L15GH09Terrestrial_atmospheres

L15GH09Terrestrial_a - Terrestrial atmospheres atmospheric structure composition origin Text reading Chapter 11 esp pp 317-338 March 5 2009

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March 5, 2009 terrestrial atmospheres Terrestrial atmospheres •atmospheric structure, composition, origin •Text reading: Chapter 11: esp. pp 317-338
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March 5, 2009 terrestrial atmospheres Overview • Most of the planets, and three large moons (Io, Titan and Triton), have atmospheres Mars Very thin Mostly CO 2 •S o m e N 2 , Ar Winds, dust storms Venus Very thick Mostly CO 2 o m e N 2 Sulfuric acid clouds Earth •M o s t l y N 2 , O 2 o m e H 2 0, Ar Only 0.03% CO 2 . •W a t e r c l o u d s
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March 5, 2009 terrestrial atmospheres Secondary atmospheres • Can calculate how many volatiles had to be added to the atmosphere to get present surface conditions ¾ Not just current atmosphere content, but also the oceans and CO 2 locked up in rocks and shells. Gas Deep eruptions Continental geysers Required amount H 2 O 57.8 99.4 92.8 CO 2 23.5 0.33 5.1 Cl 2 0.1 0.12 1.7 N 2 5.7 0.05 0.24 S 2 12.6 0.03 0.13 Others <1 <1 <1 • Percent (by weight) added to atmosphere by volcanic outgassing
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March 5, 2009 terrestrial atmospheres Atmospheric compositions • Comparison of total volatile content on Venus, Earth and Mars shows better agreement. Volatile Venus Earth Mars H 2 O Atmosphere 60 3 0.02 Oceans/caps 0 250,000 5000? Crust 160,000? 30,000 10,000? Total 160,000? 280,000 15,000? CO 2 N 2 40 Ar Atmosphere 4 11 0.5 Atmosphere 2,000 2,000 300 Atmosphere 100,000 0.4 50 Oceans/caps 0 0 10 Crust 0 100,000 >900? Total 100,000 100,000 >1000? Table 11.2 : mass fraction of volatiles (x10 9 ).
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March 5, 2009 terrestrial atmospheres Physical Structure Use the equation of hydrostatic equilibrium to determine how the pressure and density change with altitude, in an isothermal atmosphere. You may neglect the change in gravitational force with altitude. ρρ g r GM dr dP = = 2
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March 5, 2009 terrestrial atmospheres Physical Structure • Pressure decreases with increasing altitude • Atmospheres are compressible, so density decreases with altitude • Compare with the pressure structure of the oceans, where the density remains approximately constant . atmosphere ocean
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March 5, 2009 terrestrial atmospheres Physical Structure •Surface temperatures and pressures are very different for the three terrestrial planets ¾ But the pressure scale heights are similar H z H z z e P e P P / 0 / ) ( 0 0 = = Venus Earth Mars T equil (K) 238 263 222 T surf (K) 733 288 215 P surf (bar) 92 1.013 0.0056 ρ surf (kg/m 3 ) 65 1.2 0.017 H(km) 16 8.5 18 pressure changes with altitude (z) can be written as (assuming g, T ~ constant over dz) where H is the “pressure scale height” - i.e characteristic height over which pressure decreases by a factor 1/e g m kT H H μ =
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March 5, 2009 terrestrial atmospheres Thermal structure
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This note was uploaded on 04/15/2009 for the course PHYS 275 taught by Professor Harris during the Winter '09 term at Waterloo.

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L15GH09Terrestrial_a - Terrestrial atmospheres atmospheric structure composition origin Text reading Chapter 11 esp pp 317-338 March 5 2009

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