Meridional Variations of Acetylene and Ethane On Jupiter

Details Meridional Variations of Acetylene and Ethane On Jupiter Meridional Variations of Acetylene and Ethane On Jupiter

Aug 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005dps....37.2202n&link_type=abstract

American Astronomical Society, DPS meeting #37, #22.02; Bulletin of the American Astronomical Society, Vol. 37, p.661

Astronomy and Astrophysics

Astronomy

Scientific paper

Hydrocarbons such as acetylene (C2H2) and ethane (C2H6) are important tracers in Jupiter's atmosphere, constraining our models of the chemical and dynamical processes. However, our knowledge of the vertical and meridional variations of their abundances has remained sparse. During the flyby of the Cassini spacecraft in December 2000, the Composite Infrared Spectrometer (CIRS) instrument was used to map the spatial variation of emissions from 10--1400 cm-1 (1000--7 μ m).
We have analyzed a zonally-averaged set of CIRS spectra taken at the highest (0.5 cm-1) resolution, to infer atmospheric temperatures in the stratosphere at 0.5--20 mbar via the ν 4 band of CH4, and in the troposphere at 150--400 mbar, via the H2 absorption at 600--800 cm-1 . Simultaneously, we retrieve the abundances of C2H2 and C2H6 via the ν 5 and ν 9 bands respectively. We find that the column abundance of C2H2 decreases sharply towards the poles by a factor ˜4, while C2H6\ is unchanged in the north and increasing in the south, by a factor ˜1.8.
An explanation for the meridional trends is proposed in terms of a combination of photochemistry and dynamics. Poleward, the decreasing UV flux is predicted to decrease the abundances of C2H2 and C2H6 by factors 2.7 and 3.5 respectively at a latitude 70o. However, the lifetime of C2H6\ in the stratosphere (5×109 s) is much longer than the dynamical timescale for meridional motions inferred from SL-9 debris (5×108 s), and therefore the constant or rising abundance towards high latitudes likely indicates that meridional mixing dominates over photochemical effects. For C2H2, the opposite occurs, with the relatively short photochemical lifetime (3×107 s), compared to meridional mixing times, ensuring that the expected photochemical trends are visible.

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