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Mars' Atmosphere

Geography 441/541 S/18 Dr. Christine M. Rodrigue. Mars' Atmosphere. Mars' Atmosphere. Mars' atmosphere, weather, and climate Mars' atmosphere: Chemical composition and dustiness Vertical temperature and pressure structure Horizontal pressure structure Winds and the global circulation

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Mars' Atmosphere

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  1. Geography 441/541 S/18 Dr. Christine M. Rodrigue Mars' Atmosphere C.M. Rodrigue, 2018 Geography, CSULB

  2. C.M. Rodrigue, 2018 Geography, CSULB Mars' Atmosphere • Mars' atmosphere, weather, and climate • Mars' atmosphere: • Chemical composition and dustiness • Vertical temperature and pressure structure • Horizontal pressure structure • Winds and the global circulation • Martian weather: • Seasonality • Storms • Mars climate: • Geochemical cycles and weather • Climate zones • Climate change

  3. Mars' Atmosphere • Atmospheric gas composition: • Earth dominated by • Molecular nitrogen (78%) • Molecular oxygen (21%) • Variable amounts of water • Trace amounts of carbon dioxide (0.04%), argon (0.93%), various others • Mars dominated by • Carbon dioxide (95%) • Molecular nitrogen (2.7%) • Argon (1.6%) • Trace amounts of oxygen, carbon monoxide, water vapor, hydrogen C.M. Rodrigue, 2018 Geography, CSULB

  4. Mars' Atmosphere • Atmospheric density (p) and altitude (A): • Declines with altitude, as on Earth • Less atmosphere above compressing air • Mars lapse is less steep than Earth's • p = 0.699 * e -0.00009 * A (Mars) vs. p = 101.325 * e -0.00012 * A (Earth) • p (kPa); A (m) C.M. Rodrigue, 2018 Geography, CSULB

  5. Mars' Atmosphere • Vertical temperature structure • Temperature behavior with altitude defines bands, as on Earth • Less atmosphere above compressing air C.M. Rodrigue, 2018 Geography, CSULB

  6. Mars' Atmosphere • Hadley cell: • O2 & NO glow • 1.27 μm emission (NIR) • ESA MEX OMEGA C.M. Rodrigue, 2018 Geography, CSULB

  7. Mars' Atmosphere • Spatial variations in air pressure: • Hadley circulation: temperature + Coriolis force (Wikipedia image) C.M. Rodrigue, 2018 Geography, CSULB

  8. Mars' Atmosphere • Spatial variations in air pressure: • Hadley circulation: temperature + Coriolis force • Uplift at equator → low pressure • Air subsides ~45° → higher pressure • Like Earth around equinoces: 2 cells • Unlike Earth around solstices: 1 big cell C.M. Rodrigue, 2018 Geography, CSULB

  9. Mars' Atmosphere • Spatial variations in air pressure: • Hadley circulation: temperature + Coriolis force • Uplift at equator → low pressure • Air subsides ~45° → higher pressure • Like Earth around equinoces: 2 cells • Unlike Earth around solstices: 1 big cell C.M. Rodrigue, 2018 Geography, CSULB

  10. Mars' Atmosphere • Spatial variations in air pressure: • Hadley circulation: temperature + Coriolis force • Equinox and solstice C.M. Rodrigue, 2018 Geography, CSULB

  11. Martian Weather • Temporal variations: Polar cyclones: • Resemble Earth polar hurricanes • Earth to right, Mars below C.M. Rodrigue, 2018 Geography, CSULB

  12. Martian Weather • Temporal variations: Air pressure changes • Diurnal patterns (Pathfinder) • Midday spike, sundown pit • Note odd peak around midnight and "wee hours" drop • Complex secondary pattern, with as many as 4 pits and peaks C.M. Rodrigue, 2018 Geography, CSULB

