Two-species continuum model for aeolian sand ripples

We formulate a continuum model for aeolian sand ripples consisting of two s pecies of grains: a lower layer of relatively immobile clusters, with an up per layer of highly mobile grains moving on top. We predict analytically th e ripple wavelength, initial ripple growth rate, and threshold saltation fl ux for ripple formation. Numerical simulations show the evolution of realis tic ripple profiles from initial surface roughness via ripple growth and me rger.