美国杜克大学C. W. Lester团队揭示了由颗粒床冲击力学控制的风波纹的出现。该研究于2025年4月8日发表在《自然—地球科学》杂志上。

在地球上的河床、沙地和雪地沙漠以及其他行星环境中都观察到了周期性的沉积模式。最普遍的模式之一，熟悉的风或“冲击”涟漪，装饰着地球上的沙滩和干旱地区。尽管大气层较薄，但在火星上观测到的风成撞击涟漪与陆地上的涟漪大小相同，这引发了人们对其形成的质疑。

研究组在数值模拟中表明，冲击波纹的出现波长是由颗粒-床层冲击的力学控制的，而不是由床层上方颗粒的特征轨迹控制的。他们发现，输运中晶粒轨迹的分布基本上是无标度的，这需要临界点的接近，并排除了选择波纹波长的输运相关长度标度。相比之下，当颗粒撞击床层时，导致颗粒喷射的过程引入了一个集体颗粒长度尺度，该尺度决定了波纹的尺度。

研究组提出了一个理论模型，该模型预测了大多数行星条件下相对恒定的波纹大小。此外，该模型预测，对于金星等高密度大气，或者地球上足够大的沙粒，撞击涟漪会向上风传播。尽管需要风洞和现场实验来证实这种“反涟漪”的存在，但研究组建议，这种风吹沉积物输送定量模型可用于从撞击涟漪的大小和传播速度推断其他行星的地质和环境条件。

附：英文原文

Title: Emergence of wind ripples controlled by mechanics of grain–bed impacts

Author: Lester, C. W., Murray, A. B., Duran, Orencio, Andreotti, B., Claudin, P.

Issue&Volume: 2025-04-08

Abstract: Periodic sediment patterns have been observed on Earth in riverbeds and sand and snow deserts, but also in other planetary environments. One of the most ubiquitous patterns, familiar wind or ‘impact’ ripples, adorns sand beaches and arid regions on Earth. The observation of aeolian impact ripples on Mars the same size as their terrestrial counterparts despite a thinner atmosphere raises questions about their formation. Here we show in a numerical simulation that the emergent wavelength of impact ripples is controlled by the mechanics of grain–bed impacts and not the characteristic trajectories of grains above the bed. We find that the distribution of grain trajectories in transport is essentially scale-free, invoking the proximity of a critical point and precluding a transport-related length scale that selects ripple wavelengths. By contrast, when a grain strikes the bed, the process leading to grain ejections introduces a collective granular length scale that determines the scale of the ripples. We propose a theoretical model that predicts a relatively constant ripple size for most planetary conditions. In addition, our model predicts that for high-density atmospheres, such as on Venus, or for sufficiently large sand grains on Earth, impact ripples propagate upwind. Although wind-tunnel and field experiments are needed to confirm the existence of such ‘antiripples’, we suggest that our quantitative model of wind-blown sediment transport may be used to deduce geological and environmental conditions on other planets from the sizes and propagation speeds of impact ripples.

DOI: 10.1038/s41561-025-01672-w

Source: https://www.nature.com/articles/s41561-025-01672-w