Aerodynamic roughness length of fresh snow

This study presents the results from a series of wind-tunnel experiments designed to investigate the aerodynamic roughness length z0 of fresh snow under no-drift conditions. A two-component hot-film anemometer was employed to obtain vertical profiles of velocity statistics in a zero pressure gradient turbulent boundary layer for flow over naturally deposited snow surfaces. The roughness of these snow surfaces was measured by means of digital photography to capture characteristic length scales that can be related to z0. Our results show that, under aerodynamically rough conditions, the mean value of the roughness length for fresh snow is =0.24 mm with a standard deviation s(z0) = 0.05 mm. In this study, we show that variations in z0 are associated with variations in the roughness geometry. The roughness measurements suggest that the estimated values of z0 are consistent with the presence of irregular roughness structures that develop during snowfalls that mimic ballistic deposition processes