A vertical sounding of severe haze process in Guangzhou area

We detected a severe haze process in Guangzhou area with lidar and microwave radiometer, performed an inversion to get boundary layer height by wavelet covariance transform, and analyzed the correlation between meteorological factors of boundary layer and visibility from the perspective of dynamical and thermodynamic structures. Our results indicate that the boundary layer height shows significant daily changes, consistent with ground visibility variation. During the cleaning process, the boundary layer height exceeded 1 km; during severe haze, the height was only 500 m. Temperature gradient of 50–100 m, which was 30 h lag, was remarkably correlated with visibility, with the correlation coefficient of 0.77. High layer visibility(255 m) and low layer stability were significantly anticorrelation, and the maximum anticorrelation coefficient was up to-0.76 in cleaning days and-0.49 in haze days. In the related boundary layer meteorological factors, surface ventilation coefficient was linearly correlated with ground visibility, with the greatest correlation coefficient of 0.88. The correlation coefficients of boundary layer height, ground wind velocity, relative humidity and ground visibility were 0.76, 0.67, and-0.77, respectively. There was a strong correlation between different meteorological factors. The dominant meteorological factor during this haze process was surface ventilation coefficient. In the area without boundary layer height sounding, ground visibility and wind velocity could be used to estimate boundary layer height.     

A nonlinear,resistive boundary layer in rotating hydromagnetic flow

A new nonlinear boundary layer in rotating hydromagnetic flows is presented. The purpose of this layer is to provide a smooth transition between the magnetic field at a rigid, electrically insulating boundary and that far from the boundary. The boundary layer problem is solved in a cylindrical geometry, assuming that the variables obey the hydromagnetic analog of the von Karman similarity. The primary momentum balance within this boundary layer is between pressure, Coriolis and hydromagnetic forces; the viscous and nonlinear inertia forces are unimportant. Diffusion of the magnetic field is balanced by advection where the advecting fluid flow is induced by the action of the hydromagnetic body forces within the boundary layer. The structure of the layer depends upon a single parameter which measures the strength of the normal magnetic field. Steady solutions are presented and their uniqueness and temporal stability are analyzed. The relevance of this layer to the core of the Earth is discussed. It is estimated that this boundary layer would be at least as thick as one tenth of the core radius if it exists within the core.     

A RECONCILIATION OF MATHEMATICAL MODELS FOR SPONTANEOUS MINERALIZATION POTENTIALS1

Two methods for computing spontaneous mineralization potentials in the region external to the source body are reviewed. The first of these is a long-established technique in which the causation is assumed to be a distribution of simple current source on the boundary of the mineralization. The second is a more recent technique which assumes a surface distribution of current dipole moment (double layer) along the boundary of the source body. The former technique is a special case of a more general spontaneous potential (SP) model in which the source is a density of current dipole moment (current polarization) distributed throughout the mineralization. As far as the potentials in the region external to the source body are concerned this current polarization can be simply related to an equivalent double layer source function, i.e. the potential discontinuity produced over the boundary of the mineralization by an equivalent double layer model. This simple relationship suggests an integral equation technique for the exact numerical solution of boundary value problems appropriate to the polarization model for spontaneous mineralization potentials. The technique is applied to exploring the justification of interpreting mineralization self-potentials by the traditional approach.     

大气边界层湍流的动力非平稳性的验证

首次用验证时间序列中是否存在动力非平稳性的一种简单图示方法——space time index法来分析大气边界层湍流的动力平稳性特征.本文以取自淮河流域和威斯康星森林下垫面条件下的三维高精度风速和温度、湿度湍流脉动资料对大气边界层湍流的平稳性特征进行了分析.结果表明space time index方法能有效地检验大气边界层湍流信号中是否存在动力平稳性.另外,均匀下垫面条件（水稻田）及复杂下垫面条件（森林）下的大气边界层湍流信号中几乎都存在动力非平稳性,大气湍流动力学非平稳性可能是边界层湍流信号相当普遍具有的一种特性.大气边界层湍流中的间歇性和相干结构使得其非平稳性图形的特征不同于一般时间序列非平稳性图形的“V”型特征;森林下垫面条件下的湍流信号比相对均匀下垫面（水稻田）下的湍流信号更有组织性,相干结构更强.     

