The aerodynamic roughness length of fresh snow

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Description/Abstract

This study presents the results from a series of wind-tunnel experiments designed to investigate the aerodynamic roughness length z 0 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 z 0. Our results show that, under aerodynamically rough conditions, the mean value of the roughness length for fresh snow is [z0] = 0.24z0=024 mm with a standard deviation σ(z 0) = 0.05 mm. In this study, we show that variations in z 0 are associated with variations in the roughness geometry. The roughness measurements suggest that the estimated values of z 0 are consistent with the presence of irregular roughness structures that develop during snowfalls that mimic ballistic deposition processes