Orbital forcing as a driver of Titan's dune orientations
George D McDonald
PhD Candidate in Planetary Science, Georgia Tech
Aeolian dunes provide a historical record of Titan's equatorial climate. A surprising inference from observations by the Cassini mission is that the dunes appear to propagate in the direction opposite to the easterly flow predicted to dominate by general circulation models (GCMs).
What may help to explain this contradiction is that GCMs typically consider the circulation for present-day solar insolation conditions, while large linear dunes are constructed from and oriented by the integrated winds over tens of thousands of years. Thus, effects on the wind regime with duty cycles comparable to the reorientation timescales of the dunes need to be considered if circulation models are expected to produce winds that match those indicated by the dunes. In the case of Titan, Saturn's orbit undergoes apsidal precessions over a 45 thousand year cycle. I will discuss morphologic evidence that the dunes are in disequilibrium with the current wind regime and in turn may represent wind conditions from a previous orbital epoch. I will also present the first simulations of Titan's equatorial wind regime under orbital forcing, using 3 different Titan GCMs, with the result that the orbital configuration affects Titan's climate, and in turn dune orientations, across all models.
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