理查逊数和晴空颠簸的关系

对切变气流中重力内波的稳定性进行了数值计算，结果表明，判别晴空颠是否发生的临界Ｒｉ数随波长，层结稳定度和基本气流变强度的不同而有所变化，预报业务中用Ｒｉ〈０．２５作为预报晴空的指标易出现空报。     

强对流天气发生前期地面风场特征

根据对华东地区9次强对流天气的地面风场分析发现,强对流的发生发展与锋前暖区的中尺度辐合线有密切关系,与地面中尺度辐合线相伴的扰动辐合值为-0.8×10~(-4)·s~(-1)左右.当有移动的天气系统与其相遇时,交点附近扰动辐合值迅速增大,促使对流迅猛发展且移速加快.辐合线的形成与大尺度背景和特定地形有关.移动的中尺度辐合线与变压风有关而静正辐合线常与露点锋相伴.     

Observational estimation of heat budgets on drifting ice and open water over the Arctic Ocean

It is of major scientific interests to determine the parameters of momentum, heat and vapor exchange in the planetary boundary layer in order to study the effects of ocean-ice-atmosphere interactions and their feedback mechanisms on global climate[1]. Lin…     

Experimental determination of saltating glass particle dispersion in a turbulent boundary layer

A horizontal saltation layer of glass particles in air is investigated experimentally over a flat bed and also over a triangular ridge in a wind tunnel. Particle concentrations are measured by light scattering diffusion (LSD) and digital image processing, and velocities using particle image velocimetry (PIV). All the statistical moments of the particle concentration are determined such as mean concentration, root mean square concentration fluctuations, skewness and flatness coefficients. Over the flat bed, it is confirmed that the mean concentration decreases exponentially with height, the mean dispersion height being a significant length scale. It is shown that the concentration distribution follows quite well a lognormal distribution. Over the ridge, measurements were made at the top of the ridge and in the cavity region and are compared with measurements without the ridge. On the hill crest, particles are retarded, the saltation layer decreases in thickness and concentration is increased. Downwind of the ridge, particle flow behaves like a jet, in particular no particle return flow is observed. Copyright © 2006 John Wiley & Sons, Ltd.     

Turbulence Scale Dependence of the Richardson Constant in Lagrangian Stochastic Models

We investigate the relative dispersion properties of the well-mixed class of Lagrangian stochastic models. Dimensional analysis shows that, given a model in the class, its properties depend solely on a non-dimensional parameter, which measures the relative weight of Lagrangian-to-Eulerian scales. This parameter is formulated in terms of Kolmogorov constants, and model properties are then studied by modifying its value in a range that contains the experimental variability. Large variations are found for the quantity, g* = 2gC₀^{− 1}, where g is the Richardson constant.     

Theorem of turbulent intensity and macroscopic mechanism of the turbulence development

Turbulence is one of the most common nature phenomena in everyday experience, but that is not adequately understood yet. This article reviews the history and present state of development of the turbulence theory and indicates the necessity to probe into the turbulent features and mechanism with the different methods at different levels. Therefore this article proves a theorem of turbulent transpor- tation and a theorem of turbulent intensity by using the theory of the nonequilibrium thermodynamics, and that the Reynolds turbulence and the Rayleigh-Bénard turbulence are united in the theorems of the turbulent intensity and the turbulent transportation. The macroscopic cause of the development of fluid turbulence is a result from shearing effect of the velocity together with the temperature, which is also the macroscopic cause of the stretch and fold of trajectory in the phase space of turbulent field. And it is proved by the observed data of atmosphere that the phenomenological coefficient of turbulent in- tensity is not only a function of the velocity shear but also a function of temperature shear, viz the sta- bility of temperature stratification, in the atmosphere. Accordingly, authenticity of the theorem, which is proved by the theory of nonequilibrium thermodynamics, of turbulent intensity is testified by the facts of observational experiment.     

Large-eddy simulation of plant canopy flows using plant-scale representation

Turbulent flow in a corn canopy is simulated using large-eddy simulation (LES) with a Lagrangian dynamic Smagorinsky model. A new numerical representation of plant canopies is presented that resolves approximately the local structure of plants and takes into account their spatial arrangement. As a validation, computational results are compared with experimental data from recent field particle image velocimetry (PIV) measurements and two previous experimental campaigns. Numerical simulation using the traditional modelling method to represent the canopy (field-scale approach) is also conducted as a comparison to the plant-scale approach. The combination of temporal PIV data, LES and spatial PIV data allows us to couple a wide range of relevant turbulence scales. There is good agreement between experimental data and numerical predictions using the plant-scale approach in terms of various turbulence statistics. Within the canopy, the plant-scale approach also allows the capture of more details than the field-scale approach, including instantaneous gusts that penetrate deep inside the canopy.     

Experimental observation on the characteristics of the near-surface turbulence over the Antarctic ice sheets during the polar day period

Based on the ultrasonic anemometer/thermometer data in the East Antarctic coastal area ice sheets ob-tained first by Chinese scientists, turbulent intensity, kinetic energy and sensible heat of turbulence, surface roughness height drag coefficient and normalized variation were calculated and analysed using the eddy-correlation method. The results show that the values of roughness height and drag coefficient are 4.3 X 10 m and 1.8x 10 -³, respectively. These turbulent parameters have apparent diurnal variations. Project supported by the National Natural Science Foundation of China (Grant No. 49675252).     

Driving Galactic Turbulence by Supernova Explosions

We investigate the general properties of supernova driven interstellar turbulence using local three-dimensional MHD simulations under Galactic conditions. Our model includes the effects of large-scale shear due to Galactic differential rotation, density stratification, compressibility, magnetic fields, heating via supernova explosions and parameterized radiative cooling of the interstellar medium. In addition to investigating isolated supernova explosions we allow for multiple supernovae distributed randomly in the Galactic disc and exponentially in the vertical direction. Single supernova explosions drive a strong shock, the lifetime of which is approximately 2 Myr in our model. This stage is found to be characterized by a kinetic energy spectrum in the diffuse gas with spectral index consistent with k = –2. Large-scale shear and Coriolis force act on the supernova remnant producing some vorticity inside it, but this process was found to be very weak. In the case of multiple supernova explosions, older remnants have an important role causing density fluctuations in the interstellar medium. In this clumpy medium, the propagation velocity of the shock fronts changes due to the changing density, and vorticity is generated. In the absence of these supernova interactions the kinetic energy spectrum shows a relatively wide shock spectrum with spectral index k = –2, but when the supernova interactions become dominant the classical k = –5/3 spectrum is observed.