Morphologic and computational fluid dynamic analysis of sand dune-topographic obstacle interactions on Earth and Titan
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Earth and Titan have vastly different physical environments, but similar landscapes. Sand dunes, like those found in Earth’s deserts, cover large areas of Titan’s equatorial region and are important records of climate. Titan’s linear dunes and their interaction with topographic obstacles within the dune fields are thought to indicate westerly wind flow, which is opposite the easterly flow expected based on the spin of Titan and predicted from several global climate models (GCMs). The westerly interpretation of wind direction is largely based on the notion that the dunes represent streamlines that flow around the obstacles. However, the mechanics of how sand dunes are deflected around an obstacle is poorly understood. We examine the interactions between linear dunes and topographic obstacles by mapping the morphology of the obstacles and nearby dunes and using computational fluid dynamic (CFD) analysis of wind flow near obstacles. We map dune crest line orientation, obstacles, and other morphologies using visible satellite imagery for Earth and Cassini radar imagery for Titan. Obstacles length, width and height are mapped from both satellite imagery and digital terrain models (DTMs). We input obstacle topography and GCM and weather station data into WindNinja 2.2.0, a simple CFD. We use the CFD model to estimate wind velocity and direction near the obstacles, calculate gross bedform normal transport, and determine dune orientations around the obstacles. Our results indicate greatest variations in wind velocity and direction for regions within 500 meters of the obstacle and uniform wind flow patterns outside this zone. The modeled dune orientations also deviate greatest from the mean regional orientations in the upwind side of the obstacle. Topographically, the upwind side is higher than the downwind side, which could be a topographic signature of transport direction. These observations are consistent on both Earth and Titan. Identifying how dune patterns and topographic signatures of sand transport are affected by wind interactions with obstacles on Titan provides a new basis to evaluate wind directions on Titan.
Cisneros, Julia (2015). Morphologic and computational fluid dynamic analysis of sand dune-topographic obstacle interactions on Earth and Titan. Honors and Undergraduate Research. Available electronically from