Planet X


    2

    3
           Keep going! Temperatures go up at
    4        the bottom as we add layers to
    5        the top. Pressure levels continue
    6        to get closer together.
Build a model atmosphere
            9                               9

            8                               8

            7                               7


 Altitude
            6                               6
            5                               5
            4                               4
            3
                                            3
            2
                                            2
            1
                                            1
            0
                                            0
                0   2      4   6   8   10
                                                0   2      4   6      8   10

                        Pressure
                                                        Temperature



            In a simple atmosphere, the pressures
            increase faster at the bottom, while the
            temperatures drop roughly linearly
            throughout. So, lets look at Earth’s
            atmosphere and see if our model works.
Earth’s lower and middle
      atmosphere
           The pressure drops very rapidly
           with increasing altitude, from
           about 1000 units at the surface
           to 1 at 45 km. And it just keeps
           dropping.

           The temperature drops regularly
           from the surface up to the
           “tropopause”, and then the
           atmosphere starts to heat up
           again!
Earth’s lower and middle
      atmosphere
           Reversals in the temperature
           trend defines the boundaries of
           the three regions of the
           atmosphere shown here.


            The huge departure from the
            temperature curve we
            expected from our simple
            model is due to stratospheric
            ozone. We forgot to include
            that. :)
Earth’s lower and middle
      atmosphere
           The upper atmosphere is
           usually considered to begin at
           the mesopause.



           There is a hint there, that the
           temperatures are again
           increasing with altitude.
                              Earth’s lower and middle
                        400

                                    atmosphere
                        300
Altitude (kilometers)




                        200


                                             Sure enough, the temperatures
                                             well exceed value reached
                        100
                                             below. That’s why the upper-
                                             atmosphere is called the
                                             thermosphere
                                 400   500     600      700     800   900   1000
                                             Temperature (Kº)
     The upper atmosphere
• Like the stratosphere, the temperatures
  in the thermosphere get hotter with
  altitude because of absorption of solar
  ultraviolet radiation.
• The difference is that ozone absorbs
  light that is just out of the visible range.
  The thermospheric gas absorbs
  extreme ultraviolet and X-rays.
         The upper atmosphere
           Sunspot cycle - Solar Visible Variation




•    The thermospheric gas absorbs extreme ultraviolet
    and X-rays. The sun is much more variable at these
    wavelengths over its 11-year sunspot cycle than it is
    in visible/near-UV wavelengths.
 The upper atmosphere
Sunspot cycle - Solar Extreme UV Variation

                                      • The thermospheric gas
                                        absorbs extreme
                                        ultraviolet and X-rays.
                                        The sun is much more
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                                        variable at these
                                        wavelengths over its 11-
                                        year sunspot cycle than it
                                        is in visible/near-UV
                                        wavelengths.
                        400




                        300
Altitude (kilometers)




                        200




                        100               The variation in Extreme ultraviolet radiation
                                          between solar minimum and solar maximum
                                          is so large that the temperature in the
                                          thermosphere vary by 100s of degrees
                              400   500      600      700     800   900    1000
                                           Temperature (Kº)
                        400




                        300
Altitude (kilometers)




                        200




                        100               The variation in Extreme ultraviolet radiation
                                          between solar minimum and solar maximum
                                          is so large that the temperature in the
                                          thermosphere vary by 100s of degrees
                              400   500      600      700     800   900    1000
                                           Temperature (Kº)
                        400
                                                With the huge increase in
                                                temperatures, you find
                                                that the pressure does not
                        300                     decrease so rapidly with
Altitude (kilometers)




                                                height, especially at solar
                                                maximum.
                        200




                        100




                              1e-5   1e-4      0.001   0.01   0.1   1   10   100   1000
                              Pressure (hPa)
  Who cares about the density
    of the thermosphere?
                                   March 23,
                                   2001
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     Mir Reentry
These guys care
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                  Feb ‘06 ISS altitude
                  344 km - Time for a
                  boost!
      Finally, Composition

Gas             Percent of
                Atmosphere
      Finally, Composition

Gas             Percent of
                Atmosphere
Nitrogen, N2
      Finally, Composition
Gas             Percent of
                Atmosphere
Nitrogen, N2    78%
      Finally, Composition

Gas             Percent of
                Atmosphere
Nitrogen, N2    78%

Oxygen, O2
      Finally, Composition

Gas             Percent of
                Atmosphere
Nitrogen, N2    78%

Oxygen, O2      21%
      Finally, Composition

Gas               Percent of
                  Atmosphere
Nitrogen, N2      78%

Oxygen, O2        21%

Carbon Dioxide,CO2 0.036% +0.0014%
                   per decade
                                    Finally, Composition
                        500           N2   O
                               O2
Altitude (kilometers)




                        400

                        300

                        200

                        100
                              Lower        Density   Higher
        In the thermosphere, the gas is thin enough that the separate species can
        separate out by mass. The proportions change dramatically with altitude.
        Atomic Oxygen dominates above 150-200 km.
                               Finally, Ion Composition
                        500
Altitude (kilometers)




                                      Nighttime        Daytime
                        400
                                                            O+
                        300

                        200

                                                  O+ NO+ N +
                        100                               2
                              Lower          Density      Higher

              The thermosphere is the source of all the plasma in the
              ionosphere. These region coexist, and interact strongly.
Studying the Upper Atmosphere
              Ultraviolet imagers in orbit can be
              used to observe composition
              changes in the thermosphere
              induced by auroral storms.
Noon




       Noon




                    Noon
Studying the Upper Atmosphere
Ultraviolet imagers in orbit can be used to quantify the
energy input to high latitudes that cause thermospheric and
ionospheric storms




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   Studying the Upper Atmosphere




The same ultraviolet
imagers can be used to
study the ionosphere. It is
actually very structured
and dynamic.
    Studying the Upper Atmosphere


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Solar Flare effects on the
upper atmosphere can also
be measured with orbiting
ultraviolet imagers.
Last Slide

				
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posted:3/22/2013
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