THE LAGRANGIAN STOCHASTIC-MODEL FOR FETCH AND LATENT-HEAT FLUX ESTIMATION ABOVE UNIFORM AND NONUNIFORM TERRAIN

A Lagrangian stochastic model was used to estimate the fetch and laten t heat flux above a nonuniform grass-covered forest clearing site at t he Duke Forest, in Durham, North Carolina, and an irrigated bare soil patch at the University of California in Davis. The latent heat flux p redictions by the Lagrangian model compared well with eddy correlation flux measurements. In order to apply the Lagrangian model to a nonuni form grass-covered forest clearing, the surface was treated as an imag inary ''equivalent'' uniform terrain subjected to surface roughness an d turbulence statistics (i.e., mean, variance, and covariance) of velo cities and scalars identical to those measured above the nonuniform te rrain. At the irrigated bare soil site the equilibrium distance of the air from dry to wet was well defined, and its influence on the water vapor flux internal boundary layer was considered. In the Lagrangian m odel, five different schemes to account for inhomogeneous turbulent fl ows were compared in terms of estimating scalar fluxes. Our comparison s demonstrate that the five different schemes produce similar scalar f luxes despite the fact that some of them do not satisfy the well-mixed criterion, Also, the analytical solution to the advection-diffusion e quation was used to predict the fetch and latent heat flux under neutr al conditions and compared to the Lagrangian model.