Articles | Volume 21, issue 6
Hydrol. Earth Syst. Sci., 21, 2987–3000, 2017
Hydrol. Earth Syst. Sci., 21, 2987–3000, 2017

Research article 20 Jun 2017

Research article | 20 Jun 2017

Explaining the convector effect in canopy turbulence by means of large-eddy simulation

Tirtha Banerjee1,a, Frederik De Roo1, and Matthias Mauder1 Tirtha Banerjee et al.
  • 1Karlsruhe Institute of Technology (KIT) Institute of Meteorology and Climate Research, Atmospheric Environmental Research (IMKIFU), 82467 Garmisch-Partenkirchen, Germany
  • apresent address: Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA

Abstract. Semi-arid forests are found to sustain a massive sensible heat flux in spite of having a low surface to air temperature difference by lowering the aerodynamic resistance to heat transfer (rH) – a property called the canopy convector effect (CCE). In this work large-eddy simulations are used to demonstrate that the CCE appears more generally in canopy turbulence. It is indeed a generic feature of canopy turbulence: rH of a canopy is found to reduce with increasing unstable stratification, which effectively increases the aerodynamic roughness for the same physical roughness of the canopy. This relation offers a sufficient condition to construct a general description of the CCE. In addition, we review existing parameterizations for rH from the evapotranspiration literature and test to what extent they are able to capture the CCE, thereby exploring the possibility of an improved parameterization.

Short summary
The canopy convector effect in the context of canopy turbulence was recently introduced by Rotenberg and Yakir (Science, 2010). However, there was a lack of understanding of this phenomenon as a generic feature of canopy turbulence, as we have demonstrated in this paper. Uncertainties of existing parameterizations of canopy aerodynamic resistance to heat transfer are discussed and possible remedies are suggested.