防震减灾网络宣传工作不容忽视--网上一则热帖带来的启发     

孙春仙  周加新  雷利 《国际地震动态》2006,(5):37-41

本文结合我国互联网使用现状和网络对现实生活的影响,对网络在地震宣传方面的重要作用进行论证,提高决策人员和管理人员对地震专业网站建设的重视度。  相似文献   

A Large-Eddy Simulation and Lagrangian Stochastic Study of Heavy Particle Dispersion in the Convective Boundary Layer   总被引：4，自引：1，他引：4  

Xuhui Cai  Rui Zhang  Yan LI 《Boundary-Layer Meteorology》2006,120(3):413-435

Large-eddy simulation and Lagrangian stochastic dispersion models were used to study heavy particle dispersion in the convective boundary layer (CBL). The effects of various geostrophic winds, particle diameters, and subgrid-scale (SGS) turbulence were investigated. Results showed an obvious depression in the vertical dispersion of heavy particles in the CBL and major vertical stratification in the distribution of particle concentrations, relative to the passive dispersion. Stronger geostrophic winds tended to increase the dispersion of heavy particles in the lower CBL. The SGS turbulence, particularly near the surface, markedly influenced the dispersion of heavy particles in the CBL. For reference, simulations using passive particles were also conducted; these simulation results agreed well with results from previous convective tank experiments and numerical simulations.  相似文献   

Tangling Turbulence and Semi-Organized Structures in Convective Boundary Layers     

T. Elperin  N. Kleeorin  I. Rogachevskii  S. S. Zilitinkevich 《Boundary-Layer Meteorology》2006,119(3):449-472

A new mean-field theory of turbulent convection is developed based on the idea that only the small-scale region of the spectrum is considered as turbulence, whereas its large-scale part, including both regular and semi-organized motions, is treated as the mean flow. In the shear-free regime, this theory predicts the convective wind instability, which causes the formation of large-scale semi-organized motions in the form of cells. In the presence of wind shear, the theory predicts another type of instability, which causes the formation of large-scale semi-organized structures in the form of rolls and the generation of convective-shear waves propagating perpendicular to the convective rolls. The spatial characteristics of these structures, such as the minimum size of the growing perturbations and the size of perturbations with the maximum growth rate, are determined. This theory might be useful for understanding the origin of large-scale cells and rolls observed in the convective boundary layer and laboratory turbulent convection  相似文献   

An Intercomparison of Large-Eddy Simulations of the Stable Boundary Layer   总被引：2，自引：27，他引：2  

Robert J. Beare  Malcolm K. Macvean  Albert A. M. Holtslag  Joan Cuxart  Igor Esau  Jean-Christophe Golaz  Maria A. Jimenez  Marat Khairoutdinov  Branko Kosovic  David Lewellen  Thomas S. Lund  Julie K. Lundquist  Anne Mccabe  Arnold F. Moene  Yign Noh  Siegfried Raasch  Peter Sullivan 《Boundary-Layer Meteorology》2006,118(2):247-272

Results are presented from the first intercomparison of large-eddy simulation (LES) models for the stable boundary layer (SBL), as part of the Global Energy and Water Cycle Experiment Atmospheric Boundary Layer Study initiative. A moderately stable case is used, based on Arctic observations. All models produce successful simulations, in as much as they generate resolved turbulence and reflect many of the results from local scaling theory and observations. Simulations performed at 1-m and 2-m resolution show only small changes in the mean profiles compared to coarser resolutions. Also, sensitivity to subgrid models for individual models highlights their importance in SBL simulation at moderate resolution (6.25 m). Stability functions are derived from the LES using typical mixing lengths used in numerical weather prediction (NWP) and climate models. The functions have smaller values than those used in NWP. There is also support for the use of K-profile similarity in parametrizations. Thus, the results provide improved understanding and motivate future developments of the parametrization of the SBL.  相似文献   

Statistics of Scalar Fields in the Atmospheric Boundary Layer Based on Large-Eddy Simulations. Part II: Forced Convection     

Zbigniew Sorbjan 《Boundary-Layer Meteorology》2006,119(1):57-79

Forced convection in a quasi-steady atmospheric boundary layer is investigated based on a large-eddy simulation (LES) model. The performed simulations show that in the upper portion of the mixed layer the dimensionless (in terms of mixed layer scales) vertical gradients of temperature, humidity, and wind velocity depend on the dimensionless height z/z _i and the Reech number Rn. The peak values of variances and covariances at the top of the mixed layer, scaled in terms of the interfacial scales, are functions of the interfacial Richardson number Ri. As a result expressions for the entrainment rates, in the case when the interfacial layer has a finite depth, and a condition for the presence of moistening or drying regimes in the mixed layer, are derived. Profiles of dimensionless scalar moments in the mixed layer are proposed to be expressed in terms of two empirical similarity functions F _m and F _i , dependent on dimensionless height z/z _i , and the interfacial Richardson number Ri. The obtained similarity expressions adequately approximate the LES profiles of scalar statistics, and properly represent the impact of stability, shear, and entrainment. They are also consistent with the parameterization proposed for free convection in the first part of this paper.  相似文献   

