Evaluation of the dispersion coefficient for numerical simulations of tropospheric transport

Data of velocity spectra in wave number and frequency space available in literature are analysed to estimate climatological values of the dissipation rate of kinetic energy ε. In the frame of Kolmogorov (1941) theory, the relationship between diffusion coefficient and spectral window is used to determine the diffusion coefficient as a function of resolved scale. To exploit frequency spectrum data with a limited knowledge of flow conditions, a hypothesis on the relationship between the Eulerian time scale and the sampling temporal window was formulated, and the implied empirical constant was determined. Using the obtained values and some recent similarity relationships for the boundary-layer, a parameterisation of ε was adopted to propose an expression of the horizontal dispersion coefficient for different heights and different scales, which is suitable for use in numerical models with special reference to climate applications