University of Colorado at Boulder

Colloquia Event

Friday April 30, 2010. 03:30 pm. Gugg 205

Small Scale Snowpack Surface Roughness Variability Measurements

Steven Fassnacht

Watershed Science Program, Colorado State University

The surface of the snow is the interface between the snowpack and the atmosphere. The movement of air across this interface yields mass and heat fluxes to and from the surface resulting in sublimation and redistribution of snow. There is a feedback between the movement of air and the snow surface roughness, which can change the surface characteristics and the fluxes. Digital photographs of a black board inserted into the snow surface were used to assess the physical surface roughness; it was measured with the random roughness and variogram analysis. The former is a roughness index that does not consider the spatial structure while the latter yields the fractal dimension for specific measurement scales. The photographic method was evaluated versus manual measurements.

The snowpack surface roughness varies temporally and spatially, especially considering the direction of roughness due to wind effects. There is consistency in roughness over different scales, yet large scale processes (e.g., wind and radiation activity) influence the magnitude of roughness much more than small scale processes (e.g., crystal form and metamorphism). There is no significant change in surface roughness during the accumulation season. However, during the melting season roughness increases, but can be reduced by the deposition of aeolian constituents. The impacts of aeolian deposits on snow surface albedo and roughness as well as the implications of temporally varying surface roughness on snowpack sublimation losses are currently being investigated