Abstract
An idealized morphodynamic model is constructed for formation of the aeolian sand ripples from small bottom perturbations of a two-dimensional sand bed. The main goal of the analysis is to evaluate the influence of the gravity flow (including “impact-induced gravity flow” in the reptation flux and “topography-induced gravity flow” in the creep flux) on the formation of the aeolian sand ripples and to clarify the relative contribution of various factors to the bed instability. A 3D linear stability analysis reveals that gravity flow appreciably affects the dynamics behaviors of aeolian sand ripples, which decreases the growth rate of sand ripples, tends to stabilize the sand bed, and leads to longer wavelength. We found that the competition between the destabilizing effect of reptation flow and the stabilizing effects of gravity flow leads to pattern selection. The along-crest diffusion of topography driven by impact and gravity is beneficial to the transverse stability of sand ripples, producing sand ripples with straighter and more continuous crests. For moderate values of D, the most unstable mode has zero value of the transverse wavenumber (ky = 0), thus corresponding to aeolian ripples with crests perpendicular to the wind. Moreover, when the impact angle is 9–16°, it has little effect on the characteristics of sand ripples for the initial stage of ripple development. For every increase of the impact angle by 1°, the initial wavelength only increases by about 1.5%. In conclusion, the influence of the gravity flow on the dynamics of sand ripples formation stage cannot be neglected.
Highlights
The main goal of the analysis is to evaluate influence of the gravity flow on the formation of the aeolian sand ripples and to clarify the relative contribution of various factors to the bed instability
We propose an ideal systematically investigate influence of the gravity flow on theflow formation the aeolian model to systematically investigate influence of the gravity on theofformation ofsand the ripples, to discuss the lateral stability of sand ripples and to clarify the relative contribution aeolian sand ripples, to discuss the lateral stability of sand ripples and to clarify the relative contribution of various factors to the bed instability; this is rarely seen in the existing theoretical model
We have developed a new idealized 3D aeolian sand ripples model that is able to systematically investigate gravity flow and other factors related to processes in aeolian ripples dynamics in the formation stage
Summary
Aeolian sand ripples are dynamic small-scale regular bedforms observed in sandy environments on Earth and other planets [1,2,3]. They are periodic morphological patterns with wavelengths ranging from a few centimeters to dozens of centimeters and heights of less than 1 cm, the profile of sand ripples is asymmetric. Aeolian sand ripples migrate, with their crests almost perpendicular to the prevailing wind direction, at a typical rate of about tens of millimeters per minute [4]. Predicting the behavior of aeolian sand ripples has practical interest because they tend to destroy farmland and cause desertification [5]
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