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United States Department of Agriculture

Agricultural Research Service

Title: Vertical Profiles of Horizontal Mass Fluxes of Wind Eroded Particles (D > 50 Micrometers) Related to Friction Velocity and Distance Downwind at Owens (Dry) Lake, California.

item Gillette, Dale - NOAA
item Fryrear, Donald
item Stockton, Paul - SENSIT CO.
item Gill, Thomas
item Ley, Trevor - CO. INST. RES. ENVI. SCI

Submitted to: Journal of Geophysical Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 6, 1997
Publication Date: N/A

Interpretive Summary: This study of the flux of particles greater than 50 micrometers showed that (1) for coarse-textured soils, one measurement may be used to estimate the integrated flux of airborne particles from ground level to one meter. For fine textured soils, at least three measurements must be used, however. (2) The flux of particles greater than 50 micrometers may be divided into saltation flux and suspension flux; as the distance of eroding sediment increases, the ratio of the suspension flux to saltation flux increases (up to the limit of this experiment - 1.5 km).

Technical Abstract: We performed a field experiment at Owens (Dry) Lake, CA, to test whether and in what manner the relative profiles of airborne horizontal mass fluxes for wind eroded particles larger than 50 micrometers changed with friction velocity. Results showed that the horizontal mass flux at almost all measured heights increased proportional to the cube of friction velocity (u*) above an apparent threshold friction velocity increased with height except at a site having a coarse "sand" sediment; only that site had a relative horizontal mass flux profile that did not change with friction velocity. Size distributions for long-time-averaged horizontal mass flux samples showed that a saltation layer may extend from the surface to a height more than 50 cm. Above this layer, suspended particles dominate. Measurements taken in a large source area on a line parallel to the wind showed that even though the saltation flux had come to equilibrium at about 650 m downwind of the starting point of erosion, weakly-suspended particles were still being input into the atmosphere at 1667 m downwind of the starting point. Therefore, the saltating fraction of the total mass flux decreased after 650 m. This scale length difference and the ratio of 70/30 suspended mass flux to saltation mass flux at the farthest downwind sampling site confirm that the suspended particles are very important for mass budgets in large source areas of dust and that saltation mass flux can be a variable fraction of the total horizontal mass flux for soils having a substantial fraction of particles smaller than 100 micrometers.

Last Modified: 4/21/2015
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