Relevance of fast westerlies at equinox for the eastward elongation of Titan’s dunes

Numerous linear dunes with eastward streamline pattern on Titan have mostly been interpreted as evidence of predominantly westerly (eastward) equatorial surface winds, although such winds are meteorologically hard to understand. Simulation with a general circulation model shows that the observed dune alignment nearly parallel to the equator maximizes the gross bedform-normal transport for seasonally reversing wind. Many dunes are found to be oblique or transverse to the resultant drift direction. The eastward streamline pattern of Titan’s dunes may be a result of occasional fast westerlies that elongate the dunes eastward. These winds are turbulent, and are predicted to occur during the equinoctial passage of the intertropical convergence zone. A large threshold speed for sand transport can preclude westward sand transport although the average equatorial surface wind is easterly. Global-scale topography is found to have little impact on the dune orientation.