Numerical estimations of the horizontal advection of scalars inside canopies

A thorough knowledge of the exchange of momentum, heat, moisture, and CO2 between forests and the atmosphere is essential in order to understand the role of forest ecosystems in the global atmospheric CO2 budget. In micrometeorology, the horizontal transport of momentum, heat, and moisture resulting from surface inhomogeneities is known as local advection. Because ideal homogeneous surface is rarely seen at the earth’s surface, neglect of advection due to surface inhomogeneity can lead to systematic errors in net ecosystem exchange (NEE) measurements. The local advection of momentum and scalars is numerically investigated by a 2-dimensional higher-order turbulence closure model which includes equations for the mean quantities of momentum and scalar, turbulent fluxes of 2nd and 3rd moments, and turbulent kinetic energy. The relative contributions from the turbulent flux, mean advection, flux divergence, and turbulent transport are compared for momentum and scalar in streamwise and vertical directions, respectively. They are compared to outputs from 1st-order closure (K-theory) model also.