On The Dynamical Content Of Lagrangian Stochastic Models In The Well-Mixed Class

It is shown how the correspondence between Lagrangian stochasticmodels and second-moment closures of the scalar-flux equation can be exploited to distinguishbetween Lagrangian stochastic models in the well-mixed class. It is found that physically realisticclosures of the scalar-flux equation correspond to Lagrangian stochastic models that have non-zero`spin' and so produce spiralling tracer-particle trajectories, whilst `zero-spin'models correspond to the isotropic-production model of scalar-fluxes.Lagrangian stochastic models consistent with rapid distortion theory and Speziale's transformation rule for the Reynolds stressequations in the extreme limit of two-dimensional turbulence are also shown to have non-zero spin.The residual non-uniqueness associated with satisfaction of thewell-mixed condition and the specification of mean spin is shown to be related to the helicity oftracer-particle trajectories. Investigations are also made of the influence upon turbulent dispersion oftime-dependent spin and of mean rotations of the fluctuating Lagrangian acceleration vector(i.e., second-order spin).     

广州市GPS控制网的设计特色和技术要点

介绍了广州市GPS控制网的设计特色、技术要点和实际效果，该控制网的实践对大型控制网布测具有一定的指导作用。     

Some aspects of the role of intergranular fluids in the compositional evolution of metamorphic rocks

Minerals that react with each other during the progressive evolution of metamorphic terranes are not always in physical contact. As such, an “intergranular fluid” could play a major role in element transfer and chemical evolution. However, the nature of this fluid and its specific role remains somewhat elusive. Recent experiments in our laboratory shed some light on the behavior of such a fluid. Here we present a simple mathematical model which accounts for diffusion within crystals and fluid, solubility in the fluid and mass balance between the various reservoirs. The model elucidates the nature of element exchange between two minerals via the mediation of an intergranular fluid. It is shown that a coupling of thermodynamics and kinetics controls the evolution of the system and the concentration of an element in the intergranular fluid is a key parameter of interest. The results have important implications for standard tools of metamorphic petrology such as geothermometers and barometers, geospeedometry and the closure of isotopic systems. For example, homogeneity of mineral grains may be a poor criterion for equilibrium and the rim compositions of minerals showing diffusion zoning may be out of equilibrium with distant exchange partners, even in the presence of a fluid in which transport is fast.     

小尺度深凹地形PBL结构的数值模拟研究

本大建立了一个针对小尺度深凹地形（深凹露天矿）使用的三维非静力的诊断模式。模式中采用能量（E－）闭合方案，取细网络，具有甚高的空间分辨率。利用该模式充分分析了露天矿边界层的结构特征。数值试验的结果表明．初始地面风速，初始的风速垂直切变，露天矿的采深及边坡用的大小等因素对复环流有较大影响。     

Effect of three different boundary-layer parameterisations in a regional atmospheric model on the simulation of summer monsoon circulation

Bulk, first-order and turbulent kinetic energy (TKE) closure schemes are used to parameterise the boundary-layer physics in a high resolution, limited area model. The model was used to simulate the summer monsoon circulations over India. The domain selected included the monsoon trough over northern India, a region of mesoscale convection. A monsoon depression was present at the time of the simulation. The results indicate that the TKE closure scheme combined with the Monin–Obukhov surface-layer similarity relation provided the best 48-hour simulation of the circulation and the rainfall associated with the monsoon depression.     

Oxygen isotope exchange and closure temperatures in cooling rocks

Retrograde exchange of oxygen isotopes between minerals in igneous and metamorphic rocks by means of diffusion is explored using a finite difference computer model, which predicts both the zonation profile of δ¹⁸O within grains, and the bulk δ¹⁸O value of each mineral in the rock. Apparent oxygen isotope equilibrium temperatures that would be observed in these rocks are calculated from the δ¹⁸O values of each mineral pair within the rock. In systems which cool linearly from a sufficiently high temperature or at a low enough cooling rate, such that the final oxygen isotope values are not dependent upon the initial oxygen isotope values ('slow cooling'), the apparent oxygen isotope temperature derived for a rock composed of a single mineral pair can be shown to be simply related to the Dodson closure temperatures ( T _c) for the two phases and the mode of the rock. Adding a third phase into a system which undergoes 'slow' cooling will cause the apparent temperature derived for the two minerals already present to differ from the simple relationship for a two-phase system. In some systems oxygen isotope reversals can be developed. If cooling is not 'slow', then the mineral δ¹⁸O values resulting from cooling will be partly dependent upon the initial temperature of the system concerned. The model successfully simulates the mineral δ¹⁸O values that are often observed in granitic rocks. Application of the model will help in assessing the validity of oxygen isotope thermometry in different geological settings, and allows quantitative prediction of the oxygen isotope fractionations that are developed in cooling closed systems.     

二阶闭合模式在污染气象学中的某些应用

本文采用二阶闭合的湍流边界层模式,进行一系列数值试验以模拟边界层中连续线源的扩散状况。试验表明:无论在稳定的或不稳定的边界层中,高源的扩散能力都低于低源;在稳定层中,粗糙地表上的大气扩散能力高于光滑表面;在相同风速和地表净辐射情况下,粗糙表面上的大气扩散能力反而低于光滑表面;对流边界层中存在反梯度输送,因而K理论的应用受到限制。试验还表明,修正的Kazanski-Monin参数可能比Monin-Obukhov长度更能反映大气的扩散能力。     

A STUDY OF 1.5-ORDER CLOSURE TURBULENCE MODEL

Based on turbulence theory,a 1.5-order closure turbulence model is established.The model incorporating with theground surface energy budget equation is constructed by means of a vertical one-dimensional(1-D)40-levelgrid-mesh.The numerical results reveal the 24-h evolution of the clear planetary boundary layer comparing with theWangara boundary layer data of days 33—34.The model also takes into account some physical processes of radiativetransfer and baroclinicity,revealing some important characteristics observed in the boundary layer,especially for theevolution of the mixed layer and low-level jet.The calculated results are in good agreement with the observational data.On the other hand,we also run the high-resolution model of the planetary boundary layer in the Mesoscale Model Ver-sion 4(MM4)with the same physical processes and initial conditions.The results show that the high-resolution modelcan not reveal those important characteristics as the 1.5-order closure model did.In general,it is shown that the 1.5-or-der closure turbulence model based on turbulence theory is better in rationality and reality.     

Overwash occurrence consequent on morphodynamic changes following lagoon outlet closure on a coarse clastic barrier

The reduction in sediment volume of an ebb-tide delta, as a consequence of lagoon outlet closure on a coarse clastic barrier in southeast Ireland, initiated a sequence of beachface and barrier changes downdrift. Elimination of sediment supply to the ebb-delta caused a cessation of downdrift longshore swash bar welding, and led to beach volume reductions which in turn allowed a temporal sequence of beach and nearshore morphodynamic domains to develop. These domains then controlled the sedimentation regime of the barrier adjacent to the old outlet. A temporal sequence of (a) dissipative barrier; (b) reflective barrier; and (c) inner reflective (barrier face)/outer dissipative (subtidal) wave regimes match respectively periods of (a) barrier crest build up by crestal dune development; (b) barrier crest instability (barrier width increasing, barrier height decreasing) due to rhythmic overwash; and (c) a return to barrier crest stability with limited aeolian accretion. Two barriers at different stages in this sequence are discussed.