Flux measurements over heterogeneous surfaces: error estimates and fetch requirements

To examine the effects of inhomogeneity on surface-atmosphere exchange, measurements of the horizontal and vertical fluxes of energy and mass were taken at a plant canopy edge and downwind of it. The magnitude of horizontal advection decreased with distance from the edge, and was also sensitive to atmospheric stability. Fluxes compared well to the results of a higher-order closure model that predicted mean advection and turbulent fluxes at varying distances from the edge in neutral conditions. In addition, even under varying stability regimes, measured horizontal advection was observed to decrease with distance downwind of the edge following a non-dimensional fetch estimated from distance, locally measured turbulent parameters, and mean wind speed.