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ICARUS 74, 424--445 (1988) Methane Photochemistry and Haze Production on Neptune

Summary: ICARUS 74, 424--445 (1988)
Methane Photochemistry and Haze Production on Neptune
Mail Code 693.2, NASA Goddard Space Flight Center, Greenbelt, Map~yland20771
Department of Atmospheric and Oceanic' Science, The University of Michigan, Ann Arbor, Miehigan 48109
Received August 5, 1987; revised November 30, 1987
A numerical model was used to study methane photochemistry in the stratosphere of
Neptune. The observed mixing ratio of methane, 2%, forces photolysis to occur near the
CH4 homopause. For an assumed nominal value of the eddy mixing coefficient of 106 cm 2
sec-1 at the CH4 homopause, the predicted average mixing ratios of CzH6 and C2Hz, 1.5
x 10-6 and 6 x 10-7, respectively, agree well with observations in the infrared. The
acetylene and ethane abundances are weakly dependent upon the strength of the eddy
mixing and directly proportional to it. Haze production from methane photochemistry
results from the formation of hydrocarbon ices and polyacetylenes. The calculated mixing
ratios of C2H6, C2H2, and C4H2 are large enough to cause condensation to their respective
ices near the tropopause. These hazes are capable of providing the necessary aerosol
optical depth at the appropriate pressure levels required by observations of Neptune in
the visible and near IR. Polyacetylene formation from C2H2photolysis is limited by the


Source: Atreya, Sushil - Department of Atmospheric, Oceanic and Space Science, University of Michigan


Collections: Physics