Title: Aerodynamic and Scalar Roughness over Snow and Sea Ice

Abstract:

In Monin-Obukhov similarity theory, the aerodynamic roughness, z0, is the artificial 
height above the surface at which the wind speed profile in the atmospheric surface layer 
extrapolates downward to zero wind speed (assuming no-slip boundary conditions).  
Likewise, the scalar roughnesses for the surface-layer profiles of temperature (zT) and 
specific humidity (zQ) are the artificial heights at which these profiles extrapolate 
downward to the surface temperature and surface humidity.  Besides their role in 
establishing the surface-layer wind speed, temperature, and humidity profiles, roughness 
lengths are often the cornerstone of so-called bulk turbulent flux algorithms, which are 
used in models, among other applications, to couple the surface and the atmosphere through 
the surface fluxes of momentum and sensible and latent heat. In this talk, I will review 
the theory and measurement of the aerodynamic and scalar roughness lengths over snow and 
sea ice.  The data consist of thousands of hours of eddy-covariance flux measurements over 
both Arctic and Antarctic sea ice.  In winter, sea ice is horizontal and snow-covered and, 
therefore, is similar to extensive snow-covered surfaces on land.  As a result, what we 
learn about the roughness of winter sea ice should apply to any extensive snow fields. 
Although z0, zT, and zQ are not true physical quantities, I will describe recent efforts 
that link z0 to the physical roughness of sea ice, a quantity that can conceivably be 
measured from satellites.  I will also highlight some of the misconceptions that exist 
about parameterizing roughness lengths.