Multiscale Coupling of Boundary Layer Flow Turbulence and Sand Streamer Dynamics

Wind-driven sand transport at the Earth's surface exhibits pronounced spatiotemporal variability, forming elongated sand streamers that critically control sand flux. Despite their importance, the detailed fundamental mechanisms governing streamer formation remain elusive. This study presents results from a novel image-processing algorithm analyzing high-resolution video imagery combined with 3D wind measurement in turbulent boundary layer flow over a sandy beach. Streamers are shown to align with high-momentum pathways modulated by large-scale turbulence structures, and sand flux inside streamers scales with flow forcing. Streamer width remains invariant and decoupled from flow forcing, whereas streamer spacing increases with wind speed. These results support a top-down modulation mechanism where the invariant streamer width is likely governed by the height of the turbulent footprint, whereas the increased spacing may relate to spanwise dilation of vortex scales or a near-surface momentum feedback mediated by the saltating sand.