Large-scale variability of wind erosion mass flux rates at Owens Lake 2. Role of roughness change, particle limitation, change of threshold friction velocity, and the Owen effect

Abstract

Variability in airborne particles larger than sand flux for distance scales larger than 200 m was observed during wind erosion episodes on the northeast side of a dry lake bed (Owens Lake). Measurements were made during erosion episodes on a ∼3-km line of wind measuring and sand flux collecting instruments. Data were selected for winds that (1) aligned with the instrument line and (2) had mean speeds cubed at 4-m heights at the beginning, middle, and end of the line that differed by less than 5% (i.e., mean wind speeds differed by less than 1.7%). Four mechanisms were determined to cause the large-scale differences in the mass flux profiles. In order of their importance, the mechanisms are as follows: (1) change of the drag coefficient (or the ratio u*/U, where u* is wind friction velocity and U is mean wind speed from place to place), this is a measure of variability in roughness height; (2) particle limitation (depletion of the loose "available" erodible material on the surface); (3) variation of the threshold friction velocity; and (4) the Owen effect (the increase of u*/U with U).