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 modeled with time-averaged approximations of sensible and latent heat fluxes. This oversimplifies nonstationary turbulent mixing in complex terrain and may overlook important exchange processes for hydrometeorological prediction. To determine if specific turbulent motions are responsible for warm- and dry-air advection during blowing snow events, quadrant analysis and variable interval time averaging was used to investigate turbulent time series from the Fortress Mountain Snow Laboratory alpine study site in the Canadian Rockies, Alberta, Canada, during the winter of 2015–2016. By analyzing wind velocity and sonic temperature time series with concurrent blowing snow, such turbulent motions were found to supply substantial sensible heat to near-surface wind flows. These motions were responsible for temperature fluctuations of up to 1 ∘C, a considerable change for energy balance estimation. A simple scaling relationship was derived that related the frequency of dominant downdraft and updraft events to their duration and local variance. This allows for 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 downdraft and updraft scaling relationship described herein provides a significant step towards a more physically based blowing snow sublimation model with more realistic mixing of atmospheric heat. Additionally, calculations of return frequencies and event durations provide a field-measurement context for recent findings of nonstationarity impacts on sublimation rates.
Highlights
At least 40 % of the world’s population relies on the seasonal snowpack as a temporary reservoir of winter snowfall that provides meltwater in spring and summer for downstream water use (Meehl et al, 2007)
Ultrasonic temperature and wind velocity time series were observed at the Fortress Mountain Snow Laboratory (FMSL) blowing snow study site using two Campbell Scientific CSAT3 sonic anemometers sampling at 50 Hz from November 2015 to March 2016
Mobbs and Dover (1993), Déry and Taylor (1996), Déry and Yau (1999, 2001), Groot Zwaaftink et al (2013), and others have suggested that blowing snow sublimation could be a self-limiting process when thermodynamic feedbacks are included in a steadystate boundary layer model
Summary
At least 40 % of the world’s population relies on the seasonal snowpack as a temporary reservoir of winter snowfall that provides meltwater in spring and summer for downstream water use (Meehl et al, 2007). Blowing snow particles are highly susceptible to sublimation because of their high curvature, large surface-area-to-mass ratio, and high ventilation rates (Dyunin, 1959; Schmidt, 1982). While estimates may vary with climate, in the Canadian Rockies, blowing snow transport has been found to be responsible for sublimating 17 %– 19 % of the yearly snowfall (MacDonald et al, 2010). Snow sublimation is typically studied at large temporal and spatial scales within hydrometeorological modeling frameworks because of the complexity of the processes and the difficulty of particle transport tracking To accurately calculate all contributions to boundary layer energy balances, latent-heat-flux estimates rely on an accurate sublimation model and a precise understanding of how much energy is available for snow particle
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