A scale-dependent model to represent changing aerodynamic roughness of ablating glacier ice based on repeat topographic surveys. Issue 260 (4th December 2020)

• Record Type: Journal Article
• Authors: Smith, Thomas; Smith, Mark W.; Chambers, Joshua R.; Sailer, Rudolf; Nicholson, Lindsey; Mertes, Jordan; Quincey, Duncan J.; Carrivick, Jonathan L.; Stiperski, Ivana
• Is Part Of: Journal of Glaciology. Volume 66:Issue 260(2020)
• Page Start: 950
• Page End: 964
• Publication Date: 2020-12-04
• Subjects: Energy balance modelling, -- glacier melt, -- ice roughness, -- structure from motion photogrammetry
• DOI: 10.1017/jog.2020.56
• Languages: English
• ISSNs: 0022-1430

Abstract

Abstract: Turbulent fluxes make a substantial and growing contribution to the energy balance of ice surfaces globally, but are poorly constrained owing to challenges in estimating the aerodynamic roughness length ( z 0 ). Here, we used structure from motion (SfM) photogrammetry and terrestrial laser scanning (TLS) surveys to make plot-scale 2-D and 3-D microtopographic estimations of z 0 and upscale these to map z 0 across an ablating mountain glacier. At plot scales, we found spatial variability in z 0 estimates of over two orders of magnitude with unpredictable z 0 trajectories, even when classified into ice surface types. TLS-derived surface roughness exhibited strong relationships with plot-scale SfM z 0 estimates. At the glacier scale, a consistent increase in z 0 of ~0.1 mm d −1 was observed. Space-for-time substitution based on time since surface ice was exposed by snow melt confirmed this gradual increase in z 0 over 60 d. These measurements permit us to propose a scale-dependent temporal z 0 evolution model where unpredictable variability at the plot scale gives way to more predictable changes of z 0 at the glacier scale. This model provides a critical step towards deriving spatially and temporally distributed representations of z 0 that are currently lacking in the parameterisation of distributed glacier surface energy balance models.