Download PHY2505 Lecture 5 - Earth, Atmospheric, and Planetary Physics

Atmospheric Radiation – Lecture 11
PHY2505 - Lecture 20
Comparative atmospheres:
Mars, Earth & Venus
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Atmospheric Radiation – Lecture 20
Comparative planetology
Comparative planetology is the name given to an approach to studying the
planets. This approach is based on the idea that the individual planets can
be better understood by comparing the physical processes of all the planets.
The basic physical ideas in our physical models for one planet must hold
true in general for the other planets.
Comparing the atmospheres of planets, particularly their thermal
structures, gives us insight into the processes that drive climate.
The terrestiral planets: Venus, Earth and Mars, formed at a similar time
under similar conditions and yet their climates vary dramatically. A question
is whether relatively small changes to the thermal structure in the Earth’s
atmosphere could push it into the climate regime of either of its nearest
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neighbours.
Atmospheric Radiation – Lecture 20
Effective temperature
Venus
Distance from Sun (A.U.)
0.72
S=Flux, W/m2
2643
r=Albedo
0.8
Effective Temperature, K
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Actual observed Temperature, K 730
http://solarsystem.colorado.edu/cu-astr/home/lowRes.html
Earth
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1370
0.3
255
288
Mars
1.52
593
0.22
212
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Atmospheric Radiation – Lecture 20
Greenhouse hypotheses
Primary atmospheres: the region of the solar nebula where
terrestrial planets were formed was too hot for the
condensation of volatiles such as CO2 or H2O.
These molecules either arrived
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as trace species, adsorbed on or captured in the interiors of
the solids that gradually accreted to form the planets, or
they were brought in by comets, from the region of the solar
system beyond the snow line.
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Atmospheric Radiation – Lecture 20
Water on planets
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Atmospheric Radiation – Lecture 20
Greenhouse hypotheses
VENUS
Temperature of Venus initially higher than Earth
Gases in atmosphere trap heat (greenhouse effect)
Any water on surface evaporates and adds to greenhouse gases
Subsequently water is broken down and H escapes
Temperature rises even more
Runaway greenhouse effect
EARTH
CO2 comparable to Venus but adsorbed in surface by way of Urey reactions
MARS
Gravity weaker than Earth, secondary atmosphere sustained
large losses through atmospheric escape
Reverse greenhouse effect: planet cold, water freezes reducing
greenhouse gases, freezes more, cools more until
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low pressure below the triple point of water
Atmospheric Radiation – Lecture 20
Venus current atmosphere
Composition
(near surface, by volume)
CO2 96.5%
N2 3.5%
Minor species (ppm)
SO2 - 150;
Argon (Ar) - 70;
Water (H2O) - 20;
Carbon Monoxide (CO) - 17;
Helium (He) - 12;
Neon (Ne) - 7
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Atmospheric Radiation – Lecture 20
Earth current atmosphere
Composition
Nitrogen 78.08%
Oxygen 20.95%
*Water 0 to 4%
Argon 0.93%
*Carbon Dioxide 0.0360%
Neon 0.0018%
Helium 0.0005%
*Methane 0.00017%
Hydrogen 0.00005%
*Nitrous Oxide 0.00003%
*Ozone 0.000004%
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Atmospheric Radiation – Lecture 20
Mars current atmosphere
Composition
Carbon Dioxide (CO2) - 95.32%
Nitrogen (N2) - 2.7%
Argon (Ar) - 1.6%
Oxygen (O2) - 0.13%
Carbon Monoxide (CO) - 0.08%
Minor (ppm):
Water (H2O) - 210
Nitrogen Oxide (NO) - 100
Neon (Ne) - 2.5
Krypton (Kr) - 0.3
Xenon (Xe) - 0.08
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Atmospheric Radiation – Lecture 20
State of current measurements
Current data
MARS
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Atmospheric Radiation – Lecture 20
Climate problems: Venus
Past climate:
Magellan mapping of surface suggests recent geological
activity: whole surface resurfaced 700M years ago – has
this produced climate change?
Current climate:
Is the current climate stable?
What governs formation of H2SO4 clouds?
Why are elevated winds so high?
Outgassing of SO2, CO2 reactions with surface, - is Venus
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cooling?
Atmospheric Radiation – Lecture 20
Climate modelling: Venus
Two-stream radiative–convective model
high-resolution spectral databases
chemical/microphysical model of Venus’ clouds
1. How do variations in atmospheric water and sulfur dioxide affect cloud
structure and planetary albedo? How do these, in turn, affect the
temperature at the surface?
2. How does the equilibration of atmospheric sulfur dioxide with surface
minerals affect cloud structure and surface temper-ature, and over what
timescales?
3. How have changes in atmospheric water abundance due to exospheric
escape of hydrogen and volcanic outgassing af-fected cloud structure and
surface temperature, and over what timescales?
4. What was the effect on Venus’ cloud structure and sur-facetemperature of an
epoch of rapid plains emplacement by widespread, global volcanism?
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Atmospheric Radiation – Lecture 20
Venus: results
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Atmospheric Radiation – Lecture 20
Venus: results
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Atmospheric Radiation – Lecture 20
Venus: results
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Atmospheric Radiation – Lecture 20
Climate problems: Mars
Water & faint young
sun paradox: definite
dramatic climate
change ~ 2Ga
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Atmospheric Radiation – Lecture 20
Climate problems: Mars
Global dust storms –
coupled feedbacks?
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Atmospheric Radiation – Lecture 20
Climate problems: Mars
Issues:
Past climate:
Producing enough CO2 to sustain liquid water
Currrent climate
Asymmetry of polar caps
Feedback due to cloud and dust
Orbital cycle
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Atmospheric Radiation – Lecture 20
Climate problems: Mars
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