Role of CO2 Condensation in the Surface Environmental Evolution on Mars Part 1' Climate Transition B

1
Role of CO2 Condensationin the Surface
Environmental Evolution on Mars Part 1. Climate
Transition By Atmosphere-Ice Cap Mass Exchange

• ? Tokuta Yokohata
• National Institute for Environmental Studies
• yokohata.tokuta_at_nies.go.jp
• Masatsugu Odaka Hokkaido University
• Kiyoshi Kuramoto Hokkaido University

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The atmosphere can directly condense at the
surface and form CO2 ice caps.
Present Mars

• Very cold
• Solar radiation 0.44Earth
• Mean surface temp. -63 ?
• No liquid H2O
• Thin CO2 atmosphere
• Main component CO2 (95 )
• Atmospheric Pressure 6 hPa
• (0.06Earth)

3
Ancient Mars
A lot of fluvial morphologies
Warm climate occurred occasionally in the past?
Outflow Channels, 3-2 Ga
Valley Networks, 3.8 Ga
The warm climate might have achieved by the
strong greenhouse effect of the thick CO2
atmosphere
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What determines the atmospheric pressure?
K
Warm
B
CO2 atmosphere
Pole temp.
CO2 conden- sation temp.
Conden- sation
Evapo-ration
Cold
A
CO2 ice cap
Critical
Mckay et al 1991
Pole
1
10
102
103
Pressure hPa
5
What determines the atmospheric pressure?
K
Warm
B
CO2 atmosphere
Pole temp.
CO2 conden- sation temp.
Conden- sation
Evapo-ration
Cold
A
CO2 ice cap
Critical
Mckay et al 1991
Pole
1
10
102
103
Pressure hPa
6
What determines the atmospheric pressure?

• Trigger of climate transition
• Cooling
• CO2 loss due to the atmospheric escape or
  chemical weathering
• Warming
• Polar warming due to high obliquity or low
  albedo

• Previous works
• cannot explain occasional warming
• The ice cap mass is small corresponding to the
  critical pressure level.
• Even though the ice caps evaporate later, the
  pressure would not rise above a few 100 hPa.
• have never investigated the effect of H2O ice
• Liquid H2O must have frozen as climate cooling.
• High albedo of H2O ice would affect the climate
  states.

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What determines the atmospheric pressure?

• Trigger of climate transition
• Cooling
• CO2 loss due to the atmospheric escape or
  chemical weathering
• Warming
• Polar warming due to high obliquity or low
  albedo

• Previous works
• cannot explain occasional warming
• The ice cap mass is small corresponding to the
  critical pressure level.
• Even though the ice caps evaporate later, the
  pressure would not rise above a few 100 hPa.
• have never investigated the effect of H2O ice
• Liquid H2O must have frozen as climate cooling.
• High albedo of H2O ice would affect the climate
  states.

• The albedo effect of H2O ice
• may explain the occasional warming
• This has cooling effect, thereby the huge CO2 ice
  caps may form.
• The evaporation of the huge ice caps can cause
  high atmospheric pressure.

K
Warm
B
Pole temp.
CO2 conden- sation temp.
Cold
A
Critical
Mckay et al 1991
1
10
102
103
Pressure hPa
8
This Study

• Constructs a climate model with taking into
  account the H2O ice cover.
• Investigates the albedo effect of H2O ice on the
  climate stability.
• Simulates a climate transition.

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2-D Energy Balance Climate Model(Latitude-Vertica
l) Yokohata et al. 2002
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2-D Energy Balance Climate Model(Latitude-Vertica
l) Yokohata et al. 2002
IR Radiative-convective equilibrium model
of gray atmosphere Absorption coef. is
adopted from Pollack et al 1987
Solar
IR
Latent heat release of CO2 (Ts lt TCO2)
Horizontal advection
HA Eddy diffusion Model Diffusive
coefficient is proportional to the
pressure. This is based on the theory of
baloclinic instability (Stone 1962).
Atmosphere
Solar
IR
Sensible
CO2 Cap
CO2 Cap
H2O ice
H2O Ice
H2O Ice
CO2, H2O ice albedo 0.65 Regolith albedo 0.215
Surface
Pole
Pole
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2-D Energy Balance Climate Model(Latitude-Vertica
l) Yokohata et al. 2002

• Gives the solar radiation with seasonal
  variation.
• Gives H2O ice coverage region to be a parameter
• (Albedo of H2O ice 0.65, the same as that of
  CO2 ice).
• Solves the energy balance equation to find the
  evolution
• of energy fluxes and temperature distribution.

Solar
IR
Latent heat release of CO2 (Ts lt TCO2)
Horizontal advection
Atmosphere
Solar
IR
Sensible
CO2 Cap
CO2 Cap
H2O ice
H2O Ice
H2O Ice
CO2, H2O ice albedo 0.65 Regolith albedo 0.215
Surface
Pole
Pole
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Numerical Experiments

• Atmospheric pressure stability
• Pressure is fixed.
• Annual condensation-evaporation flux at the polar
  surface is calculated.
• Climate transition simulation
• Mass conservation of the atmosphere-ice cap
  system is explicitly solved.

