Derivation of Turbulent Flux Profiles and Roughness Lengths from Katabatic Flow Dynamics

Abstract

The dynamics of katabatic flows have been used to determine the vertical momentum flux profiles and surface roughness lengths under stable conditions on glacier surfaces. By assuming a momentum budget balance between katabatic forcing and vertical flux divergence of horizontal momentum in the region beneath the wind maximum, it is possible to derive the vertical momentum flux profile by integrating the temperature deficit. Using the surface flux determined in this way and appropriate profile fits, the roughness length for momentum can be derived. The roughness length obtained in this way agrees well with estimates made under nonkatabatic conditions using standard log-linear fits. The katabatically determined fluxes were compared with eddy correlation measurements and with bulk methods. The eddy correlation measurements were not always in agreement with the katabatic fluxes; the comparison with bulk-derived fluxes, however, was particularly good.