Application of a perfectly matched layer in seismic wavefield simulation with an irregular free surface

Recently, an effective and powerful approach for simulating seismic wave propagation in elastic media with an irregular free surface was proposed. However, in previous studies, researchers used the periodic condition and/or sponge boundary condition to attenuate artificial reflections at boundaries of a computational domain. As demonstrated in many literatures, either the periodic condition or sponge boundary condition is simple but much less effective than the well‐known perfectly matched layer boundary condition. In view of this, we intend to introduce a perfectly matched layer to simulate seismic wavefields in unbounded models with an irregular free surface. We first incorporate a perfectly matched layer into wave equations formulated in a frequency domain in Cartesian coordinates. We then transform them back into a time domain through inverse Fourier transformation. Afterwards, we use a boundary‐conforming grid and map a rectangular grid onto a curved one, which allows us to transform the equations and free surface boundary conditions from Cartesian coordinates to curvilinear coordinates. As numerical examples show, if free surface boundary conditions are imposed at the top border of a model, then it should also be incorporated into the perfectly matched layer imposed at the top‐left and top‐ right corners of a 2D model where the free surface boundary conditions and perfectly matched layer encounter; otherwise, reflections will occur at the intersections of the free surface and the perfectly matched layer, which is confirmed in this paper. So, by replacing normal second derivatives in wave equations in curvilinear coordinates with free surface boundary conditions, we successfully implement the free surface boundary conditions into the perfectly matched layer at the top‐left and top‐right corners of a 2D model at the surface. A number of numerical examples show that the perfectly matched layer constructed in this study is effective in simulating wave propagation in unbounded media and the algorithm for implementation of the perfectly matched layer and free surface boundary conditions is stable for long‐time wavefield simulation on models with an irregular free surface.     

A comprehensive physical pattern of land-air dynamic and thermal structure on the Qinghai-Xizang Plateau

According to the boundary layer observations of three stations (Garze, Damxung and Qamdu) and relevant earth satellite, radiosonde and surface observations during the intensive observational period (IOP) of the second Tibetan (Qinghai-Xizang) Plateau Experiment of atmospheric science (TIPEX), the land-air physical process and dynamic model on the Tibetan Plateau were comprehensively analyzed in this study. The dynamic characteristics of boundary layer and the rules of turbulent motion on the plateau were illustrated. The characteristics of distributions of wind speed and direction with mutiple-layer structure and deep convective mixed layer on the plateau, the strong buoyancy effect in turbulent motion on the plateau on which the air density is obviously smaller than on the plain, and the Ekman spiral and its dynamic pump effect of the plateau deep boundary layer have been found. The local static distribution of water vapor and the horizontal advection of water vapor in the plateau boundary layer were studied. The abnomal thermodynamic structure on the plateau surface and boundary layer, including the plateau strong radiation phenomenon and strong heating source characteristics of the middle plateau, was also analyzed. The authors synthesized the above dynamic and thermodynamic structures of both surface and boundary layers on the plateau and posed the comprehensive physical model of the turbulence and convective mixture mechanism on the plateau boundary layer. The characteristics of formation, development and movement for convective cloud cluster over the plateau influencing floods in the Yangtze River area of China were studied. The conceptual model of dynamic and thermodynamic structures of turbulent motion and convective plume related to the frequent occurrence of "pop-corn-like" cloud system is given as well.     

非均匀灌溉棉田能量平衡特征研究

运用国际能量平衡实验(EBEX-2000)的湍流、净辐射和土壤观测资料,运用涡动相关法分析了非均匀灌溉引起的热内边界层发展条件下近地层感热、潜热通量特征,并对有无灌溉两种条件下的能量闭合度进行了对比分析.在计算感热、潜热通量过程中,分别将Schotanus订正和Webb订正纳入了考虑范围,研究了两种订正方法对计算湍流热通量的影响.研究结果发现,由于非均匀灌溉生成的热内边界层使得近地层感热通量受到抑制,潜热通量出现波动,该现象在8.7 m比2.7 m 更为显著.非均匀灌溉导致的热内边界层的存在使得近地层能量闭合度偏低,能量平衡比率约为0.65;而没有热内边界层存在时,近地层能量平衡比率约为0.70.本实验中,Schotanus订正使得感热通量显著减小,其订正量日平均值约为-8 W/m²,占净辐射的近4%;Webb订正量日平均值约为2 W/m²,对能量平衡的影响较小.     

