Different Turbulent Regimes and Vertical Turbulence Structures of the Urban Nocturnal Stable Boundary Layer

Turbulence in the nocturnal boundary layer(NBL)is still not well characterized,especially over complex underlying surfaces.Herein,gradient tower data and eddy covariance data collected by the Beijing 325-m tower were used to better understand the differentiating characteristics of turbulence regimes and vertical turbulence structure of urban the NBL.As for heights above the urban canopy layer(UCL),the relationship between turbulence velocity scale(VTKE)and wind speed(V)was consistent with the“HOckey-Stick”(HOST)theory proposed for a relatively flat area.Four regimes have been identified according to urban nocturnal stable boundary layer.Regime 1 occurs where local shear plays a leading role for weak turbulence under the constraint that the wind speed V<VT(threshold wind speed).Regime 2 is determined by the existence of strong turbulence that occurs when V>VT and is mainly driven by bulk shear.Regime 3 is identified by the existence of moderate turbulence when upside-down turbulence sporadic bursts occur in the presence of otherwise weak turbulence.Regime 4 is identified as buoyancy turbulence,when V>VT,and the turbulence regime is affected by a combination of local wind shear,bulk shear and buoyancy turbulence.The turbulence activities demonstrated a weak thermal stratification dependency in regime 1,for which within the UCL,the turbulence intensity was strongly affected by local wind shear when V<VT.This study further showed typical examples of different stable boundary layers and the variations between turbulence regimes by analyzing the evolution of wind vectors.Partly because of the influence of large-scale motions,the power spectral density of vertical velocity for upsidedown structure showed an increase at low frequencies.The upside-down structures were also characterized by the highest frequency of the stable stratifications in the higher layer.

Observation of Stable Marine Boundary Layer by Shipborne Coherent Doppler Lidar and Radiosonde over Yellow Sea

Shipborne observations obtained with the coherent Doppler lidar(CDL)and radiosonde during 2014 campaign were used to study the structure of marine boundary layer in the Yellow Sea.Vertical wind profiles corrected for ship motion was used to derive higher-order statistics,showing that motion correction is required and significant for turbulence analysis.During a day with weak mesoscale activity,a complexed three-layer structure system was observed.The lowest layer showed a typical stable boundary layer structure feature.An aerosol layer with abrupt variation in wind speed and relative humidity always appeared at the middle layer,the formation of which may be due to Kelvin-Helmholz instability.The top layer encountered a dramatic change in wind direction,which may result from the warm advection from the Eurasian continent on the basis of backward trajectory analysis.Furthermore,the MABL height in stable regime was derived from potential temperature,CDL signal-to-noise ratio(SNR)and CDL vertical velocity variance,respectively.The stable boundary layer(SBL)height in SBL can be derived from the inversion layer of potential temperature profile,and the mixing height in SBL can be retrieved from the vertical velocity variance gradient method.Neither the SBL height nor the mixing height is in agreement with the height retrieved from CDL SNR gradient method because of different definition and criterion.One of the limitations of SNR gradient method for MABL retrieval is that it is easier to be affected by the lofted decoupled aerosol layer,where the retrieved result is less suitable.Finally,the higher-order vertical velocity statistics within the marine stable boundary layer were investigated and compared with the previous studies,and different turbulence mechanisms have an important effect on the statistics deviation.

Construction Technology and Quality Control of Double Layer Continuous Paving of Cement Stabilized Macadam Base

The construction method of continuous paving of the upper and lower base of the water stable macadam base can improve the construction efficiency,overcome the quality problems of the traditional layered paving of the upper and lower base,such as untimely curing,slow construction,poor interlayer bonding,contraction joint and interlayer,so as to ensure the construction quality of the water stable macadam.It is also the promotion and application of new technology.

P(VDF-HFP)-poly(sulfur-1,3-diisopropenylbenzene) functional polymer electrolyte for lithium–sulfur batteries

Lithium–sulfur(Li–S)battery as a high-energy density electrochemical energy storage system has attracted many researchers’attention.However,the shuttle effect of Li–S batteries and the challenges associated with lithium metal anode caused poor cycle performance.In this work,the organosulfide poly(sulfur-1,3-diisopropenylbenzene)(PSD)was prepared as cathode material and additive of P(VDFHFP)polymer electrolyte(P(VDF-HFP)).It was verified that P(VDF-HFP)polymer electrolyte with 10%PSD(P(VDF-HFP)-10%PSD)showed a higher ionic conductivities than that of liquid electrolyte up to2.27×10-3 S cm-1 at room temperature.The quasi-solid-state Li-S batteries fabricated with organosulfide cathode material PSD and P(VDF-HFP)based functional polymer electrolyte delivered good cycling stability(780 m Ah g-1 after 200 th cycle at 0.1 C)and rate performance(613 m Ah g-1 at 1 C).The good cycling performance could be attributed to the synergistic effect of components,including the interaction between polysulfides and polymer main chain in the organosulfide cathode,the sustained organic/inorganic hybrid stable SEI layer formed by polymer electrolyte additive PSD,the improved cathode/electrolyte interface and the good affinity between P(VDF-HFP)based functional polymer electrolyte and Li metal surface.This strategy herein may provide a new route to fabricate high-performance Li–S batteries through the organosulfide cathode and functional polymer electrolyte.

ON SIMILARITY AND THE TURBULENT STRUCTURE IN THE STABLE BOUNDARY LAYER

In the stably stratified boundary layer,the vertical flux profiles for momentum and heat can be obtained from an atmospheric boundary layer model which includes parameterization of the long-wave radiation,In addi- tion,the Monin-Obukhov similarity theory can be extended to the whole boundary layer by using the local tur- bulent scales L(z),U_*(z)and 0_*(z)in place of surface layer scales.The similarity predictions are in good agreement with observational data.