Parameterizing scalar transfer over snow and ice: A review

Evaluating the profiles of wind speed, temperature, and humidity in the atmospheric surface layer or modeling the turbulent surface fluxes of sensible and latent heat over horizontally homogeneous surfaces of snow or ice requires five pieces of information. These are the roughness lengths for wind speed (z(0)), temperature (z(T)), and humidity (z(Q)) and the stratification corrections for the wind speed and scalar profiles psi(m) and psi(h), respectively. Because over snow and ice the atmospheric surface layer is often stably stratified, the discussion here focuses first on which of the many suggested psi(m) and psi(h) functions to use over snow and ice. On the basis of four profile metrics-the critical Richardson number, the Deacon numbers for wind speed and temperature, and the turbulent Prandtl number-the manuscript recommends the Holtslag and de Bruin psi(m) and psi(h) functions because these have the best properties in very stable stratification. Next, a reanalysis of five previously published datasets confirms the validity of a parameterization for z(T)/z(0) as a function of the roughness Reynolds number (R-*) that the author reported in 1987. The z(T)/z(0) data analyzed here and that parameterization are compatible for R-* values between 10(-4) and 100, which span the range from aerodynamically smooth through aerodynamically rough flow. Discussion of a z(0) parameterization is deffered and an insufficiency of data for evaluating z(Q) is reported, although some z(Q) data is presented.