Dynamics of Aeolian Sand Heaps and Dunes: The Influence of the Wind Strength

Summary

The so-called minimal model provides an efficient minimum mathematical description of aeolian sand dune formation based on turbulent boundary layer calculations and a mean-field like saltation model. It allows us to analyze the effect of environmental conditions — uncontrollable in the field — on the characteristic shapes of dunes systematically. While the previously studied stationary solutions obtained under periodic boundary conditions are “unphysical” in the sense that they correspond to unstable fixed points of the equations, the solutions for open boundary conditions are shown to be strongly constrained by the unstable manifolds of these fixed points. For morphological evolution under periodically (e.g. seasonally) changing wind conditions a rule of thumb emerges, saying that the shapes of comparatively small/large dunes are slaved by the unstable manifolds pertaining to the actual/time-averaged environmental conditions, respectively.