Characteristics of near-surface atmospheric flow and turbulent heat fluxes under highly stable conditions over a snow-covered alpine glacier

The evolution of a snow pack is mainly controlled by the surface energy balance; however, most previous studies have failed to close this budget on short time scales. This is often due to a lack of precise data required to calculate the subsurface heat flux but also associated to problems with the measurement and the interpretation of turbulent heat fluxes under extremely stable conditions. Especially the latter is an issue when vertical temperature gradients exceed 5ºC/m in the lowest 3m of the atmosphere and when the wind velocity is very small. Such conditions have been measured over a snow-covered glacier in the Swiss Alps during the winters of 2006-2008 to investigate snow-atmosphere interaction. Turbulent fluxes were measured both in horizontal and vertical arrays to identify the dominant physical processes. First results suggest that turbulence can be intermittent with occasional presence of sweeps and ejections and broken into periods when turbulence is very week and the flow almost laminar. Furthermore, the data indicate vertical gradients of the turbulent heat fluxes, in contrast to the constant flux layer assumption. That is, near-surface fluxes (z<1m) appear to be decoupled from fluxes at higher levels (z>3m) above the surface.