Other
Scientific paper
May 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995icar..115..126c&link_type=abstract
Icarus (ISSN 0019-1035), vol. 115, no. 1, p. 126-140
Other
107
Infrared Spectra, Latitude, Stratosphere, Temperature Gradients, Titan, Abundance, Astronomical Models, Hydrocarbons, Infrared Spectrometers, Nitriles, Radiative Transfer, Temperature Profiles, Voyager 1 Spacecraft
Scientific paper
We have analyzed nine Voyager 1 infrared spectral averages covering Titan's disk from 53 deg S to 70 deg N. By use of radiative transfer modeling we have determined the thermal profiles and mean molecular abundances in the stratosphere of the species with signatures in the region 200-1500/cm. Temperature latitudinal variations were found in accordance with Flasar and Conrath (1990). A maximal temperature decrease of 17 K at the 0.4-mbar level (225 km of altitude) is observed between 5 deg S (the warmest region) and 70 deg N, whereas the temperature drops only by approximately 3 K from 5 deg to 53 deg S. Mean molecular fractions, associated with atmospheric levels between 4 and 9 mbar, were derived from the best fit of the infrared data. The CO2 abundance remains constant from pole to pole within error bars. HCN shows a steady increase from south to north (total enhancement of greater than 30). For all the other molecules, variations in composition exist mainly between the equator and the north polar region. Ethane, acetylene, and propane show a moderate enrichment by about a factor of two. C4H2, C2H4, C3H4 show significantly higher mole fractions at latitudes greater than 50 deg N (by factors of approximately 7-15). C2N2 and HC3N, undetected southward of 50 deg N, show at least an order of magnitude enhancement near the north pole. The stratospheric haze opacity at wavenumbers larger than 600/cm was found to show a north-to-south enhancement of approximately 2.5 +/- 0.3. Coldest temperatures, found at high northern latitudes, are associated with enhanced gas concentration and haze opacity, and this may be caused by more efficient radiative cooling (Bezard, B., A. Coustenis, and C. P. McKay 1995). The observed latitudinal variations in hydrocarbons and nitriles may be related to seasonal and spatial variations of the solar flux (Yung, Y. L. 1987). The present results set constraints for the future development of 2-D seasonal photochemical models.
Bezard Bruno
Coustenis Athena
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