Based on a comprehensive analysis on Sonic Anemometer and gradient data, wind profile radar(WPR) and GPS sounding data of March–August 2008 from the boundary layer(BL) tower observation system at Dali on the southeastern edge of Tibetan Plateau(TP), it is found that the strengths of turbulent kinetic energy(TKE), buoyancy term and shear term depend on vegetation cover in association with local stability and thermodynamic condition. Strong kinetic turbulence appears when near surface layer in neutral condition with the large contribution from shear term. In an unstable condition within near surface layer, the atmospheric turbulent motion is mainly thermal turbulence, as buoyancy term is obviously larger than shear term. Under a stable condition the intermittent turbulence is accompanied by weak shear and buoyancy term, and TKE is significantly less than neutral or instable condition. The study also presents that the buoyancy term contribution at Nyingchi station in the southern slopes of the TP large topography in spring is significantly larger than that at Dali over the southeastern TP edge, reflecting that the thermal turbulence makes an important contribution to convection activity in the southern slopes of TP. Dali station is located in complex terrain with mountain and valley leading to larger kinetic turbulence. From the perspective of interaction of turbulence-convection in different scales, the study revealed that the height of convective boundary layer(CBL) could reach up to 1500–2000 m. TKE, shear term, and buoyancy term in near surface layer have the notable correlations with BL height and local vertical motion. The daytime thermodynamic turbulence effect of heat flux and buoyancy term has an obvious impact on the height of CBL, whereas mechanical turbulence only exerts a less impact. Mechanical turbulence in near surface layer has a significant impact on vertical motion especially in the forenoon with impacting height of 2500–3000 m. The peaks in diurnal variations of shear term and buoyancy term
WANG YinJunXU XiangDeZHAO TianLiangSUN JiHuaYAO WenQingZHOU MingYu
The aquatic eco-environment is significantly affected by temporal and spatial variation of the mixed layer depth(MLD) in large shallow lakes.In the present study,we simulated the three-dimensional water temperature of Taihu Lake with an unstructured grid with a finite-volume coastal ocean model(FVCOM) using wind speed,wind direction,short-wave radiation and other meteorological data measured during 13-18 August 2008.The simulated results were consistent with the measurements.The temporal and spatial distribution of the MLD and the possible relevant mechanisms were analyzed on the basis of the water temperature profile data of Taihu Lake.The results indicated that diurnal stratification might be established through the combined effect of the hydrodynamic conditions induced by wind and the heat exchange between air and water.Compared with the net heat flux,the changes of the MLD were delayed approximately two hours.Furthermore,there were significant spatial differences of the MLD in Taihu Lake due to the combined impact of thermal and hydrodynamic forces.Briefly,diurnal stratification formed relatively easily in Gonghu Bay,Zhushan Bay,Xukou Bay and East Taihu Bay,and the surface mixed layer was thin.The center of the lake region had the deepest surface mixed layer due to the strong mixing process.In addition,Meiliang Bay showed a medium depth of the surface mixed layer.Our analysis indicated that the spatial difference in the hydrodynamic action was probably the major cause for the spatial variation of the MLD in Taihu Lake.
