Modelling fluxes and concentrations of CO2, H2O and sensible heat within and above a mountain meadow canopy: a comparison of three Lagrangian models and three parameterisation options for the Lagrangian time scale.

摘要

Two simple analytical Lagrangian and a Lagrangian random walk model, together with three options for the parameterisation of the Lagrangian time scale, are compared in their ability to predict fluxes and scalar concentrations of CO2, H2O and sensible heat within and above a mountain meadow in the eastern Alps. Results indicate that both scalar concentrations and ecosystem fluxes exhibit little sensitivity to the differences between the investigated models and may be predicted satisfactorily by one of the simpler models so long as the source/sink strength is parameterised correctly. Model results also show little sensitivity to the parameterisation of the vertical variation of the Lagrangian time scale, yet the increase of the Lagrangian time scale towards the ground predicted by one of the three investigated parameterisation options resulted in less agreement with measurements as compared to the other two, which assumed the Lagrangian time scale to be either constant with height or to decay towards zero at the ground surface. Correspondence between simulated and measured fluxes and scalar concentrations of CO2, H2O and sensible heat were generally satisfactory, except for shortly after the meadow was cut, when the significant increase of respiratory carbon losses could not be captured by the model.