Dry-Air Entrainment and Advection during Alpine Blowing Snow Events

Abstract

Abstract. Blowing snow transport has considerable impact on the hydrological cycle in alpine regions both through the redistribution of the seasonal snowpack and through sublimation back into the atmosphere. Alpine energy and mass balances are typically modelled with time-averaged approximations of sensible and latent heat fluxes. This oversimplifies non-stationary turbulent mixing in complex terrain and may overlook important exchange processes for hydrometeorological prediction. To determine if warm and dry air advection during blowing snow events from atmospheric sweep and ejection motions can provide such exchange mechanisms, they were investigated at an alpine site in the Canadian Rockies and found to supply substantial sensible heat to blowing snow flows. These motions were responsible for temperature fluctuations of up to 1 °C, a considerable change for energy balance estimation. A simple scaling relation was derived that related the frequency of turbulent sweeps and ejections to the event magnitude. This allows the first parameterization of entrained or advected energy for time-averaged representations of blowing snow sublimation and suggests that advection can strongly reduce thermodynamic feedbacks between blowing snow sublimation and the near-surface atmosphere. The recurrence model modeled described provides a significant step towards a more physically-based blowing snow sublimation model. Additionally, calculations of return frequencies and event durations provide a field-measurement context for recent findings of non-stationarity impacts on sublimation rates.