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Title: Large-eddy simulations of surface roughness parameter sensitivity to canopy-structure characteristics

Abstract

Surface roughness parameters, namely the roughness length and displacement height, are an integral input used to model surface fluxes. However, most models assume these parameters to be a fixed property of plant functional type and disregard the governing structural heterogeneity and dynamics. In this study, we use large-eddy simulations to explore, in silico, the effects of canopy-structure characteristics on surface roughness parameters. We performed a virtual experiment to test the sensitivity of resolved surface roughness to four axes of canopy structure: (1) leaf area index, (2) the vertical profile of leaf density, (3) canopy height, and (4) canopy gap fraction. We found roughness parameters to be highly variable, but uncovered positive relationships between displacement height and maximum canopy height, aerodynamic canopy height and maximum canopy height and leaf area index, and eddy-penetration depth and gap fraction. We also found negative relationships between aerodynamic canopy height and gap fraction, as well as between eddy-penetration depth and maximum canopy height and leaf area index. We generalized our model results into a virtual "biometric" parameterization that relates roughness length and displacement height to canopy height, leaf area index, and gap fraction. Using a decade of wind and canopy-structure observations in a site inmore » Michigan, we tested the effectiveness of our model-driven biometric parameterization approach in predicting the friction velocity over heterogeneous and disturbed canopies. We compared the accuracy of these predictions with the friction-velocity predictions obtained from the common simple approximation related to canopy height, the values calculated with large-eddy simulations of the explicit canopy structure as measured by airborne and ground-based lidar, two other parameterization approaches that utilize varying canopy-structure inputs, and the annual and decadal means of the surface roughness parameters at the site from meteorological observations. We found that the classical representation of constant roughness parameters (in space and time) as a fraction of canopy height performed relatively well. Nonetheless, of the approaches we tested, most of the empirical approaches that incorporate seasonal and interannual variation of roughness length and displacement height as a function of the dynamics of canopy structure produced more precise and less biased estimates for friction velocity than models with temporally invariable parameters.« less

Authors:
 [1];  [1];  [1];  [2]
  1. The Ohio State Univ., Columbus, OH (United States). Dept. of Civil, Environmental and Geodetic Engineering
  2. Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Civil and Environmental Engineering
Publication Date:
Research Org.:
The Ohio State Univ., Columbus, OH (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States); Univ. of Michigan, Ann Arbor, MI (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER); National Science Foundation (NSF); National Aeronautics and Space Administration (NASA)
OSTI Identifier:
1197768
Alternate Identifier(s):
OSTI ID: 1457230
Grant/Contract Number:  
SC0006708; SC0007041; FC02-06ER64158; 7096915; DEB-0911461; DGE-0504552; NNX11AL45H; PAS0409-4
Resource Type:
Journal Article: Published Article
Journal Name:
Biogeosciences (Online)
Additional Journal Information:
Journal Name: Biogeosciences (Online) Journal Volume: 12 Journal Issue: 8; Journal ID: ISSN 1726-4189
Publisher:
Copernicus Publications, EGU
Country of Publication:
Germany
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES

Citation Formats

Maurer, K. D., Bohrer, G., Kenny, W. T., and Ivanov, V. Y. Large-eddy simulations of surface roughness parameter sensitivity to canopy-structure characteristics. Germany: N. p., 2015. Web. doi:10.5194/bg-12-2533-2015.
Maurer, K. D., Bohrer, G., Kenny, W. T., & Ivanov, V. Y. Large-eddy simulations of surface roughness parameter sensitivity to canopy-structure characteristics. Germany. https://doi.org/10.5194/bg-12-2533-2015
Maurer, K. D., Bohrer, G., Kenny, W. T., and Ivanov, V. Y. 2015. "Large-eddy simulations of surface roughness parameter sensitivity to canopy-structure characteristics". Germany. https://doi.org/10.5194/bg-12-2533-2015.
@article{osti_1197768,
title = {Large-eddy simulations of surface roughness parameter sensitivity to canopy-structure characteristics},
author = {Maurer, K. D. and Bohrer, G. and Kenny, W. T. and Ivanov, V. Y.},
abstractNote = {Surface roughness parameters, namely the roughness length and displacement height, are an integral input used to model surface fluxes. However, most models assume these parameters to be a fixed property of plant functional type and disregard the governing structural heterogeneity and dynamics. In this study, we use large-eddy simulations to explore, in silico, the effects of canopy-structure characteristics on surface roughness parameters. We performed a virtual experiment to test the sensitivity of resolved surface roughness to four axes of canopy structure: (1) leaf area index, (2) the vertical profile of leaf density, (3) canopy height, and (4) canopy gap fraction. We found roughness parameters to be highly variable, but uncovered positive relationships between displacement height and maximum canopy height, aerodynamic canopy height and maximum canopy height and leaf area index, and eddy-penetration depth and gap fraction. We also found negative relationships between aerodynamic canopy height and gap fraction, as well as between eddy-penetration depth and maximum canopy height and leaf area index. We generalized our model results into a virtual "biometric" parameterization that relates roughness length and displacement height to canopy height, leaf area index, and gap fraction. Using a decade of wind and canopy-structure observations in a site in Michigan, we tested the effectiveness of our model-driven biometric parameterization approach in predicting the friction velocity over heterogeneous and disturbed canopies. We compared the accuracy of these predictions with the friction-velocity predictions obtained from the common simple approximation related to canopy height, the values calculated with large-eddy simulations of the explicit canopy structure as measured by airborne and ground-based lidar, two other parameterization approaches that utilize varying canopy-structure inputs, and the annual and decadal means of the surface roughness parameters at the site from meteorological observations. We found that the classical representation of constant roughness parameters (in space and time) as a fraction of canopy height performed relatively well. Nonetheless, of the approaches we tested, most of the empirical approaches that incorporate seasonal and interannual variation of roughness length and displacement height as a function of the dynamics of canopy structure produced more precise and less biased estimates for friction velocity than models with temporally invariable parameters.},
doi = {10.5194/bg-12-2533-2015},
url = {https://www.osti.gov/biblio/1197768}, journal = {Biogeosciences (Online)},
issn = {1726-4189},
number = 8,
volume = 12,
place = {Germany},
year = {Thu Apr 30 00:00:00 EDT 2015},
month = {Thu Apr 30 00:00:00 EDT 2015}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at https://doi.org/10.5194/bg-12-2533-2015

Citation Metrics:
Cited by: 29 works
Citation information provided by
Web of Science

Figures / Tables:

Table 1 Table 1: Description of simulation cases used for sensitivity analysis of roughness parameters derived from an LES over variable canopy layouts, and the resulting roughness parameters for each simulation case. Canopy structure was varied along four axes – (a) LAI, (b) vertical LAD profile, (c) canopy height, and (d) gapmore » fraction – and included an additional (e) realistic simulation case.« less

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