**Geometric Versus Anemometric Surface Roughness for a Shallow Accumulating Snowpack**

**Jessica E. Sanow 1,2, Steven R. Fassnacht 2,3,4,\*, David J. Kamin 3,5, Graham A. Sexstone 6, William L. Bauerle 7 and Iuliana Oprea 8**


Received: 2 November 2018; Accepted: 1 December 2018; Published: 6 December 2018

**Abstract:** When applied to a snow-covered surface, aerodynamic roughness length, *z*0, is typically considered as a static parameter within energy balance equations. However, field observations show that *z*0 changes spatially and temporally, and thus *z*0 incorporated as a dynamic parameter may greatly improve models. To evaluate methods for characterizing snow surface roughness, we compared concurrent estimates of *z*0 based on (1) terrestrial light detection and ranging derived surface geometry of the snowpack surface (geometric, *<sup>z</sup>*0*G*) and (2) vertical wind profile measurements (anemometric, *<sup>z</sup>*0*A*). The value of *z*0*G* was computed from Lettau's equation and underestimated *z*0*A* but compared well when scaled by a factor of 2.34. The Counihan method for computing *z*0*G* was found to be unsuitable for estimating *z*0 on a snow surface. During snowpack accumulation in early winter, *z*0 varied as a function of the snow-covered area (SCA). Our results show that as the SCA increases, *z*0 decreases, indicating there is a topographic influence on this relation.

**Keywords:** aerodynamic roughness length; terrestrial lidar; snow surface topography; wind profile; snow energy balance; snow accumulation
