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Geosci. Model Dev., 11, 1467-1496, 2018
https://doi.org/10.5194/gmd-11-1467-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Development and technical paper
16 Apr 2018
Modeling canopy-induced turbulence in the Earth system: a unified parameterization of turbulent exchange within plant canopies and the roughness sublayer (CLM-ml v0)
Gordon B. Bonan1, Edward G. Patton1, Ian N. Harman2, Keith W. Oleson1, John J. Finnigan2, Yaqiong Lu1, and Elizabeth A. Burakowski3 1National Center for Atmospheric Research, P.O. Box 3000, Boulder, Colorado, USA 80307
2CSIRO Oceans and Atmosphere, Canberra, Australia
3Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire, USA
Abstract. Land surface models used in climate models neglect the roughness sublayer and parameterize within-canopy turbulence in an ad hoc manner. We implemented a roughness sublayer turbulence parameterization in a multilayer canopy model (CLM-ml v0) to test if this theory provides a tractable parameterization extending from the ground through the canopy and the roughness sublayer. We compared the canopy model with the Community Land Model (CLM4.5) at seven forest, two grassland, and three cropland AmeriFlux sites over a range of canopy heights, leaf area indexes, and climates. CLM4.5 has pronounced biases during summer months at forest sites in midday latent heat flux, sensible heat flux, gross primary production, nighttime friction velocity, and the radiative temperature diurnal range. The new canopy model reduces these biases by introducing new physics. Advances in modeling stomatal conductance and canopy physiology beyond what is in CLM4.5 substantially improve model performance at the forest sites. The signature of the roughness sublayer is most evident in nighttime friction velocity and the diurnal cycle of radiative temperature, but is also seen in sensible heat flux. Within-canopy temperature profiles are markedly different compared with profiles obtained using Monin–Obukhov similarity theory, and the roughness sublayer produces cooler daytime and warmer nighttime temperatures. The herbaceous sites also show model improvements, but the improvements are related less systematically to the roughness sublayer parameterization in these canopies. The multilayer canopy with the roughness sublayer turbulence improves simulations compared with CLM4.5 while also advancing the theoretical basis for surface flux parameterizations.
Citation: Bonan, G. B., Patton, E. G., Harman, I. N., Oleson, K. W., Finnigan, J. J., Lu, Y., and Burakowski, E. A.: Modeling canopy-induced turbulence in the Earth system: a unified parameterization of turbulent exchange within plant canopies and the roughness sublayer (CLM-ml v0), Geosci. Model Dev., 11, 1467-1496, https://doi.org/10.5194/gmd-11-1467-2018, 2018.
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Short summary
Land surface models neglect the roughness sublayer and parameterize within-canopy turbulence in an ad hoc manner. We implemented a roughness sublayer parameterization in a multilayer canopy model to test if this theory provides a tractable parameterization extending from the ground through the canopy and the roughness sublayer. The multilayer canopy improves simulations compared with the Community Land Model (CLM4.5) while also advancing the theoretical basis for surface flux parameterizations.
Land surface models neglect the roughness sublayer and parameterize within-canopy turbulence in...
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