Aeolian Megaripples: Mathematical Model and Numerical Simulations

Aeolian sand ripples are a common feature on sandy deserts and beaches. Standard aeolian ripples have wavelengths of a few centimeters and amplitudes of a few millimeters. Sometimes, much larger ripples are observed. These are known by different names, such as ridges, granule ripples, gravel ripples, or megaripples. Aeolian megaripples are composed of a mixture of coarse and fine noncohesive material; a bimodal distribution of particle sizes is thought to be necessary for large, ripplelike bed forms to develop. Here, we discuss the extension of a recent model for the dynamics of aeolian megaripples. The model assumes that both the saltation and reptation fluxes are modulated by the emergent bed forms. We present a linear stability analysis of the full model as well as the results of numerical simulations. The modeled megaripples evolve through interactions between ripples of different sizes. The formation of megaripples is therefore another example of a self-organizing geomorphological system.