Atmospheres of Uranus and Neptune

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Atmospheres of Uranus and Neptune

• Sam Williams
• http//www.cs.berkeley.edu/samw/249/

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Energy

• Uranus
• Equator receives slightly less solar energy than
  poles
• Planet radiates slightly more energy than it
  receives (13)
• Significantly more energy emitted than absorbed
  at equator
• Neptune
• Equator receives about twice as much solar energy
  as the poles
• Planet radiates more than twice the energy it
  receives (internal heat source), and about the
  same as Uranus radiates.

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Appearance (Uranus)

• To the unaided eye, it appears uniform, but there
  are slight color variations
• Photochemical meteor/ring dust haze in
  stratosphere?

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Appearance (Uranus)

• In IR, features are more pronounced

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Appearance Neptune

• High altitude clouds

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Appearance (Neptune)

• Neptune shows color variation in bands
• Also, As season progresses, southern bands
  brighten (near IR)

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Composition

• Uranus
• 83 H2 15 He 2 CH4
• Neptune
• 79 H2 18 He 3 CH4
• Traces of N2, HCN, H2S, NH3, CO
• 30-40x solar ratio of CH

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Zonal Winds

• Far fewer bands than on Jupiter and Saturn
• Uranus -100m/s(10o), 0(-15o,30o), 175(-50o)
• Neptune -300m/s(0o), 0(50o), 225(75o)
• Less sunlight less turbulence flow less
  disturbed

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Temperature

• Tropopause 55K
• Stratosphere on Uranus is less than 75K until
  1mbar (cooler than Neptune), but more recent IR
  observations have shown a warming in the
  stratosphere.
• Methane, ethane, acetylene act as coolants in
  stratosphere, similar mesospheric temperature
  (150K)

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Processes

• Ethane (C2H6), ethylene (C2H4), acetylene (C2H2)
  from methane photodissociation.

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Processes

• Uranus micrometeorites bring CO and H2O to the
  stratosphere. (French group using VLTESO)
• Neptune N2 in stratosphere (accretion from
  Triton/rapid upward convection)

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Clouds

• methane ice (CH4) lt1bar
• (limit of probing)
• Probably have
• Methane droplets?
• hydrogen Sulfide (H2S) 2-5bar
• more H2S, so no NH3 clouds?
• NH4 hydrosulfide (NH4SH) 15-30bar
• water 15-50bar
• Solution Cloud to a few 100bar

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Great Dark Spot

• Comparable in size to GRS
• Storm? (1200mph, counterclockwise rotation,
  anticyclone)
• Below the tropopause
• Moved towards equator, dissipated, new one formed
  in the northern hemisphere

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Great Dark Spot

• Hole in the methane droplet cloud deck?
• Like the ozone hole over Antarctica?
• What would destroy methane in that spot?