SUMMARYSpectra have been measured over a variety of types of complex terrain: on tops of hills and escarpments, Differences between spectra over many types of complex terrain, and over uniform terrain, can be When air moves over terrain with changed characteristics, then(1) for wavelengths very short relative to the fetch over the new terrain, the spectral densities are in equilibrium with the new terrain.(2) for wavelengths long compared to this fetch, spectral densities remain unchanged if the ground is horizontal, and decrease when the flow is uphill, for the longitudinal velocity component only. Since vertical-velocity spectra contain relatively less low wavenumber energy than horizontal-velocity over land downstream of a water surface, and over rolling terrain.explained by these hypotheses: spectra, energetic vertical-velocity fluctuations tend to be in equilibrium with local terrain.
SUMMARYAn 'effective' roughness length is defined for use over heterogeneous terrain as the roughness length which homogeneous terrain would have to give the correct surface stress over a given area. A method is suggested to compute geostrophic drag coefficient, wind-contour angle and surface heat flux, given this roughness length, latitude, geostrophic wind speed and insolation or ground-air temperature differences.
SUMMARYObservations from many sources have been brought together to study the relationship between the ratio of standard deviation of vertical velocity to friction velocity, and z/L where z is the height and L the Monin-Obukhov length. A good compromise for this relationship is : This equation has been combined with theoretical expressions for the wind profile to derive a nomogram for the standard deviation of vertical angle as function of z/L and z/zo, where zo is the roughness length.
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