Abstract
Spatially-distributed values of glacier aerodynamic roughness (z0) are vital for robust estimates of turbulent energy fluxes and ice and snow melt. Microtopographic data allow rapid estimates of z0 over discrete plot-scale areas, but are sensitive to data scale and resolution. Here, we use an extensive multi-scale dataset from Hintereisferner, Austria, to develop a correction factor to derive z0 values from coarse resolution (up to 30 m) topographic data that are more commonly available over larger areas. Resulting z0 estimates are within an order of magnitude of previously validated, plot-scale estimates and aerodynamic values. The method is developed and tested using plot-scale microtopography data generated by structure from motion photogrammetry combined with glacier-scale data acquired by a permanent in-situ terrestrial laser scanner. Finally, we demonstrate the application of the method to a regional-scale digital elevation model acquired by airborne laser scanning. Our workflow opens up the possibility of including spatio-temporal variations of z0 within glacier surface energy balance models without the need for extensive additional field data collection.
Highlights
The aerodynamic roughness length parameter (z0) is recognized as one of the key uncertainties in glacier surface energy balance (SEB) modeling (Cullen et al, 2007; Sicart et al, 2014; Litt et al, 2017; Fitzpatrick et al, 2019)
Larger z0DEM estimates were given at each resolution when larger neighborhood sizes were used, which increased the scale over which z0DEM was calculated
We carried out a multi-scale investigation of topographic z0 over Hintereisferner, Austria
Summary
The aerodynamic roughness length parameter (z0) is recognized as one of the key uncertainties in glacier surface energy balance (SEB) modeling (Cullen et al, 2007; Sicart et al, 2014; Litt et al, 2017; Fitzpatrick et al, 2019). Quantifying z0 is essential for calculating and predicting glacier ablation because z0 is incorporated into calculations of the turbulent fluxes of sensible and latent heat between a surface and the adjacent atmosphere using the “bulk aerodynamic approach” (Hock, 2005). Using this approach, the sensible (H) and latent (LE) heat fluxes are defined as: Systematic Underestimation of Glacier Roughness. The bulk transfer coefficients CH and CE are derived from the logarithmic wind speed profile equation (assuming neutral stratification) u(z) z κ0up ln z0 (3). Substituting into Eq 1, the bulk equation for the sensible heat flux becomes
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