The presence of coherent structures in turbulent shear flows is a great finding in turbulence research,which shows the orderly flows in turbulence which seems fully random.This article analyses the high-speed coherent structure in unstable PBL using the data measured at Pukou,Nanjing.These data include wind velocity measured by the sonic anemometer at the heights of 40 m and 2 m,and the vertical profiles of wind velocity measured with a Doppler wind-profile radar.The authors analyse the fluctuation velocity by employing wavelet transforming at the time scale of 400 s,and the high-speed coherent structure is recognized and located using the threshold value.By comparison with the corresponding wind profiles acquired by radar,these coherent structures satisfy our convention understanding which has long time scales(more than 5 min) and large vertical scales(about thickness of PBL).The nondimensional intervalbetween the coherent structures for the three days is about 6,which means that at the distance of six thickness of PBL,one coherent structure can be found.The wavelet coefficient of vertical fluctuation velocity is correlated with the corresponding wavelet coefficient of horizontal fluctuation velocity,which shows that the downward vertical velocity apparently exists in the high-speed coherent structure,this result is similar to the Gustiness theory in earlier research.Sweep motion and ejection motion are two dominant types of turbulence motion,which transport minus momentum flux.The high-speed coherent structure influences significantly the momentum flux by promoting the sweep motion and restraining the ejection motion.

Convective water-tank is used to model the development of the convective boundary layer on thermal heterogeneous surface.Mosaic-like cover is put on the bottom of the water-tank to achieve thermal heterogeneity.In the convective boundary layer development,temperature profiles were measured on different surface region and with which heat flux profiles are calculated.The results show that normalized heat flux profiles behave the non-linear characteristics,that is,the convex and concave features.Convex and concave features oscillate over time.This is obviously different from the case of homogeneous surface.From heat flux contour map,the oscillation of the overall average heat flux profiles is smaller than that of the uncovered and the covered surface regions.And the oscillation on the uncovered surface region has a higher frequency and greater amplitude.The results show that some turbulence structures of convective boundary layer on thermal heterogeneous surface are quite different from that on the homogeneous surface.The law of the parameters for homogeneous surface can not be applied alike for heterogeneous surface.The experimental results can provide useful reference for numerical simulation and field observations.