Characterizing Mass-Flux Profiles in Aeolian Saltation Systems

被风吹来的颗粒重塑了地球上的许多景观；这些被称为风成过程，某些基本方面仍然未知。事实上，预测风沙运输速率是地貌学探索的关键，它可以为风对可侵蚀表面的改变（侵蚀、堆积和河床形态的形成）以及沿海和干旱沙丘系统的形成和演变建立确定性模型。在过去的三十年里，对风沙系统动力学的理解有了显著的提高。然而，利用基本环境信息，如风速和平均沙粒大小，以及与特定风成系统的关系来预测输沙率，仍然存在相当大的不满意。特别是，即使是最基本的输运系统，对于沙质表面上跳跃颗粒的特征分布也没有一致的看法。这是很重要的，因为运动颗粒的分布是对沙的总输运速率的基本控制。该项目旨在阐明自然环境中风沙垂直分布的独特特征。特别是，研究人员将通过收集和分析高质量的野外数据集来评估劳斯浓度剖面模型对风成跃变的适用性。根据颗粒大小和风切变速度的可识别特征，劳斯浓度剖面使垂直颗粒分布归一化，并已证明其在水动力系统中的实用性。研究人员假设风成跃迁的垂直分布符合劳斯剖面模式；劳斯参数修正了在不同环境条件下获得的质量通量分布之间的一些可变性；在野外测量的质量通量分布特征在统计上与在风洞实验中测量的特征不同。他们通过设计一个创新的、空间和时间上详细的实验来解决这个问题，该实验将测量近地面风和跃变场的垂直结构。他们设计了一种新的跳跃冲击传感器，用于加固的热风速计，专门设计用于在跳跃层内部署。表征质量通量分布将具有理论和应用意义。以物理为基础的剖面特征可以提高风成输送模式的预测能力。此外，众所周知，与风洞研究中输运关系推导相关的缩放约束要求原型缩放模型应基于原型数据。这项研究将提供这样一个基础。因此，这些结果将有可能解决关于通量剖面分布的长期争论，改进运输模式，并最终提高规划和应对风沙对环境影响的能力，包括沙丘形成或风蚀。这有利于地貌学家、地理学家、地质学家、工程师、物理学家和数学家，以及关注风沙各个方面的规划者。该项目还将发展国际研究合作。

Windblown particles reshape many of the Earth's landscapes; these are known as aeolian processes and certain fundamental aspects are still unknown. In fact, predicting aeolian transport rates is a keystone in the geomorphological quest to develop deterministic models for the modification of erodible surfaces by wind (erosion, accretion, and development of bed forms) and for the creation and evolution of coastal and arid dune systems. Understanding of the dynamics of wind-blown sand systems has improved dramatically over the last three decades. There remains, however, considerable dissatisfaction with the prediction of sand transport rates using basic environmental information, such as wind speed and mean sand grain size, and in relation to particular aeolian systems. In particular, there does not exist agreement as to the characteristic distribution of saltating grains above a sand surface for even the most basic transport systems. This is important because the distribution of moving grains is a fundamental control on the total rate of sand transport. This project is designed to elucidate the singular characteristics of the vertical distribution of wind-driven, saltating sand grains in a natural environment. In particular, the investigators will assess the applicability of the Rouse concentration profile model to aeolian saltation by collecting and analyzing a high-quality field data set. The Rouse concentration profile normalizes vertical particle distributions according to discernable characteristics of grain size and wind shear velocity, and its utility has been demonstrated for hydrodynamic systems. The investigators hypothesize that the vertical distribution of aeolian saltation corresponds with the Rouse profile model; that the Rouse parameter corrects some of the variability between mass-flux profiles obtained under different environmental conditions; and that the characteristics of mass-flux profiles measured in the field will be statistically distinct from those measured in wind tunnel experiments. They approach this issue through the design of an innovative, spatially and temporally detailed experiment that will measure the vertical structures of the near-surface wind and saltation fields. They have designed a new saltation impact-sensor to be used with ruggedized thermal anemometers, specially designed for deployment within the saltation layer. Characterizing the mass-flux profile will have theoretical and applied implications. A physically-based characterization of the profile should improve the predictive capacities of aeolian transport models. Further, well-known scaling constraints associated with the derivation of transport relationships from wind tunnel studies mandate that prototype-scaled models should be based on prototype data. This study will provide one such basis. As a result, the results will have the potential to resolve a longstanding debate about the flux-profile distribution, to improve transport models, and, ultimately to enhance the ability to plan for and against the environmental impacts of blowing sand, including dune building or aeolian abrasion. This benefits the communities of geomorphologists, geographers, geologists, engineers, physicists and mathematicians, and planners concerned with the various aspects of blowing sand. The project will also develop international research collaborations.