浙江大学Pahtz Thomas、美国德州农工大学Durn Orencio等人近日的研究，揭示了地球上共同演化的空气动力和撞击波纹。2024年1月8日出版的《自然—地球科学》杂志发表了这项成果。
该团队研究人员报告了在环境空气和低压风洞中，细粒单分散沙层上可再现产生厘米和分米尺度的共同演化波纹，揭示了两个相邻的中尺度生长不稳定性。它们的形态特征和研究进行的定量颗粒尺度数值模拟，证实了较小的结构是撞击波纹，而较大的结构具有流体动力的起源。结果表明，比以前认为的要快，风成输送层必须在与平均跳跃长度相当的尺度上部分响应地形，但与推断的风成沙通量相对于风的相位滞后一致。
相应的流体动力学模型支持地球上空气动力学波纹的存在，将它们与巨型波纹和有争议的火星波纹联系起来。研究强调，本文成果为在太阳系中发现的中尺度颗粒底模提供了一个统一的视角。
据研究人员介绍，风成沙在地球、火星和其他行星上形成了多尺度的底模。根据传统观点，地球上十米尺度的沙丘和分米级的波纹是通过不同的机制形成的：湍流和地形之间相移相关的流体动力不稳定性，以及与地形和颗粒不稳定性相关的跳跃颗粒与地形的同步。
附：英文原文
Title: Coevolving aerodynamic and impact ripples on Earth
Author: Yizhaq, Hezi, Tholen, Katharina, Saban, Lior, Swet, Nitzan, Lester, Conner, Silvestro, Simone, Rasmussen, Keld R., Merrison, Jonathan P., Iversen, Jens J., Franzese, Gabriele, Kroy, Klaus, Pahtz, Thomas, Durn, Orencio, Katra, Itzhak
Issue&Volume: 2024-01-08
Abstract: Wind-blown sand creates multiscale bedforms on Earth, Mars and other planetary bodies. According to conventional wisdom, decametre-scale dunes and decimetre-scale ripples emerge via distinct mechanisms on Earth: a hydrodynamic instability related to a phase shift between the turbulent flow and the topography and a granular instability related to a synchronization of hopping grains with the topography. Here we report the reproducible creation of coevolving centimetre- and decimetre-scale ripples on fine-grained monodisperse sand beds in ambient air and low-pressure wind tunnels, revealing two adjacent mesoscale growth instabilities. Their morphological traits and our quantitative grain-scale numerical simulations authenticate the smaller structures as impact ripples but point at a hydrodynamic origin for the larger ones. This suggests that the aeolian transport layer would have to partially respond to the topography on a scale comparable to the average hop length, hence faster than previously thought, but consistent with the phase lag of the inferred aeolian sand flux relative to the wind. A corresponding hydrodynamic modelling supports the existence of aerodynamic ripples on Earth, connecting them to megaripples and to the debated Martian ripples. We thereby open a unified perspective for mesoscale granular bedforms found across the Solar System.
DOI: 10.1038/s41561-023-01348-3
Source: https://www.nature.com/articles/s41561-023-01348-3