Modelling Fluxes and Concentrations of CO 2 , H 2 O 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 timescale, are compared in their ability to predict fluxes and scalar concentrationsof CO2, H2O and sensible heat within and above a mountain meadowin the eastern Alps. Results indicate that both scalar concentrations and ecosystemfluxes exhibit little sensitivity to the differences between the investigated modelsand may be predicted satisfactorily by one of the simpler models so long as thesource/sink strength is parameterised correctly. Model results also show littlesensitivity to the parameterisation of the vertical variation of the Lagrangiantime scale, yet the increase of the Lagrangian time scale towards the groundpredicted by one of the three investigated parameterisation options resulted inless agreement with measurements as compared to the other two, which assumedthe Lagrangian time scale to be either constant with height or to decay towardszero at the ground surface. Correspondence between simulated and measuredfluxes and scalar concentrations of CO2, H2O and sensible heat weregenerally satisfactory, except for shortly after the meadow was cut, when thesignificant increase of respiratory carbon losses could not be captured by themodel.