Model for surface packing and aeolian transport on sand ripples

Measurements indicate that the solid volume fraction on a sand ripple varies from random jammed packing at troughs to the minimum stable packing at crests. By relating variations of the solid volume fraction to those of the surface turbulent shear stress, a collisional model of reptation suggests a qualitative origin for these observations. Although the model overestimates the critical shear velocity at which reptation arises, it predicts the rate of aeolian transport on Earth and Mars.