Articles | Volume 21, issue 6
Research article
20 Jun 2017
Research article |  | 20 Jun 2017

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

Tirtha Banerjee, Frederik De Roo, and Matthias Mauder

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.