COMPUTER-SIMULATIONS OF SELF-ORGANIZED WIND RIPPLE PATTERNS

A variety of surficial patterns including beach cusps, sand dunes, wind ripples, stone stripes and sorted circles have been reproduced successfully with computer simulations in which the patterns develop via self-organization and both transporting agents and transported material are discretized. As an example, three-dimensional, grain-level computer simulations of wind ripple formation are described. The results of these simulations demonstrate that a model that includes only incremental transport of surface grains by impacts from wind-propelled hopping (saltating) grains is sufficient to produce self-organized wind ripples whose size, cross-sectional shape, plan-view geometry and time evolution from an original hat surface fall within observed ranges for natural ripples. Simulated wind ripples are initiated from a flat sand bed because of an instability deriving from a dependence of transport rate on slope. A characteristic ripple spacing that is proportional to the grain diameter and increases slowly with time develops as a result of interactions and mergers between ripples. Imperfections to the ripple pattern play a significant role in the determination and evolution of the spacing of simulated ripples.