Packing variations on a ripple of nearly monodisperse dry sand

Dielectric measurements reveal that bulk density on the surface of recently mobilized dry ripples of a nearly monodisperse desert sand varies from the random jammed packing at troughs to the minimum value for a stable packing at crests, suggesting that active ripples are relatively loose structures moving above a more consolidated substratum. Although the wind‐driven evolution of static pressure on the surface induces air seepage through sand, we show that such internal flow is not strong enough to swell the bed and explain variations of bulk density on the surface.