On the relative importance of saltation and suspension for aeolian snow mass transport

Abstract

AbstractSnow transport affects various hydrological processes significantly through reshaping the glacial landscapes. Snow particles that are transported in a turbulent flow are typically classified under the saltation and suspension states based on the inertia of the particles relative to the strength of the turbulence. In this study, snow transport in the turbulent boundary layer was simulated using the large‐eddy simulation with Lagrangian particle tracking method. Contrary to most previous studies in which saltation and suspension are defined by a specified critical height or particle size, hop time ratio Rt and particle Stokes number St were adopted to judge the state of saltating snow particles, and the contributions of pure saltation, modified saltation, short‐ and long‐term suspension particles were quantified appropriately. A threshold value of St≈5 for pure saltation was proposed through the particle trajectory comparison. The results show that the St criterion measures pure saltation particle appropriately but fails to diagnose long‐term suspension particles. Furthermore, although there are hardly any pure saltation particles in natural snow transport, the contribution of modified saltation cannot be neglected in the lowest centimetres of the atmosphere, which may also dominate the overall mass flux at the near surface under larger friction velocities. Rather, considerable short‐ and long‐term suspended particles spread over the entire vertical dimension of the snow cloud, contributing a major proportion of the overall mass flux, even within the saltation layer. Based on this, the suspension layer should be defined as the entire vertical dimension of the particle cloud. The results can improve our understanding of the motion dynamics of transported snow particles and further provide new ideas in modelling this process.