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N.A. Teanby, P.G.J. Irwin, S.B. Calcutt, F.W. Taylor, N.E. Bowles (Oxford University), CIRS Team
On 2nd July 2004 Cassini's first fly-by of Titan occurred. The Composite InfraRed Spectrometer (CIRS) successfully returned thousands of infrared spectra. We have used this data to retrieve the spatial variation of HCN in Titan's stratosphere. Segments of the mid-IR spectrum, encompassing the HCN peak at 713cm-1, from 3cm-1 spectral resolution maps of Titan were used to retrieve the HCN abundance. Multiple spectra were averaged together, resulting in spectra that had a high signal to noise level, sufficient for this analysis. Contribution functions peak at around 10mbar, well into the stratosphere. The retrieved latitude-longitude map of HCN distribution shows an increase in abundance towards the north. The observed variation with longitude is much smaller, so large numbers of spectra have been averaged into latitude bins to obtain mean spectra with reduced noise. The retrieved HCN abundance is fairly constant with a volume mixing ratio of around 1.8x10-7 from 90S to 20S. More northerly latitudes indicate a steady increase, reaching 3.6x10-7 at around 10N, where the data coverage stops. This variation is consistent with previous measurements and may indicate transport of HCN produced at low latitudes to the Northern (Winter) pole.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.