| Popis: |
Heat transport through short and closed vegetation, such as, grass is modelled by asimple diffusion process. The grass is treated as a homogeneous ``sponge layer'' withuniform thermal diffusivity and conductivity, placed on top of the soil. The temperatureand heat flux dynamics in both vegetation and soil are described using harmonicanalysis. All thermal properties have been determined by optimization againstobservations from the Haarweg station in the Netherlands. Our resultsindicate that both phase and amplitude of soil temperatures can be accuratelyreproduced from the vegetation surface temperature. The diffusion approach requiresno specific tuning to, e.g., the daily cycle, but instead responds to all frequenciespresent in the input data, including quick changes in cloud cover and day-nighttransitions. The newly determined heat flux at the atmosphere-vegetation interface iscompared with the other components of the surface energy balance. The budget iswell-closed, particularly in the most challenging cases with varying cloud cover andduring transition periods. We conclude that the diffusion approach is a promising andphysically consistent alternative to more ad-hoc methods, like ``skin resistance''approaches for vegetation and bulk correction methods for upper soil heat storage.However, more work is needed to evaluate parameter variability and robustness underdifferent climatological conditions. From a numerical perspective, the multi-frequencydescription allows for studying cases where the atmospheric boundary layer and thetop-surface interact on sub-hourly timescales. It would therefore be interesting tocouple the current land-surface description to turbulent resolving methods, such as,large-eddy simulations. |
