Vertical distribution of grain size for wind blown sand

Grain size-sorting characteristics from twenty-five vertical, mass-flux profiles for a mixed grain population are presented from a field study conducted in Jericoacoara, Brazil. The vertical mass flux profile is best described using an exponential decay function. An analysis of the grain-size statistics shows that a reverse in grain-size trends occurs at an inflection zone located 0.05-0.15. m above the bed. Below this inflection, mean grain-size decreases steeply with elevation in the near bed region dominated by reptation and saltation modes of transport. Above the inflection there is a coarsening of grain size with elevation. Sorting improves with elevation above the surface. There is not a strong relationship between skewness and kurtosis with elevation. The grain-size inflection above the surface is a characteristic of saltation in some natural environments, with important implications for numerical modeling of grain trajectories.