Abstract
Snowpack aerodynamic surface roughness length (zo) is a critical variable in estimating heat transfers to and from a snow surface and thus sublimation rates. This variable has been shown to be site specific. To illustrate a temporal variation in zo, laboratory experiments were performed using a small evaporation pan sitting on a load cell with a constant wind flow over the snow surface. Comparing multi-layer meteorological data above the pan to sublimation measured from mass change showed a decrease in the snowpack surface roughness length as the snow metamorphosed. The sensitivity of snowpack zo changes over time in modeling of sublimation was examined using hourly meteorological data for the winter of 2000-2001 at Syracuse, New York and Leadville Colorado for several scenarios, including increasing or decreasing zo after a snowfall event, considering directionality of zo as a function of the wind direction, and a ratio of latent heat to momentum roughness lengths. The base case used a constant zo of 0.01 metres. The modeled differences were a function of the values of zo, which varied with the frequency of occurrence of fresh snow and the distribution of wind from various directions. The temporal and spatial variability in surface roughness is crucial in computing the energy and mass balance of a snowpack.
Highlights
IntroductionLand surface schemes use constant snowpack zo values that are the same for sensible heat flux and latent water vapor flux computations, but may be different for momentum flux
The sublimation that was measured in the laboratory was directly from the snowpack samples
Laboratory experiments were performed that illustrated a decrease in snowpack roughness length of up to 50% over a five to seven day period
Summary
Land surface schemes use constant snowpack zo values that are the same for sensible heat flux and latent water vapor flux computations, but may be different for momentum flux. For in-depth studies of heat and vapor fluxes, the zo for a snow or sea ice surface has been defined as a function of the momentum, sensible heat, and latent water vapor fluxes (e.g., King and Anderson, 1994). These different roughness lengths, zoM, zoH, zoE, respectively, are likely influenced by the atmospheric stability (Wood and Mason, 1991). Due to scatter in their data, King and Anderson (1994) stated that the different roughness lengths were approximately equal (0.000056 m), while Andreas (1987) illustrated that they are not equal and are a function of the Reynolds, Prandtl, and Schmidt numbers, with zoH
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
