A scale-dependent model to represent changing aerodynamic roughness of ablating glacier ice based on repeat topographic surveys
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...
Published in: | Journal of Glaciology |
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Main Authors: | , , , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
Cambridge University Press (CUP)
2020
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Subjects: | |
Online Access: | http://dx.doi.org/10.1017/jog.2020.56 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143020000568 |
Summary: | 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. |
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