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.
