Fetch and footprint of turbulent fluxes over vegetative stands with elevated sources

In this study, Raupach's localized near-field (LNF) theory is combined with appropriate parameterizations of the turbulence inside a canopy to investigate how air stability and source configuration influence the flux footprint and flux adjustment with fetch in the roughness sublayer. The model equations are solved numerically. The flux footprint from the LNF prediction is in general more contracted than the prediction based on the inertial sublayer similarity functions. In very unstable conditions, the near-field effect causes the footprint of the elevated canopy source to locate further upwind than that of the ground-level source, and the combined footprint can become negative in situations where the two sources are of opposite sign. The flux footprint and flux adjustment with fetch in the roughness sublayer are sensitive to source configuration and the parameters specifying wind speed and the Lagrangian time scale inside the canopy.