Broadband Plasma Waves In The MagnetopauseAnd Polar Cap Boundary Layers

Boundary layers occurring in the magnetosphere can support a wide spectrumof plasma waves spanning a frequency range of a few mHz to tens of kHz andbeyond. This review describes the main characteristics of the broadband plasma waves observed in the Earth's low-latitude magnetopause boundary layer (LLBL), in the polar cap boundary layer (PCBL), and the possible generation mechanisms. The broadband waves at the low-latitude boundary layer are sufficiently intense to cause the diffusion of the magnetosheath plasma across the closed magnetospheric field lines at a rate rapid enough to populate and maintain the boundary layer itself. The rapid pitch angle scattering of energetic particles via cyclotron resonant interactionswith the waves can provide sufficient precipitation energy flux to the ionosphere to create the dayside aurora. In general, the broadband plasma waves may play an important part in the processes of local heating/acceleration of the boundary layer plasma.     

A Raman lidar to measure water vapor in the atmospheric boundary layer

A new multi-telescope scanning Raman lidar designed to measure the water vapor mixing ratio in the atmospheric boundary layer for a complete diurnal cycle with high resolution spatial (1.25 m) and temporal (1 s) resolutions is presented. The high resolution allows detailed measurements of the lower atmosphere and offers new opportunities for evaporation and boundary layer research, atmospheric profiling and visualization. This lidar utilizes a multi-telescope design that provides for an operational range with a nearly constant signal-to-noise ratio, which allows for statistical investigations of atmospheric turbulence. This new generation ground-based water vapor Raman lidar is described, and first observations from the Turbulent Atmospheric Boundary Layer Experiment (TABLE) are presented. Direct comparison with in-situ point measurements obtained during the field campaign demonstrate the ability of the lidar to reliably measure the water vapor mixing ratio. Horizontal measurements taken with time are used to determine the geometric characteristics of coherent structures. Vertical scans are used to visualize nocturnal jet features, layered structures within a stably stratified atmosphere and the internal boundary layer structure over a lake.     

Effect of the oceanic lithosphere velocity on free convection in the asthenosphere beneath mid-ocean ridges

The paper presents results obtained in experiments on a horizontal layer heated from below in its central part and cooled from above; the layer models the oceanic asthenosphere. Flow velocity and temperature profiles are measured and the flow structure under boundary layer conditions is determined (at Rayleigh numbers Ra > 5 × 10⁵). The flow in the core of a plane horizontal layer heated laterally and cooled from above develops under conditions of a constant temperature gradient averaged over the layer thickness. The flow core is modeled by a horizontal layer with a moving upper boundary and with adiabatic bounding surfaces under conditions of a constant horizontal gradient of temperature. Exact solutions of free convection equations are found for this model in the Boussinesq approximation. Model results are compared with experimental data. Temperature and flow velocity ranges are determined for the boundary layer regime. Based on the experimental flow velocity profiles, an expression is found for the flow velocity profile in a horizontal layer with a mobile upper boundary heated laterally and cooled from above. Free convection velocity profiles are obtained for the asthenosphere beneath a mid-ocean ridge (MOR) with a mobile lithosphere. An expression is obtained for the tangential stress at the top of the asthenosphere beneath an MOR and the total friction force produced by the asthenospheric flow at the asthenosphere-lithosphere boundary is determined.     

Formation of the thermal-driven boundary jet in an f-plane mesoscale basin

The paper adopts an f-plane quasi-geostrophic inertial model without linearization to investigate the perturbation temperature, boundary jet and upwelling (downwelling) in an idealized rectangular basin, under the consideration of west side friction layer and heat conservation. There is net heat input on the upper surface and equal quality heat dissipation on the west boundary, and without heat exchange on other boundaries, then the heat is conservation in the whole basin. Results show that there is thermal front due to denseness of the perturbation temperature in the west side boundary, the perturbation pressure and flow field are reversal on the upper layer and bottom layer. On the bottom layer, the west coastal current is northward, and the maximum perturbation pressure center is on the west, however, on the upper layer, the east coastal current is southward, and the maximum perturbation pressure center is on the east. There is strong vertical flow in narrow western boundary layer, and also in the central zone. The effect of different upper thermal forcings is also studied, and it can be concluded that there is always temperature denseness and boundary jet near the west boundary, and the appearance of flow field reversal, but the distribution of vertical flow is rather different.     

