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J. R. Dire (U.S. Coast Guard Academy)
Dire (2000. Icarus 145, 428-444) developed a simple 2-D photochemical transport model for the stratosphere of Titan. The model contains 117 photolysis, chemical and condensation reactions for 22 hydrocarbon species along with atomic and molecular hydrogen. Transformed Eulerian mean equations are used to determine the meridional circulation. Mechanical forcing is modeled using eddy and Rayleigh friction, while thermal forcing is provided by Newtonian and eddy heating. The method of conservation of second-order moments is used for the meridional and vertical advection calculations. The model results are compared to the Voyager IRAS calculations performed by Coustenis and Bézard (1995. Icarus 115, 126-140). The model shows methane is well mixed in Titan's stratosphere. Model mixing ratios for ethane and propane agree well with Voyager IRIS data, however the model overestimates the abundances of acetylene and diacetylene. The model abundance for methylacetylene is within the Voyager observational uncertainty, but the abundance for mid-southern latitudes is at the high end of this uncertainty. The model does not accurately reproduce the observed ethylene abundances. Mid-latitude column densities (above 5 mbar) for ethane, propane, acetylene and methylacetylene vary seasonal by 10 respectively. Large seasonal variations for short lived chemical species results in significant seasonal variations in the chemical production rates for organic polymers at middle and high latitudes.