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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.08.025 Byline: Brigette E. Hesman (a), Gary R. Davis (b), Henry E. Matthews (c), Glenn S. Orton (d) Keywords: Abundances; atmospheres; Neptune; atmosphere; Radiative transfer; Spectroscopy Abstract: The Ja=a3-2 rotational line of CO in Neptune has been measured using the heterodyne receiver B3 at the JCMT. The spectral resolution was 1.25 MHz and 25 tunings were used to cover a frequency range of almost 20 GHz. The measured line shape, encompassing both the broad absorption feature arising in the lower atmosphere and a narrow emission core from the upper stratosphere, indicates that the CO mole ratio is not uniform with altitude, with best-fit values of 2.2.sub.-0.4.sup.+0.6x10.sup.-6 in the upper stratosphere and 0.6[+ or -]0.4x10.sup.-6 in the lower stratosphere and troposphere. The higher stratospheric abundance indicates that a dual, internal and external, origin of CO is most likely. Author Affiliation: (a) University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5E2, Canada (b) Joint Astronomy Centre, 660 N. A'ohoku Place, University Park, Hilo, HI 96720, USA (c) National Research Council of Canada, HIA, Victoria, BC V9E 2E7, Canada (d) Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA Article History: Received 30 June 2005; Revised 29 August 2006

Abstract: Hydrocarbons in the upper atmosphere of Saturn are known, from Voyager, ground-based, and early Cassini results, to vary in emission intensity with latitude. Of particular interest is the marked increase in hydrocarbon line intensity near the south pole during southern summer, as the increased line intensity cannot be simply explained by the increased temperatures observed in that region since the variations between C2H2 and C2H6 emission in the south pole region are different. In order to measure the latitudinal variations of hydrocarbons in Saturn''s southern hemisphere we have used 3 cm−1 resolution Cassini CIRS data from 2006 and combined this with measurements from the ground in October 2006 at NASA''s IRTF using Celeste, an infrared high-resolution cryogenic grating spectrometer. These two data sets have been used to infer the molecular abundances of C2H2 and C2H6 across the southern hemisphere in the 1–10 mbar altitude region. We find that the latitudinal acetylene profile follows the yearly average mean daily insolation except at the southern pole where it peaks in abundance. Near the equator (5° S) the C2H2 abundance at the 1.2 mbar level is and it decreases by a factor of 2.7 from the equator toward the pole. However, at the pole (∼87° S) the C2H2 abundance jumps to , approximately the equatorial value. The C2H6 abundance near the equator at the 2 mbar level is and stays approximately constant until mid-latitudes where it increases gradually toward the pole, attaining a value of there. The increase in ethane toward the pole with the corresponding decrease in acetylene is consistent with southern hemisphere meridional winds [Greathouse, T.K., Lacy, J.H., Bézard, B., Moses, J.I., Griffith, C.A., Richter, M.J., 2005. Icarus 177, 18–31]. The localized increase in acetylene at the pole provides evidence that there is dynamical transport of hydrocarbons from the equator to the southern pole. [Copyright &y& Elsevier]