广西厚皮甜瓜气候条件分析   总被引：11，自引：0，他引：11  

陈丹范万新  陈豫梅 《广西气象》2006,27(2):27-29

针对厚皮甜瓜生产的气象条件，结合广西的气候特点，提出广西厚皮甜瓜生产的气候条件分析，为厚皮甜瓜在广西的生产发展提出一些建议。  相似文献   

Simulation of a Stably Stratified Atmospheric Boundary Layer Using One-Dimensional Turbulence     

Alan R. Kerstein  Scott Wunsch 《Boundary-Layer Meteorology》2006,118(2):325-356

One-dimensional turbulence (ODT) is a single-column simulation in which vertical motions are represented by an unsteady advective process, rather than their customary representation by a diffusive process. No space or time averaging of mesh-resolved motions is invoked. Molecular-transport scales can be resolved in ODT simulations of laboratory-scale flows, but this resolution of these scales is prohibitively expensive in ODT simulations of the atmospheric boundary layer (ABL), except possibly in small subregions of a non-uniform mesh.Here, two methods for ODT simulation of the ABL on uniform meshes are described and applied to the GABLS (GEWEX Atmospheric Boundary Layer Study; GEWEX is the Global Energy and Water Cycle Experiment) stable boundary-layer intercomparison case. One method involves resolution of the roughness scale using a fixed eddy viscosity to represent subgrid motions. The other method, which is implemented at lower spatial resolution, involves a variable eddy viscosity determined by the local mesh-resolved flow, as in multi-dimensional large-eddy simulation (LES). When run at typical LES resolution, it reproduces some of the key high-resolution results, but its fidelity is lower in some important respects. It is concluded that a more elaborate empirically based representation of the subgrid physics, closely analogous to closures currently employed in LES of the ABL, might improve its performance substantially, yielding a cost-effective ABL simulation tool. Prospects for further application of ODT to the ABL, including possible use of ODT as a near-surface subgrid closure framework for general circulation modeling, are assessed.  相似文献   

Maximal Overlap Wavelet Statistical Analysis With Application to Atmospheric Turbulence     

Charles R. Cornish  Christopher S. Bretherton  Donald B. Percival 《Boundary-Layer Meteorology》2006,119(2):339-374

Statistical tools based on the maximal overlap discrete wavelet transform (MODWT) are reviewed, and then applied to a dataset of aircraft observations of the atmospheric boundary layer from the tropical eastern Pacific, which includes quasi-stationary and non-stationary segments. The wavelet methods provide decompositions of variances and covariances, e.g. fluxes, between time scales that effectively describe a broadband process like atmospheric turbulence. Easily understood statistical confidence bounds are discussed and applied to these scale decompositions, and results are compared to Fourier methods for quasi-stationary turbulence. The least asymmetric LA(8) wavelet filter yields coefficients that exhibit better uncorrelatedness across scales than the Haar filter and is better suited for decomposition of broadband turbulent signals. An application to a non-stationary segment of our dataset, namely vertical profiles of the turbulent dissipation rate, highlights the flexibility of wavelet methods.  相似文献   

An approximate analytical solution for the deposition of heavy particles released from an elevated line source   总被引：1，自引：1，他引：1  

T. Bouvet  J. D. Wilson 《Boundary-Layer Meteorology》2006,119(1):1-18

This work re-examines and further develops an analytical solution for the deposition swath of heavy particles released in the atmosphere from an elevated source over uniform terrain, correcting the particle diffusivity for the crossing trajectory effect. The revised (approximate) analytical solution proves to be accurate within 20% over a wide range of micrometeorological conditions and particle size, despite its neglect of the turbulence component of the deposition flux. It compares very satisfactorily with experimental data and with the simulations of a Lagrangian stochastic model, provided the variable U(H)/w _g ≤7 (ratio of the mean horizontal wind speed at source height to the particle settling velocity). In this domain of validity, simple formulae relating the statistics of the deposition swath to U(H)/w _g are derived.  相似文献   

黄河源区新构造运动对生态环境恶化的影响   总被引：7，自引：0，他引：7  

张森琦李永国  尚小刚辛元红王占昌  石维栋庄永成 周金元 《地质通报》2006,25(1):213-220

基于黄河源区1:25万生态环境地质调查新获得的大量实际资料,通过分析和研究发现,黄河源区早更新世-中更新世处于走滑伸展的大陆动力学背景,在整体隆升中,形成断块山与拉分盆地,湖泊广布;晚更新世,大陆动力学机制过渡为挤压收缩,在整体抬升中,断块山显著崛起,湖盆萎缩、变形;全新世,大陆动力学环境反转为走滑挤压,持续隆升,黄河扩展源头到达本区,扎陵湖、鄂陵湖外泄,闭流盆地水环境转向开放.近代,特别是20世纪70年代以来,新构造活化与寒冻风化岩屑坡扩大、沙质荒漠化蔓延、湖泊和沼泽湿地萎缩、区域地下水位下降、源区黄河频繁断流、生态环境日益恶化响应关系密切.因此,新构造运动在黄河源区生态环境恶化中起主导作用,而其他因素则起到促进与加速的作用.  相似文献