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91.
92.
强对流天气发生前期地面风场特征 总被引:5,自引:1,他引:5
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. 相似文献
93.
Observational estimation of heat budgets on drifting ice and open water over the Arctic Ocean 总被引:9,自引:0,他引:9
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… 相似文献
94.
1.IntroductionArnol'd(1965,1969)variationalprincipleandapriorestimatemethodisessentiallyageneralizationofLyapunovstabilitymethodforfinite--dimensionaldynamicalsystemsininfinite--dimensionalones,andhestudiedthenonlinearstabilityof2--dimensionalincompressibleidealfluidmotionbyuseofthismethod,andestablishedtwotheoremswhichareArnol,d'sfirsttheoremandArnol'd'ssecondtheorem.Eversincethe1980's,manyscientistshavebeenworkingonthissubject,Holmetal.(1985);MclntyreandShepherd(1987);Zeng(1989);Muetal.(1… 相似文献
95.
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. 相似文献
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98.
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. 相似文献
99.
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. 相似文献
100.
Wusi Yue Marc B. Parlange Charles Meneveau Weihong Zhu René van Hout Joseph Katz 《Boundary-Layer Meteorology》2007,124(2):183-203
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. 相似文献