Collaborative Research: Small-Scale Variability in Aeolian Sand Transport

合作研究：风积沙输送的小尺度变化

• 批准号: 1061335
• 负责人: Douglas Sherman
• 金额: $ 9.93万
• 依托单位: Texas A&M Research Foundation
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-06-01 至 2013-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1061335&HistoricalAwards=false
• 关键词: Collaborative; Research; Small; Scale; Variability

This project will examine the characteristics and drivers of small-scale variability of wind-driven movement of sand and other unconsolidated materials in natural environments, with special attention given to the horizontal variability in sand transport associated with the organization and dynamics of saltation streamers. This project builds on two concepts: (1) if the wind blows fast enough across a surface comprising unconsolidated or poorly consolidated sand grains, some grains will be entrained by the flow and transported downwind, and (2) the faster the wind blows, the greater the resulting transport rate will be. These two basic concepts are the guiding assumptions that underpin the mechanistic, mathematical models used to comprehend and predict the rates of aeolian (wind) sand transport and evolution of particular aeolian landforms. In the arid regions of Earth and on Mars, wind is the dominant surficial process; wind-generated or wind-modified landforms cover much of the land surface of Earth and Mars. Blowing sand, moving mainly through the process of saltation, is responsible for many of those landforms via deflation (pans), accretion (dunes), and abrasion (yardangs). In many terrestrial environments, blowing sand is a critical natural hazard, but in others, it is a resource to be managed. Understanding the characteristics and controls on saltation therefore is fundamental to understanding and managing such environments. This project focuses on the characteristics and drivers of small-scale variability of aeolian saltation in natural environments, with special attention given to the organization and advection of saltation streamers. The investigators will conduct a comprehensive set of field experiments in Jericoacoara, Brazil, in order to gather point and areal measurements of wind-blown sand as well as detailed measurements of the wind system in order to characterize the physical dimensions of streamers, their velocity, the intensities of saltation within and without the streamers, and the relationship between unsteadiness and spatial non-uniformity in the wind and the blowing sand. The location on the northeast coast of Brazil is ideal for type of research because of the consistency of the tradewinds that blow onshore there. The investigators will also examine 'superstructures,' which are meter- to kilometer-sized motions found within the turbulent boundary layer, in order to determine whether superstructures cause the formation of streamers.This project will quantify the transport variability over scales of hours and meters and should guide future experimental design in instances where point measures of transport will be made. The results should provide necessary information for appraisal of future studies and the reevaluation of past studies. This project should advance basic understanding of the interactions of wind and saltation, especially in the context of linking coherent turbulent structures (superstructures) in the wind with the saltation structure analog (streamers). Because transport variability is commonly described as a hurdle to improving transport rate predictions, models that better reproduce prototype conditions will enhance the ability to plan for and to alleviate the environmental impacts of blowing sand by providing high-quality predictions to environmental managers and planners. Project results will provide a better foundation for the extrapolation of current aeolian regimes to those anticipated under alternative future climates and to those posited for extraterrestrial environments.

本项目将研究自然环境中沙和其他松散物质的风力驱动运动的小规模变化的特点和驱动因素，特别注意与跳跃拖缆的组织和动力学有关的沙输运的水平变化。 该项目建立在两个概念上：（1）如果风吹得足够快，穿过一个由未固结或固结不良的沙粒组成的表面，一些沙粒将被气流夹带并顺风运输，以及（2）风吹得越快，所产生的运输速率就越大。 这两个基本概念是指导性的假设，支持机械，数学模型，用于理解和预测特定的风成地貌的风成（风）沙运输和演变的速度。 在地球和火星的干旱地区，风是主要的地表变化过程;风产生或风改变的地貌覆盖了地球和火星的大部分陆地表面。 风沙主要通过跃移过程移动，通过通缩（盘），加积（沙丘）和磨损（雅丹）造成了许多地貌。 在许多陆地环境中，风沙是一种严重的自然灾害，但在其他环境中，它是一种需要管理的资源。 因此，了解突变的特点和控制是理解和管理这种环境的基础。 该项目侧重于自然环境中风成跃移的小尺度变化的特征和驱动因素，特别关注跃移流的组织和平流。 调查人员将在巴西的Jericoacoara进行一套全面的实地实验，以收集风吹沙的点和区域测量值以及风系统的详细测量值，以确定拖缆的物理尺寸、速度、拖缆内外的跳跃强度，以及风和扬沙作用下的不稳定性与空间非均匀性的关系。 巴西东北海岸的位置是理想的研究类型，因为那里吹向岸上的信风的一致性。 研究人员还将检查“上层结构”，这是在湍流边界层内发现的米到更大尺寸的运动，以确定上层结构是否会导致飘带的形成。该项目将量化小时和米尺度上的传输变化，并应指导未来的实验设计，在这种情况下，将进行点测量传输。 研究结果可为今后的研究评价和对以往研究的再评价提供必要的信息。 该项目应促进对风和跃移相互作用的基本理解，特别是在将风中的相干湍流结构（上层结构）与跃移结构模拟（飘带）联系起来的背景下。 由于迁移变异性通常被描述为改进迁移率预测的一个障碍，更好地再现原型条件的模型将通过向环境管理者和规划者提供高质量的预测来提高规划和减轻风沙环境影响的能力。 项目结果将为将目前的风成机制外推到未来其他气候条件下的预期机制和地球外环境的假设机制提供更好的基础。