Turbulence structure in unstable conditions over various surfaces

A comprehensive study of the turbulent structure of the atmospheric boundar y layer in unstable conditions has been carried out using turbulence data o btained from the Gobi desert, grassland, suburban and urban sites based on the same instrumentation, data acquisition and data processing systems. The normalized standard deviations of u and v over the suburban and urban site s are systematically smaller than those over the Gobi desert and grassland sites. However, the normalized standard deviations of w, temperature theta and humidity q over the suburban and urban sites are quite close to those o ver the Gobi desert and grassland sites. The normalized humidity standard d eviations are quite similar to those of temperature over the grassland and suburban sites. The temperature and humidity spectra are found to be indepe ndent of atmospheric stability in all frequency ranges, but spectra obtaine d from the Gobi desert and grassland sites reveal flatter peaks than those of the suburban and urban sites in the lower frequency range. The normalize d spectral curves of temperature and humidity are independent of atmospheri c stability both at high and low frequencies. The spectral characteristics of humidity over the grassland and suburban sites are similar to those of t emperature, but the humidity spectra over the Gobi desert site are quite di fferent from temperature spectra due to evaporation and/or large eddies in the boundary layer.