Modeling the Formation of Sand Ripples: Gone with the Wind

Why does a wind blowing over a sandy surface establish ripples of uniform size, shape, and separation, rather than leveling the surface? Previous models, motivated by wind tunnel observations, have explained this by relying on the accumulation of saltating sand particles. Observing sand in its natural environment; however, indicates otherwise. Our model explains the formation of these ripples based only on reptating sand particles. The results of this model call into question the validity of these previous models.