Surface-layer characteristics in the stable boundary layer with strong and weak winds

An extensive meteorological dataset obtained from the plume validation experiment conducted by the Electric Power Research Institute (EPRI) at Kincaid during 1980-1981 is analysed for studying the characteristic differences in the surface-layer parameters in strong and weak wind stable conditions. The surface-layer parameters are computed using the similarity functions phi(m) and phi(h) proposed by Beljaars and Holtslag. The weak winds are characterized using the geostrophic wind speed as well as the wind speed at the 10-m level. The surface fluxes are found to be finite in weak wind conditions. Empirical formulations for the eddy diffusivities of momentum (K-M) and heat (K-H), and drag (C-D) and heat exchange (C-H) coefficients, as power law functions of the bulk Richardson number (Ri(B)), are proposed under both strong and weak wind conditions. Results are close to those based on observations taken from the Indian Institute of Technology low wind diffusion experiment, the Land surface processes experiment, the Hanford diffusion experiment, the Cabauw field experiment and the Cooperative Atmospheric Surface Exchange Study 1999 (CASES-99) experiment. In addition, the fluxes obtained from the proposed empirical relations are in good agreement with those based on similarity theory as well as the turbulence measurements taken from the CASES-99 experiment.