Grain-size characteristics of wind ripples on a desert seif dune

Megaripples are characterized by an armored layer of coarse sand covering the windward slope, which thus makes up the trimodal distribution of megaripple sand. Ripples, however, are composed of unimodal sand and lack an armored surfaced. It seems that, more than anything else, it is the process of sand grain sorting that affects the wavelength of the ripples and megaripples. -from Author