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15.pdf
1. Space Environment
Lecture 15 – Geospace Climate
Solar and terrestrial drivers
Professor Hugh Lewis
SESA3038 Space Environment
2. Overview of lectures 15 & 16
• In the next two lectures we will look two key drivers of geospace climate
change:
– Solar activity, especially solar extreme ultra violet
– Terrestrial/anthropogenic greenhouse gas emissions
• We will explain how these change the temperature and the atmospheric
density in the thermosphere
• We will see what satellite measurements and model-based predictions
reveal about the long-term trends in density in the thermosphere
Space Environment – Geospace Climate
5. Solar drivers: EUV
5
Highly energetic
solar photons
Atmospheric density
change
Absorption in the
upper atmosphere
Space Environment – Geospace Climate
6. Solar irradiance (reminder)
Extreme Ultraviolet (EUV):
• Solar EUV irradiance varies over the 11-year solar cycle by factors of two to ten
https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2010JA015901
Space Environment – Geospace Climate
7. Solar drivers: EUV (reminder)
Solar EUV levels will vary over long timescales too:
http://cc.oulu.fi/~usoskin/personal/nature02995.pdf
Reconstructed sunspot number
Observed sunspot number since 1950
Space Environment – Geospace Climate
8. Solar drivers: EUV
Atmospheric density
change
Absorption in the
upper atmosphere
Absorption by
molecular oxygen
Atomic
oxygen
Highly energetic
solar photons
Space Environment – Geospace Climate
9. Atomic Oxygen (reminder)
• AO flux is two orders of
magnitude higher at solar
maximum compared with
minimum
• Energetic collision between
atomic oxygen and spacecraft
leads to the oxidation and
erosion of polymeric surfaces
• Most of the energy comes from the
velocity of the spacecraft
• AO also plays a role in geospace
climate change* Density of the LEO environment particles as a
function of altitude for one year mission length
during mean solar activity
Space Environment – Geospace Climate
12. Terrestrial drivers: GHGs
Atomic
oxygen
Carbon
dioxide
Infrared
radiation
• In the lower parts of the
atmosphere the IR radiation
would remain trapped (leading to
warming)
• In the upper atmosphere, the
mean free path length is large so
the IR radiation escapes into
space (leading to cooling)
Space Environment – Geospace Climate
13. Why temperature matters (reminder)
Kinetic energy is proportional to temperature:
k = Boltzmann constant, T = temperature, m = molecular mass, v = speed
Decreasing temperature (e.g. due to interaction of AO with CO2) leads to lower speeds
In free molecular flow regime this causes atmosphere to contract, as particles with lower energies
cannot reach higher altitudes
Upper layers of the atmosphere also cool due to conduction but also “pancake”
downwards leading to a reduction in atmospheric density at all orbital altitudes
3
2
𝑘𝑘𝑘𝑘 =
1
2
𝑚𝑚𝑣𝑣2
Space Environment – Geospace Climate
14. Solar & terrestrial drivers
Highly energetic
solar photons
Long-term
atmospheric
density change
Absorption
in the upper
atmosphere
Absorption
by molecular
oxygen
Atomic
oxygen
Carbon
dioxide
Infrared
radiation
Space Environment – Geospace Climate
15. Quick recap of lecture 15
CO2 cooling:
• Collisions between CO2 and O+
cause infrared emission to space in
Mesosphere & Lower Thermosphere
• Conduction causes cooling in upper
Thermosphere
• Maximum effect at solar minimum,
higher altitudes
Space Environment – Geospace Climate
16. Activities
• You can find the book chapter “Climate
Change in the Upper Atmosphere” by
Ingrid Cnossen in the “Course
Contents” folder on the Blackboard site
• There is also a fundamental article
(quite technical!) by Akmaev and
Fomichev explaining the terrestrial
drivers
Space Environment – Space Weather
