Despite their ubiquity in present-day deserts and coastal regions, and despite their importance in the geological record and for the understanding of modern transport processes, no general theory exists for the complex interactions of wind and sand responsible for the formation of eolian ripples, and for the associated micro-stratigraphy. We propose to study this smallest class of eolian bedforms through simulations that directly extend prior analytical work. Ripples will be followed from birth to their mature, finite amplitude state, where the dispersion of velocities among waves forces interactions between ripples that result in the growth of the mean wavelength and decay of its standard deviation through time. Multiple grainsize systems will be addressed after an understanding of the monodisperse system is obtained. The resulting micro-stratigraphy will be tracked as it develops. Ripples will be modeled by cellular automation methods that have been shown to produce realistic bedform shapes and motion, and that physically mimic the motion of grains in actual ripples. The saltation impact events that drive ripple dynamics will be studied by simulation of individual impacts as well as by comparison with data on saltation collisions collected using high-speed photographic techniques. This latter work is being carried out at the University of Aberdeen by Dr. B.B. Willetts, with whom we have a N.A.T.O. travel collaboration grant. Additional constraints on the nature of ripple fields, both as they evolve and at steady state, will be derived using newly developed photographic techniques both in the wind tunnel and in local dunefields in southern California. Both the methods and the results of the proposed research should have a salutary effect upon the general field of sediment transport, including subaqueous systems.