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Pressure Stability (No H2O Ice)
Total annual CO2 evaporation 107 kg / Martian yr
Downward convex
Net conden- sation
Greenhouse effect and horizontal heat advection
to polar region increases.
CO2 condensation temperature increases.
Pressure hPa
1
10
102
103
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Pressure Stability (No H2O Ice)
Total annual CO2 evaporation 107 kg / Martian yr
Escape Weathering
Critical
Present
Net conden- sation
Collapse Condensation
Pressure hPa
1
10
102
103
15
Effect of H2O Ice Coverage
Total annual CO2 evaporation 107 kg / Matian yr
Critical
Critical
Critical
Evaporation decreases
40o
0o
Temperature at lower latitude decreases due to
high H2O ice albedo.
For larger H2O ice coverage, critical level
shifts to higher pressure
Horizontal heat advection to polar region
decreases.
Pressure hPa
1
10
102
103
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Critical Level Pressure H2O Ice vs.
ObliquitySolar constant 0.75
60
50
1 x 10
40
1 x 102
30
4 x 102 hPa
Obliquity Degree
2 x 103
20
1 x 103
2 x 103
10
0
20
40
100
60
80
H2O Ice Coverage
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High Obliquity (gt 45 degree) CO2 ice cap
evaporates owing to polar warming.
Critical Level Pressure Obliquity vs. H2O
IceSolar constant 0.75
60
Total annual evaporation is always zero
50
1 x 10
40
1 x 102
30
4 x 102 hPa
Obliquity Degree
2 x 103
20
1 x 103
2 x 103
10
Large H2O ice coverage (100 ), Low Obliquity (lt
10 degree) Critical level pressrure 2 x 103 hPa
0
20
40
100
60
80
H2O Ice Coverage
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Implications

• The albedo effect of H2O ice cover can cause the
  collapse condensation from higher pressure (2
  103 hPa).
• than previous works ( 102 hPa).
• This is favorable for occasional warming.
• The huge ice cap (formed by the collapse
  condensation) can evaporate by the obliquity
  increase (gt 45 degree).
• The higher pressure can be achieved again.

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Climate Transition SimulationSolar const. 0.75
Pressure hPa
Pressure hPa
103
Global H2O ice coverage, Present Obq.
102
No H2O ice Obq. 45 deg.
10
1
8
16
0
8
16
0
Time 100 yr
Time 100 yr
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Climate Transition SimulationSolar const. 0.75
Time scale for climate transition is 103 yr,
much shorter than the obliquity cycle ( 106 yr)
Pressure hPa
Pressure hPa
103
Global H2O ice coverage, Present Obq.
102
No H2O ice Obq. 45 deg.
10
1
8
16
0
8
16
0
Time 100 yr
Time 100 yr
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Summary

• By the albedo effect of H2O ice cover, the
  collapse condensation would occur from much
  higher pressure than previously assumed.
• The above feature is favorable for occasional
  climate warming, because the high atmospheric
  pressure could achieved again by the CO2 ice cap
  evaporation owing to the obliquity increase.
• Time scale for collapse condensation and ice cap
  evaporation would be short compared to obliquity
  cycle.

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????? ??????????????? ????????????? CO2 ????
??, 1997
24
??????????????
??, 1997
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CO2-H2O ??????

• ??(38???)
• CO2 ?? 1-4 ?? ?
• H2O 10-103 m (??????)
• ??
• CO2 ?? 6x10-3 ??
• H2O 10 m (??)
• 500 m ? (Max, ??)

???? ????
26
?????? ?????
27
CO2 ?????? ????
?? ??
?? ??
28
CO2 ????? (H2O ? ???)
??????????? 107 kg s-1
???
???? ????
??? ??? ??
??? Pa
29
CO2 ????? (CO2 ??????)
??????????? 107 kg s-1
??
???
??? ??
????????
??? Pa
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Collapse Condensation Solar const. 0.75,
global H2O ice coverage
Pressure hPa
Altitude km
0.9
103
20000
Huge CO2 cap forms.
Reduces to 1/500
16000
12000
102
Very short, as geological time scale
8000
0.5
4000 yr
10
Present
1
8
16
0
70
80
90
60
Time 100 yr
Latitude degree
31
???????? ???? 0.75, ?? H2O ?
??? Pa
?? 1 km
0.9
105
105 Pa (1 ??) ?? ??
?? CO2?? ??
104
0.5
103
??
102
8
16
0
70
80
90
60
?? 100 ?
?? ?
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Evaporation of CO2 Ice Caps Solar const. 0.75,
Obliquity 45 degree
Pressure hPa
Altitude km
0.9
103
Huge CO2 caps disappear.
300
102
0.5
Runaway Evaporation
500 yr
10
1
8
16
0
70
80
90
60
Time 100 yr
Latitude degree
33
???????? ???? 0.75, ?????? 0.45
??? Pa
?? 1 km
105
0.9
?? ?? ??
104
?? ??
0.5
103
102
8
16
0
70
80
90
60
?? 100 ?
?? ?