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Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/5/2014 Publication Date: 8/1/2014 Citation: Stout, J.E. 2014. Detecting patterns of aeolian transport direction. Journal of Arid Environments. 107:18-25. Interpretive Summary: In the study of wind erosion, magnitude and direction of sediment transport are both important parameters. Although the magnitude of sediment transport has been studied extensively, the study of aeolian transport direction has received less attention. This paper outlines a new experimental technique for detecting the direction that shifting winds transport sediments. Using a sampling system that can be left unattended at remote sites for extended periods, the output from a sensor capable of detecting particle impacts was used as an indicator of blowing sediment, which allowed the number of seconds with active sediment movement to be counted and assigned to a given wind direction. Continuous measurements of blowing sediment collected over a fourteen-year period at a salt playa site provided the raw data from which transport direction was computed. Results suggest that westerly winds contributed the most to the erosion and transport of sediments from the dry playa lakebed. This result is consistent with the well-established finding that wind erosion events and dust storms are most often associated with dry westerly winds that blow across the Llano Estacado from the dry desert lands of New Mexico to the west. The results also reveal the significant contribution of northerly winds associated with dry cold fronts that often pass through the area during the winter and fall seasons. Technical Abstract: The magnitude and direction of aeolian transport are of direct interest to those engaged in the study of aeolian processes. Although the magnitude of sediment transport has been studied extensively, the study of aeolian transport direction has garnered less attention. This paper describes the development of an experimental technique that provides a means of detecting aeolian transport direction. This technique involves detecting one-second periods of blowing sediment, called saltation seconds, with a piezoelectric saltation sensor and assigning active periods to one of sixteen principal wind directions. Saltation seconds are summed separately for each wind direction sector to compute the relative fraction associated with a specific wind direction. Measurements of aeolian activity collected over a fourteen-year period at a large saline playa on the Llano Estacado of North America were used to compute the relative frequency that sediments are transported by winds blowing from a specific direction. The successful completion of this field study and subsequent analysis demonstrate that useful information regarding sediment transport direction can be obtained with an unattended sampling system collecting data at a remote field location. Specific results of this study suggest that the overall majority of all saltation seconds were associated with winds with a westerly component including winds blowing out of the south-southwest, southwest, west-southwest, west, and west-northwest sectors. This result is consistent with the well-established finding that wind erosion and sand storms are most often associated with dry westerly and southwesterly winds that blow across the Llano Estacado. Results also reveal that there are subtle seasonal shifts of aeolian transport direction associated with seasonal shifts in the wind regime. During the spring, the highest fraction of saltation seconds was associated with south-southwesterly winds and during the summer there is a prominent peak corresponding to southerly winds. There is a significant contribution of northerly winds transporting sediments to the south during the fall and winter seasons when strong northerly winds, associated with dry continental polar cold fronts, often pass through the area. |
