Variability of the apparent von Kármán parameter during aeolian saltation

The variability of the apparent von Krmn parameter κ_a during aeolian saltation was evaluated in a field experiment at Jericoacoara, Brazil. To test this variability, velocity profiles, Reynolds stress and sand transport data were gathered and analyzed. We used 15 data sets with sand-laden airflow and 2 runs with clear airflow. Results indicated an inverse linear relationship between κ_a and bulk, gravimetric sand concentration (R² = 0.746) and sand transport rate (R² = 0.577). We found values of κ_a as low as 0.26. This means that using the von Krmn constant, κ (0.40) rather than the variable κ_a to estimate shear velocity based on the slope of the velocity profile will lead to over estimation of shear velocity, averaging about 20% in this study. This, in turn, produces an over estimation of wind-blown sand transport rates based on models that have terms with shear velocity cubed.