Abstract. We hypothesize that large eddies play a major role in the entrainment of aeolian particles. To test this, wind-tunnel experiments are carried out to measure the particle entrainment rate for various sizes and flow conditions. Wind-tunnel flows are usually neutrally stratified with no large eddies, which are typically seen in convective atmospheric boundary layers. Here, a novel technique is applied, by deploying a piece of randomly fluttering cloth, to generate large eddies similar to convective eddies, here referred to as quasi-convective turbulence. The characteristics of quasi-convective turbulence are analyzed with respect to neutral turbulence in the Monin–Obukhov similarity framework, and the probability distributions of surface shear stress are examined. We show that for a given mean flow speed and in comparison with neutral flow conditions, quasi-convective turbulence increases the surface shear stress and alters its probability distribution and hence substantially enhances the entrainment of sand and dust particles. Our hypothesis is thus confirmed by the wind-tunnel experiments. We also explain why large eddies are important to aeolian entrainment and transport.

Abstract. We hypothesize that large eddies play a major role in the entrainment of aeolian sand and dust particles. To test this, wind-tunnel experiments are carried out to measure the entrainment rate of various particle sizes under different flow conditions. Wind tunnel flows are usually neutrally stratified with no large eddies which typically develop in convective atmospheric boundary layers. Here, a novel technique is applied by deploying a piece of randomly fluttering cloth to generate large eddies similar to convective eddies in atmospheric boundary layers, which we call quasi-convective turbulence. The characteristics of quasi-convective turbulence are analyzed with respect to neutral turbulence in the Monin-Obukhov similarity framework, and the probability distributions of surface shear stress are examined. We show that for given mean flow speed and in comparison with neutral flow conditions, quasi-convective turbulence increases the surface shear stress and alters its probability distribution, and hence substantially enhances the entrainment of sand and dust particles. Our hypothesis is thus confirmed by the wind-tunnel experiments. We also explain why large eddies are important to aeolian entrainment and transport.