边界层参数化方案对边界层热力和动力结构特征影响的比较

本文利用高分辨率中尺度WRF模式,通过改变边界层参数化方案进行多组试验,评估该模式对美国北部森林地区边界层结构的模拟能力,同时比较了五种不同边界层参数化方案模拟得出的边界层热力和动力结构.结果表明：除个别方案外,配合不同边界层方案的WRF模式都能成功模拟出白天对流边界层强湍流混合特征和夜间稳定边界层内强逆温、逆湿和低空急流等热力和动力结构.非局地YSU、ACM2方案在白天表现出强的湍流混合和卷夹,相比于局地MYJ、UW方案,模拟的对流边界层温度更高、湿度更低、混合层高度更高、感热通量更大,更接近实际观测,这表明在不稳定层结下考虑非局地大涡输送更为合理,但局地方案在风速和风向的预报上存在一定优势.TEMF方案得到的白天局地湍流混合强度为所有方案中最弱,混合层难以发展,无法体现对流边界层内气象要素垂直分布均匀的特点.对于夜间稳定边界层的模拟,不同参数化方案之间的差异较小,但是YSU方案在一定程度上高估了机械湍流,导致局地湍流混合偏强,从而影响了其对稳定边界层的模拟能力.     

Power-law velocity profile in turbulent boundary layers: An integral reynolds-number dependent solution

Geophysical flows of practical interest encompass turbulent boundary layer flows. The velocity profile in turbulent flows is generally described by a log- or a power-law applicable to certain zones of the boundary layer, or by wall-wake law for the entire zone of the boundary layer. In this study, a novel theory is proposed from which the power-law velocity profile is obtained for the turbulent boundary layer flow. The new power-law profile is based on the conservation of mass and the skin friction within the boundary layer. From the proposed theory, analytical expressions for the power-law velocity profile are presented, and their Reynolds-number dependency is highlighted. The velocity profile, skin friction coefficient and boundary layer thickness obtained from the proposed theory are validated by the reliable experimental data for zero-pressure gradient turbulent boundary layers. The expressions for Reynolds shear stress and eddy viscosity distributions across the boundary layer are also obtained and validated by the experimental data.     

Efficient seismic analysis for nonlinear soil-structure interaction with a thick soil layer

The direct finite element method is a type commonly used for nonlinear seismic soil-structure interaction(SSI) analysis. This method introduces a truncated boundary referred to as an artificial boundary meant to divide the soilstructure system into finite and infinite domains. An artificial boundary condition is used on a truncated boundary to achieve seismic input and simulate the wave radiation effect of infinite domain. When the soil layer is particularly thick, especially for a three-dimensional problem, the computational efficiency of seismic SSI analysis is very low due to the large size of the finite element model, which contains an whole thick soil layer. In this paper, an accurate and efficient scheme is developed to solve the nonlinear seismic SSI problem regarding thick soil layers. The process consists of nonlinear site response and SSI analysis. The nonlinear site response analysis is still performed for the whole thick soil layer. The artificial boundary at the bottom of the SSI analysis model is subsequently relocated upward from the bottom of the soil layer(bedrock surface) to the location nearest to the structure as possible. Finally, three types of typical sites and underground structures are adopted with seismic SSI analysis to evaluate the accuracy and efficiency of the proposed efficient analysis scheme.     

Capturing the residence time boundary layer—application to the Scheldt Estuary

At high Peclet number, the residence time exhibits a boundary layer adjacent to incoming open boundaries. In a Eulerian model, not resolving this boundary layer can generate spurious oscillations that can propagate into the area of interest. However, resolving this boundary layer would require an unacceptably high spatial resolution. Therefore, alternative methods are needed in which no grid refinement is required to capture the key aspects of the physics of the residence time boundary layer. An extended finite element method representation and a boundary layer parameterisation are presented and tested herein. It is also explained how to preserve local consistency in reversed time simulations so as to avoid the generation of spurious residence time extrema. Finally, the boundary layer parameterisation is applied to the computation of the residence time in the Scheldt Estuary (Belgium/The Netherlands). This timescale is simulated by means of a depth-integrated, finite element, unstructured mesh model, with a high space–time resolution. It is seen that the residence time temporal variations are mainly affected by the semi-diurnal tides. However, the spring–neap variability also impacts the residence time, particularly in the sandbank and shallow areas. Seasonal variability is also observed, which is induced by the fluctuations over the year of the upstream flows. In general, the residence time is an increasing function of the distance to the mouth of the estuary. However, smaller-scale fluctuations are also present: they are caused by local bathymetric features and their impact on the hydrodynamics.     

