Collaborative Research: Small-Scale Variability in Aeolian Sand Transport

该项目将审查自然环境中沙子和其他松散材料在风力驱动下移动的小尺度变异性的特征和驱动因素，并特别注意与跳跃拖缆的组织和动态有关的沙子输送的水平变异性。该项目基于两个概念：(1)如果风吹过含有松散或松散的沙粒的表面的速度足够快，一些沙粒将被气流卷走并顺风输送，(2)风吹得越快，产生的传输率就越大。这两个基本概念是用于理解和预测风沙运移速率和特定风沙地貌演变的机械数学模型的指导性假设。在地球和火星的干旱地区，风是主要的地表过程；风产生的或风修改的地貌覆盖了地球和火星的大部分陆地表面。吹沙主要是通过跃迁过程，通过泄气(盘)、吸积(沙丘)和磨损(雅丹)造成了许多这样的地貌。在许多陆地环境中，吹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，了解跳跃的特征和控制是了解和管理这种环境的基础。本项目的重点是自然环境中风沙跃迁的小尺度变率的特征和驱动因素，并特别注意跃迁飘带的组织和平流。研究人员将在巴西杰里科阿卡拉进行一套全面的现场实验，以收集风沙的点和面测量以及风系统的详细测量，以便表征拖带的物理尺寸、速度、拖带内外的跃升强度，以及风和扬沙中的不稳定和空间不均匀之间的关系。巴西东北海岸的位置非常适合进行研究，因为在那里刮起的信风很稳定。研究人员还将研究“上层建筑”，即在湍流边界层内发现的米到公里大小的运动，以确定上层建筑是否导致了流光的形成。这个项目将量化几小时和几米尺度上的传输可变性，并应指导未来的实验设计，在将进行点状测量传输的情况下。研究结果应为未来研究的评价和对过去研究的重新评价提供必要的信息。该项目应促进对风和跃迁相互作用的基本了解，特别是在将风中连贯的湍流结构(上层建筑)与跃迁结构类似物(拖缆)联系起来的情况下。由于运输可变性通常被描述为改善运输率预测的障碍，更好地再现原型条件的模型将通过向环境管理人员和规划者提供高质量的预测，提高规划和缓解吹沙对环境影响的能力。项目成果将为将目前的风沙制度外推到未来可供选择的气候和假设的外星环境中的风沙制度提供更好的基础。

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.