Canopy source-sink distribution

Several field tests of the IL method have demonstrated that it is a practically useful tool for inferring the canopy source-sink distributions of scalars such as water vapor, heat, CO2, and ammonia. However, there is a continuing need for improvement in the knowledge of the turbulence field in the canopy and its use in determining Dj, and also in the inversion procedure to improve the robustness of the method. 

Katul, G. G., Leuning, R., Kim, )., Denmead, O. T., Miyata, A., and Hara-7.ono, Y. (2001). Estimating CO, source/sink distributions within a rice canopy using higher-order closure models. Boundary-Layer Meleorol. 98, 103- 125. 

Leuning, R., Denmead, O. X, Miyata, A., and Kim, J. (2000). Source-sink distributions of heat, water vapour, carbon dioxide and methane in rice canopies estimated using Lagrangian dispersion analysis. Agric. Forest Meteorol. 104, 233-249. 

For many situations, this is too restrictive and a modification must be made to account for the fact that exchanges between the atmosphere and the canopy occur at levels elevated from the ground surface by plant components. The common procedure is to introduce a quantity called the zero-plane displacement to adjust the level at which momentum, or the variety of scalar quantities, are exchanged. Whereas all levels within the canopy might be active and the various sources or sinks are distributed through the depth of the canopy, they are represented in this case by a single level. The wind profile can then be written ... 

The shortcoming of such descriptions of exchange is that diffusion is not a local phenomenon, as implied by these formulations, and eddy sizes most important to exchange within the canopy can be many times larger than scales associated with the distribution of sources and sinks of heat, water vapour, etc. As an obvious example, gradient diffusion would not permit a secondary maximum in the wind profile in an extensive canopy, because such a profile would require a counter-gradient flux of momentum. 

This chapter has reviewed canopy-scale inverse methods for inferring distributions of sources and sinks from concentration profiles in the air and has further developed these methods for the interpretation of measurements of profiles of isotopic composition. Canopy-scale inverse methods have been placed in context with... 

---