  13. Martian Weather • Temporal variations: Air pressure changes • Diurnal patterns • MRO Climate Sounder confirmed Pathfinder data • Found it is global • More pronounced away from equator • Thermal tide creates lows under late afternoon sun C.M. Rodrigue, 2018 Geography, CSULB

  14. Martian Weather • Temporal variations: Air pressure changes • Diurnal patterns (LMST=Local Mean Solar Time) • Thermal tide inverse relationship to pressure tide • These create local winds C.M. Rodrigue, 2018 Geography, CSULB

  15. Martian Weather • Temporal variations: Air pressure changes • Seasonal patterns • Annual cycles of pressure changes • Huge increase as South Polar ice cap sublimes and starts moving to North Pole • Reverse blip from smaller North Pole effect C.M. Rodrigue, 2018 Geography, CSULB

  16. Mars' Climates • Temporal variations: Length of seasons • Unequal (Earth's close to equal in length) • Mars' greater eccentricity C.M. Rodrigue, 2018 Geography, CSULB

  17. Mars' Climates • Temporal variations: Telling time on Mars • Way to keep track of seasons on Mars: Solar longitude) • Starts at Spring Equinox • Northern Hemisphere C.M. Rodrigue, 2018 Geography, CSULB

  18. Mars' Climates • Temporal variations: Thermal inertia • Some materials heat up/cool down quickly (like land surfaces on Earth) • Low specific heat/thermal inertia • This affects diurnal and seasonal temperature contrasts, pressure differences, and winds/breezes: land-and-sea breezes, monsoons • On Mars, high albedo regions (dusty) have low thermal inertia and function like "continents" or inland areas on Earth • Others heat up/cool slowly (like ocean/lake surfaces on Earth) • High specific heat/thermal inertia • On Mars, low albedo surfaces tend to have high thermal inertia and function like "water bodies" on Earth climatologically C.M. Rodrigue, 2018 Geography, CSULB

  19. Mars' Climates • Temporal variations in pressure and wind and spatial variations in albedo C.M. Rodrigue, 2018 Geography, CSULB

  20. Mars' Climates • Temporal variations in global circulation: S. summer C.M. Rodrigue, 2018 Geography, CSULB

  21. Mars' Climates • Temporal variations in global circulation: morning at SL 0° C.M. Rodrigue, 2018 Geography, CSULB

  22. Mars' Climates • Temporal variations in global circulation: afternoon at SL 0° C.M. Rodrigue, 2018 Geography, CSULB

  23. Mars' Climates • Temporal variations in global circulation: evening at SL 0° C.M. Rodrigue, 2018 Geography, CSULB

  24. Mars' Climates • Cloudiness: • Carbon dioxide and water vapor • Pathfinder below • Phoenix to right C.M. Rodrigue, 2018 Geography, CSULB

  25. Mars' Climates • Storms: • Dust storms (Hubble) and dust devils • (Spirit in Gusev Crater) C.M. Rodrigue, 2018 Geography, CSULB

  26. Mars' Climate Change • Polar ice cap accelerated sublimation C.M. Rodrigue, 2018 Geography, CSULB

  27. Mars' Climates • Water and nitrogen cycle: • Triple point • 15N vs. 14N ratio high • Mars lost 90% of its N • Imagining it all back in the atmosphere, we get air pressure ~78 hPa • That would have allowed liquid water • Similarly, deuterium to hydrogen ratio high, ~7-8 x as high as Earth's • Mars must have lost 6.5 times as much water as there is in the modern ice caps! C.M. Rodrigue, 2018 Geography, CSULB

  28. Mars' Climates • Argon: • Change in isotope ratios found by MAVEN • 38Ar vs. 36Ar ratio high • The lighter isotope is more easily sputtered off at the top of the atmosphere than the heavier isotope • Mars lost 65% of its Ar • Reïnforces magnitude of atmospheric loss the way N and H isotopes do C.M. Rodrigue, 2018 Geography, CSULB

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