The shape of dunes

We present models to describe the dynamics of the surface of a dry granular bed, like a desert. These models, based on coupled differential equations can describe the formation and evolution of dunes. Field measurements have been performed to compare the numerical results. The concept of the Barchan dune as a soliton is disproved. We discuss in particular also the wind fie ld and the microscopic coupling with the sand grains. (C) 2000 Elsevier Sci ence B.V. All rights reserved.