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Stably Stratified Boundary-Layer Flow Over Low Hills: A Comparison of Model Results and Field Data

A linear theory of airflow over low hills andthe MSFD–STAB model are comparedwith published observations made at Cooper'sRidge, north–west of Goulburn inNew South Wales, Australia. The MSFD–STABmodel results show good agreementwith field data in weak to moderate stablystratified flow cases. The originallinear theory overpredicts the wind speed-upratio even in weakly stablecases. After some modification, the agreementis greatly improved.     

Numerical Study on Vortices in the Middle Layer of Flow around a Large Mountain under Rotating Stratified Conditions

Generation of cyclonic vortices in the middle layer of flow around a large mountain like Tibet and Rocky was investigated by means of a 3-D nonhydrostatic meteorological prognostic model. Special attention was paid to the effects of the earth’s rotation and stratification on the vortices detached successively from the slope of a high and large horizontal scale mountain. It was found the successive formation and detachment of such ‘von Karman-like vortices’ occurred in the flow regime at high Rossby numbers Ro and low Froude numbers Fr. It was successfully divided by the criterion of baroclinic instability. This means that if the condition is unstable baroclinically, a lee vortex is destabilized into a three-dimensional one, while under baroclinically stable conditions the lee vortex with vertical axis retains its standing structure and remains long lasting in the middle layer.     

多层软弱夹层边坡岩体破坏机制与稳定性研究

以大量的实际工程为基础,基于Sarma极限平衡法和有限元强度折减法探讨层状岩质边坡在不同岩层倾角θ、边坡坡角β、结构面间距h条件下的安全系数与破坏面位置的变化规律,揭示复杂多层软弱夹层边坡岩体的破坏机制及稳定性特征。结果表明：不同θ条件下边坡岩体失稳机制和破坏面位置不同,随着θ的增大,破坏机制表现为滑移破坏→滑劈破坏→崩塌破坏→倾倒破坏→滑移破坏;当β、h一定时,直立层状边坡的稳定性略大于水平层状边坡,反倾向边坡的稳定性明显大于顺层边坡;β直接影响边坡岩体破坏特征,当β由30°增大至60°时,顺层边坡的安全系数约降低53%;反倾向层状边坡的安全系数约降低40%;h对边坡岩体破坏机制的影响较小,但对稳定性的影响较大,建议工程实践中加强密集结构面岩质边坡的监测和加固工作。     

新型分层抽水管内止水装置的研制

为满足分层抽水试验止水及观测要求,设计加工制做了一种新型管内分层抽水止水装置。此新型止水装置结构简单,方便现场取材及加工制作,且止水效果可靠,克服了以往止水方法存在的缺陷,能有效地隔离上下含水层,防止上下含水层串通,从而能够在同一井孔内实现快速地管内分层止水,保证了分层抽水试验工作的实施。     

基于对地抽样总量控制下的玉米种植面积提取

提出了一种基于统计抽样总量控制下的中高分辨率遥感影像玉米种植面积信息提取方法, 该方法首先利用分层抽样技术对调查目标总体(玉米)进行分层抽样;然后对抽样小区进行目视解译, 反推区域总量真值;最后在总量控制下进行区域目标作物的空间分布提取。以河北省三河市中部地区的部分影像为研究区, 以该区2006-08-21的10m分辨率的SPOT 5多光谱影像为基础数据进行了试验研究。结果表明该方法基于群样本检验的总体精度达到93.8%, Kappa系数达到0.88, 均高于最大似然监督分类结果的精度。另外, 所提出的方     

L波段探空判别云区方法的研究

利用Ka波段毫米波云雷达联合雨滴谱仪、L波段探空和地面常规气象台站等观测资料对四川盆地秋季一次层状云弱降水过程进行观测,分析研究了其宏、微观结构特征及雨滴谱分布特征,并对云中融化层(零度层亮带)进行详细的分析和对比。结果表明：(1)云系内有对流泡,雨强大部分集中在2 mm·h^-1以下,降水峰值与对流泡具有较好的对应关系。(2)降水发生前主要为层状云,云顶高度约为3 km,云底高度约为1.5 km,云中主要以粒径小、相态单一的液相粒子为主; 降水发展期的云系以层状云为主,伴随对流泡发生,层状云顶高度约为4 km,云系内的对流泡云顶最高可达10 km,雷达回波及地形成地面降水,云中有明显的零度层亮带(融化层)现象; 降水消散期的云系变为双层云,下层以层积云为主,云顶高度在4 km以下,以粒径小、相态单一的液相粒子为主,上层云以高积云为主,云底高度约在5 km,云顶高度延伸到8 km以上,以粒径小、相态单一的冰相粒子为主。(3)降水发生前和降水发展期云滴谱呈单峰结构,谱较窄,谱宽在0.312~2.375 mm之间,峰值位于0.437 mm,以小粒子为主,降水消散期为双峰型,峰值位于0.437 mm和1.375 mm之间。降水发展期雨滴谱和数浓度相对更大。(4)层状降水云零度层亮带厚度为200~600 m,不同雷达参量上亮带厚度不同; 退偏振比对零度层亮带最为敏感,最早在垂直廓线上出现亮带信息,是粒子相态变化的重要指标; 亮带厚度与径向速度、谱宽、退偏振比差值相关度很高,但与回波强度差值关系不大。

     

瞬变电磁场的波场变换研究

通过对不同条件下层状介质模型瞬变电磁场数据的波场变换、分析,提高了对瞬变电磁场波场变换物理意义的认识,并总结出若干有价值的规律.指出这种通过数学方法变换出的波场,不仅在形式上满足波动方程,而且在导电介质中也存在"传播"现象,在"传播"过程中,当遇到电性分界面时,也存在"反射"和"透射".这些结论为在瞬变电磁法中,正确合理地引入地震处理解释方法提供了重要的理论依据.     

Asymptotic aspects of the Boussinesq approximation for gases and liquids

Abstract

The asymptotic formulation of the Boussinesq approximation relates the pressure of the fluid to a thermodynamical quantity involving the heat capacity c_Po . In this paper we examine the implications of such a scaling, in particular: (i) the singular degeneracy of the equation of state ρ = ρ* (1 ?α* (T?;T*)) of a liquid: this equation of state is valid only for small values of the coefficient α T*; (ii) in which manner the scaling introduces the Mach number of the flow as a small parameter e for a compressible fluid. The equations at order zero with respect to ? are the same equations for gases and for liquids only if the thermodynamics of the medium is described by using the Brunt-Väisälä frequency instead of the temperature.     

Hydromagnetic waves in a differentially rotating,stratified spherical shell

Abstract

Investigations of an earlier paper (Friedlander 1987a) are extended to include the effect of an azimuthal shear flow on the small amplitude oscillations of a rotating, density stratified, electrically conducting, non-dissipative fluid in the geometry of a spherical shell. The basic state mean fields are taken to be arbitrary toroidal axisymmetric functions of space that are consistent with the constraint of the ‘‘magnetic thermal wind equation''. The problem is formulated to emphasize the similarities between the magnetic and the non-magnetic internal wave problem. Energy integrals are constructed and the stabilizing/destabilizing roles of the shears in the basic state functions are examined. Effects of curvature and sphericity are studied for the eigenvalue problem. This is given by a partial differential equation (P.D.E.) of mixed type with, in general, a complex pattern of turning surfaces delineating the hyperbolic and elliptic regimes. Further mathematical complexities arise from a distribution of the magnetic analogue of critical latitudes. The magnetic extension of Laplace's tidal equations are discussed. It is observed that the magnetic analogue of planetary waves may propagate to the east and to the west.