Impact of soil moisture heterogeneity length scale and gradients on daytime coupled land‐cloudy boundary layer interactions

Using a coupled large‐eddy simulation–land surface model framework, the impact of two‐dimensional soil moisture heterogeneity on the cloudy boundary layer under varied free‐atmosphere stabilities is investigated. Specifically, the impacts of soil moisture heterogeneity length scale and heterogeneity in terms of soil moisture gradients on micrometeorological states, surface fluxes, boundary layer characteristics, and cloud development are examined. The results show that mesoscale circulations due to surface heterogeneity in soil moisture play an important role in transferring water vapour within the boundary layer and in regulating cloud distribution at the entrainment zone, which, in turn, provides feedbacks on boundary layer/surface energy budgets. The initial domain‐averaged soil moisture is identical for all homogenous and heterogeneous cases; however, the soil moisture heterogeneity in gradient and length scale between dry and wet regions has a significant impact on the estimates of near‐surface micrometeorological properties and surface fluxes, which further affect the boundary layer states and characteristics. Both liquid water potential temperature and liquid water mixing ratio increase with an increasing soil moisture gradient, whereas the amount of specific humidity decreases. Heterogeneity length scale and free atmosphere stability also amplify these impacts on the boundary layer structure and cloud formation. In a low atmospheric stability condition that potentially allows for a deeper boundary layer and a higher entrainment rate, cloud base height and cloud thickness significantly increase as the soil moisture gradient and length scale increase. Analysis to differentiate the influences of surface heterogeneity type (i.e. length scale vs gradient) shows that in general soil moisture gradient provides a larger impact than heterogeneity length scale, although the heterogeneity length scale is large enough to initiate circulation features responsible for differences in the coupled system between homogeneous and heterogeneous soil moisture cases. Copyright © 2012 John Wiley & Sons, Ltd.     

The effect of an interface boundary layer on the resonance properties of a buried structure

This paper presents a model for the analysis of the diffraction of plane waves at a cavity in an infinite homogeneous linear elastic medium supported by a segmented lining. An elastic boundary layer is introduced between the cavity lining and the infinite medium. The boundary layer is simulated by ‘elastic boundary conditions’ in which the stress is proportional to the relative displacement of the lining and of the surrounding medium boundary. A closed‐form analytical solution of the problem was obtained using the Fourier–Bessel series, the convergence of which was proven. It was shown that the number of series terms required to obtain a desired level of accuracy can be determined in advance. Using amplitude–frequency response analysis it was shown that the boundary layer produces additional ‘pseudo‐resonance’ frequencies that depend on the layer properties. These frequencies are almost identical to the eigenvalues obtained from the simple analysis of a segmented elastically supported lining. Copyright © 2003 John Wiley & Sons, Ltd.     

逆时偏移计算中的边界处理分析及应用

在地震资料的处理中,逆时偏移方法可以实现复杂构造高精度成像,但计算量和存储量两大问题影响了该方法的实际应用.逆时偏移算法中的边界处理方式的优化可以大大减少存储量,本文讨论了记录波场边界信息的吸收边界和随机边界这两种方法的计算效率和成像效果,提出了吸收边界中只记录边界范围内未衰减单层波场的方法并通过数值实验验证了其可行性,选择了不同的边界策略应用于模型数据和实际资料的处理.结果表明:记录单层波场边界信息的吸收边界的成像效果同传统存储波场历史的方式几乎无差别,但要额外存储每个时刻的波场边界信息;随机边界不需要额外存储波场信息,但会带来边界漫反射影响和计算区域的增加;记录单层波场边界可以明显减少存储量,并且不影响成像效果.