Mars Atmosphere Geography 441541 S18 Dr Christine M

Mars' Atmosphere Geography 441/541 S/18 Dr. Christine M. Rodrigue

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

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

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 (k. Pa); A (m)

Mars' Atmosphere • Vertical temperature structure – Temperature behavior with altitude defines bands, as on Earth – Less atmosphere above compressing air

Mars' Atmosphere • Hadley cell: – O 2 & NO glow – 1. 27 μm emission (NIR) – ESA MEX OMEGA

Mars' Atmosphere • Spatial variations in air pressure: – Hadley circulation: temperature + Coriolis force (Wikipedia image)

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

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

Mars' Atmosphere • Spatial variations in air pressure: – Hadley circulation: temperature + Coriolis force – Equinox and solstice

Martian Weather • Temporal variations: Polar cyclones: – Resemble Earth polar hurricanes – Earth to right, Mars below

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

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

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

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

Mars' Climates • Temporal variations: Length of seasons – Unequal (Earth's close to equal in length) – Mars' greater eccentricity

Mars' Climates • Temporal variations: Telling time on Mars – Way to keep track of seasons on Mars: Solar longitude) – Starts at Spring Equinox – Northern Hemisphere

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-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

Mars' Climates • Temporal variations in pressure and wind and spatial variations in albedo

Mars' Climates • Temporal variations in global circulation: S. summer

Mars' Climates • Temporal variations in global circulation: morning at SL 0°

Mars' Climates • Temporal variations in global circulation: afternoon at SL 0°

Mars' Climates • Temporal variations in global circulation: evening at SL 0°

Mars' Climates • Cloudiness: – Carbon dioxide and water vapor – Pathfinder below – Phoenix to right

Mars' Climates • Storms: – Dust storms (Hubble) and dust devils – (Spirit in Gusev Crater)

Mars' Climate Change • Polar ice cap accelerated sublimation

Mars' Climates • Water and nitrogen cycle: – Triple point – 15 N vs. 14 N ratio high – Mars lost 90% of its N – Imagining it all back in the atmosphere, we get air pressure ~78 h. Pa – 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!

Mars' Climates • Argon: – Change in isotope ratios found by MAVEN – 38 Ar vs. 36 Ar 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