Development and testing of Lagrangian models of scalar dispersion in canopies.

摘要

Describing the turbulent dispersion of scalars and momentum within and above plant canopies continues to be an important task in micrometeorology. The aim of this study was to develop and test Lagrangian models for scalar dispersion in plant canopies. This thesis includes two parts: (1) field testing Warland and Thurtell's (2000) one-dimensional Lagrangian dispersion model in terms of the inverse analysis, and (2) developing an approximate two-dimensional Lagrangian solution to the relationship between source strengths and concentration profiles within and above plant canopies.; A multi-port air sampling system was designed to measure CO2 and water vapour profiles within and above canopies, which provided high accurate concentration profile measurements for estimating source/sink distributions and fluxes using Lagrangian dispersion models. This system used minimum volume from manifold to gas analyzer to reduce delay time, and averaging volumes to attenuate turbulent fluctuations of scalar concentrations. Field testing showed that averaging volumes could decrease the mean measurement error (due to partial sampling time) in the measured 30-min mean concentrations of CO 2 and water vapour by 56% and 71%, respectively, for the test period.; The performance of two one-dimensional Lagrangian dispersion models, Warland and Thurtell's model (2000) and localized near-field theory was field tested. The results indicated that the two models were able to predict source/sink distributions and above-canopy fluxes, and their performance was similar and comparable in terms of the above-canopy fluxes. Further, the models' ability to separate soil evaporation from canopy transpiration has also been tested under field conditions.; Finally, a two-dimensional Lagrangian model was derived for relating scalar source strengths and concentration profiles within and above plant canopies. Beginning with an infinite continuous line source, the solution was extended to a canopy source. A new solution is proposed to describe dispersion from near-field to far-field continuously under conditions of local advection by accounting for the effect of advection on concentration gradients for different downwind distances. Model predictions agree well with field (Rider et al., 1963) and wind tunnel experiments (Coppin et al., 1986). The model is able to predict absolute concentration profiles for different fetches for the situation in which the reference concentration is known or the background concentration is available, though field testing of this model is still needed.