Atmospheres. Take a weather class for details (870:021) But until then… Physical Principles Structure Characteristics Origin/Evolution. Hydrostatic Equilibrium P=change in pressure G=Constant M=planet mass z=height r =density. Ideal Gas Law =Constant T=Temperature (K)
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Atmospheres • Take a weather class for details (870:021) • But until then… • Physical Principles • Structure • Characteristics • Origin/Evolution
Hydrostatic Equilibrium P=change in pressure G=Constant M=planet mass z=height r=density Ideal Gas Law =Constant T=Temperature (K) m=mean molecular weight Atmospheric Physics
Combine them to get Pressure Scale Height (H) (height needed for pressure to drop e ) Assume isothermal atmosphere (good temperature assumption…?)
What influences the Temperature? • Sun • Internal energy sources – re-radiated light • Chemical reactions – change opacity • Clouds/haze – change opacity, latent heat • Volcanoes/Geysers • Oxidation/Sedimentation • Biogenic, Anthropogenic processes • Temperature structures not all the same
Localized temperature influences • Distance from Sun • Albedo • Angle of the Sun • Rotation rate • Non-blackbody aspects - emissivity
Solar heating – assuming sun over equator T = Surface temperature Fsun= Solar Constant (1360 W/m2) A = albedo f = latitude e = emissivity s = constant a = distance from Sun
Atmosphere Structures • Troposphere • Tropopause • Stratosphere • Statopause • Mesosphere • Mesopause • Thermosphere • Thermopause/Exobase • Exosphere
Wimpy Atmospheres • Mercury • O, Na, He, K, H, Ca, Xe, Kr, CO2, H2O, Ar • P=10-15 bar, T=100-700 K • Moon • H, He, Ar, Na, K • P=10-15 bar, T=120-380 K • Pluto – • N2, CO, CH4, ethane • P=6.5x10-6 – 2.4x10-5bar, T=53 K • Triton – • N2, CH4 • P=1.4x10-5bar, T=40 K • Io – SO2, SO • Enceladus – N, CO2, CH4
Atmospheric Motions • Circulation Patterns • Thermal Tidal Winds • Condensation Winds • Hadley Circulation • Pressure gradients • Rotation (Coriolis effect)
Origin • Where do atmospheres come from? • Why are they different? • Origins different (location) • Gravity - escape • Chemical reactions – Photodissociation/Recombination CH4 + H2O ↔ CO + 3H2 2NH3↔ N2 + 3H2 H2S + 2H2O ↔ SO2 + 3H2 Etc. • Plus Ar, Kr, Xe in solar amounts – NOT! • Outgassing
Earth’s Atmospheric History • Past was hotter • Early Greenhouse effect (H2O, CO2, CH4, NH3) • CO2 cycles through a system • Weathering • Carbonate minerals • Volcanism • Oxygen – life, dissociation of H2O
Mars Atmospheric History • Thicker in the past (Noachian era) • Atmosphere ~ 1 bar, T ~ 300 K • Rich in CO2, H2O • CO2 lost through • Weathering • Adsorption into regolith • Condensation • Impacts • No water, no CO2 cycling • No volcanism, no CO2 cycling • Why no water?
Venus Atmosphere History • Very little H2O – Why? • D/H ratio is high! • Lost to space? No… Runaway greenhouse! • Outgassing • more water in atmosphere • more green house effect • No CONDENSATION!