资源环境科技发展态势分析平台

The aerodynamic roughness length (z(0)) is an essential parameter in surface energy balance studies, but few literature values exist for debris-covered glaciers. We use microtopographic and aerodynamic methods to assess the spatial variability of z(0) for Lirung Glacier, Nepal. We apply structure from motion to produce digital elevation models for three nested domains: five 1 m(2) plots, a 21,300 m(2) surface depression, and the lower 550,000 m(2) of the debris-mantled tongue. Wind and temperature sensor towers were installed in the vicinity of the plots within the surface depression in October 2014. We calculate z(0) according to a variety of transect-based microtopographic parameterizations for each plot, then develop a grid version of the algorithms by aggregating data from all transects. This grid approach is applied to the surface depression digital elevation model to characterize z(0) spatial variability. The algorithms reproduce the same variability among transects and plots, but z(0) estimates vary by an order of magnitude between algorithms. Across the study depression, results from different algorithms are strongly correlated. Using Monin-Obukov similarity theory, we derive z(0) values from the meteorological data. Using different stability criteria, we derive median values of z(0) between 0.03 m and 0.05 m, but with considerable uncertainty due to the glacier's complex topography. Considering estimates from these algorithms, results suggest that z(0) varies across Lirung Glacier between similar to 0.005 m (gravels) to similar to 0.5 m (boulders). Future efforts should assess the importance of such variable z(0) values in a distributed energy balance model.