The junction of the eastern Central Asian Fold Belt and the Siberian Platform: deep structure and Mesozoic tectonics and geodynamics

The tectonic structure of the junction of the eastern Central Asian Fold Belt and the Siberian Platform, along with the deep structure of the Earth's crust and lithosphere in this region, has been described on the basis of new geological and geophysical data (seismic, geoelectric, and space-structural studies as well as new-generation geological maps), combined with new interpretation techniques (processing of the previous data by special software). The data suggest the existence of oblique collision during the convergence of the tectonic plates and, correspondingly, tectonic units composing these plates, when the Mongol–Okhotsk paleobasin closed. Such a scenario within the Aldan–Stanovoi Shield is evidenced by areas of syn- and postcollisional magmatism, with their deep-level and geochemical characteristics, and by the presence of a Late Mesozoic fold–thrust zone. Deep “traces” of these tectonomagmatic events, detected in the course of geological and geophysical modeling, are manifested in inclined deep boundaries between the crustal and lithospheric blocks. On the Earth's surface, they correspond to large fault systems: the Dzheltulak, North and South Tukuringra, Gulyui, and Stanovoi. It has been found that the influence of collision decreases northward with distance from the junction of the eastern Central Asian Fold Belt and the Siberian Platform (Dzheltulak and North Tukuringra transcrustal faults).     

变水深对畸形波及其时频能量谱的影响

使用VOF (volume of fluid)方法实现了变化水深条件下畸形波的数值模拟,使用小波分析方法计算模拟结果的时频能量谱,发现变化水深可以加强波浪的非线性相互作用,使转化到高频端的能量更多,产生了不对称程度更大的畸形波.     

Prediction of wave-induced scour depth under submarine pipelines using machine learning approach

The scour around submarine pipelines may influence their stability; therefore scour prediction is a very important issue in submarine pipeline design. Several investigations have been conducted to develop a relationship between wave-induced scour depth under pipelines and the governing parameters. However, existing formulas do not always yield accurate results due to the complexity of the scour phenomenon. Recently, machine learning approaches such as Artificial Neural Networks (ANNs) have been used to increase the accuracy of the scour depth prediction. Nevertheless, they are not as transparent and easy to use as conventional formulas. In this study, the wave-induced scour was studied in both clear water and live bed conditions using the M5’ model tree as a novel soft computing method. The M5’ model is more transparent and can provide understandable formulas. To develop the models, several dimensionless parameter, such as gap to diameter ratio, Keulegan-Carpenter number and Shields number were used. The results show that the M5’ models increase the accuracy of the scour prediction and that the Shields number is very important in the clear water condition. Overall, the results illustrate that the developed formulas could serve as a valuable tool for the prediction of wave-induced scour depth under both live bed and clear water conditions.     

A coupled-mode system with application to nonlinear water waves propagating in finite water depth and in variable bathymetry regions

A non-linear coupled-mode system of horizontal equations is presented, modelling the evolution of nonlinear water waves in finite depth over a general bottom topography. The vertical structure of the wave field is represented by means of a local-mode series expansion of the wave potential. This series contains the usual propagating and evanescent modes, plus two additional terms, the free-surface mode and the sloping-bottom mode, enabling to consistently treat the non-vertical end-conditions at the free-surface and the bottom boundaries. The present coupled-mode system fully accounts for the effects of non-linearity and dispersion, and the local-mode series exhibits fast convergence. Thus, a small number of modes (up to 5–6) are usually enough for precise numerical solution. In the present work, the coupled-mode system is applied to the numerical investigation of families of steady travelling wave solutions in constant depth, corresponding to a wide range of water depths, ranging from intermediate depth to shallow-water wave conditions, and its results are compared vs. Stokes and cnoidal wave theories, as well as with fully nonlinear Fourier methods. Furthermore, numerical results are presented for waves propagating over variable bathymetry regions and compared with nonlinear methods based on boundary integral formulation and experimental data, showing good agreement.     

Depth matters: Microbial eukaryote diversity and community structure in the eastern North Pacific revealed through environmental gene libraries

Protistan community structure was examined from 6 depths (1.5, 20, 42, 150, 500, 880 m) at a coastal ocean site in the San Pedro Channel, California. A total of 856 partial length 18S rDNA protistan sequences from the six clone libraries were analyzed to characterize diversity present at each depth. The sequences were grouped into a total of 259 Operational Taxonomic Units (OTUs) that were inferred using an automated OTU calling program that formed OTUs with approximately species-level distinction (95% sequence similarity). Most OTUs (194 out of 259) were observed at only one specific depth, and only two were present in clone libraries from all depths. OTUs were obtained from 21 major protistan taxonomic groups determined by their closest BLAST matches to identified protists in the NCBI database. Approximately 74% of the detected OTUs belonged to the Chromalveolates, with Group II alveolates making up the largest single group. Protistan assemblages at euphotic depths (1.5, 20 and 42 m) were characterized by the presence of clades that contained phototrophic species (stramenopiles, chlorophytes and haptophytes) as well as consumers (especially ciliates). Assemblages in the lower water column (150, 500 and 800 m) were distinct from communities at shallow depths because of strong contributions from taxa belonging to euglenozoans, acantharians, polycystines and Taxopodida (Sticholonche spp. and close relatives). Species richness (Chao I estimate) and diversity (Shannon index) were highest within the euphotic zone and at 150 m, and lowest for protistan assemblages located in the oxygen minimum zone (500 and 880 m). Multivariate analyses (Bray-Curtis coefficient) confirmed that protistan assemblage composition differed significantly when samples were grouped into shallow (≤150 m) and deep water assemblages (≥150 m).     

海洋温跃层特征值的分析与计算

海洋跃层的分析计算是海洋要素值随深度变化的衍生计算,本文基于实际业务化建设经验,不同于以往大量单站温盐观测资料的跃层特征值提取完全由人工分析判断的工作方法,而是将不等距微分法、垂直梯度法和七点二次平滑等算法融合应用到跃层分析工作中,辅以人机交互模式,实现海洋温跃层特征值信息的快速分析计算和产品制作,可大幅缩减人为工作量...     

1961-2014年青藏高原积雪时空特征及其影响因子

利用青藏高原(下称高原)1961-2014年地面110个气象站积雪深度、积雪日数、气温和降水逐日资料,系统地分析了高原积雪深度和积雪日数时空特征,并进一步探究了高原积雪深度和积雪日数与气候因子和地理因子之间的关系。研究发现:1961-2014年高原年平均积雪深度和积雪日数分别为0.26 cm和23.78 d,空间和季节尺度上分布不均匀,且积雪深度和积雪日数大值并不完全重合;在整体变化趋势上,积雪深度和积雪日数均呈缓慢下降趋势,分别为-0.0080±0.0086 cm·(10a)^-1(p=0.36)和-0.64±0.47 d·(10a)^-1(p=0.17),但在数理统计上不显著,且各站点差异性大;积雪深度和积雪日数在春季、冬季和年表现为“减-增-减”的年代际变化特征,而在秋季为“增-减”的变化特征;气温与积雪深度和积雪日数均有较好的相关性,冬季的降水与积雪深度和积雪日数高度相关;积雪深度和积雪日数随海拔呈增加趋势,积雪日数与纬度也高度相关,但积雪深度与纬度的相关性不明显。     

山东降雪含水比统计特征分析

降雪含水比（snow-to-liquid ratio,SLR）是指积雪深度与降雪融化后等量液体深度（降雪量）的比值,可用来计算积雪深度。山东有两种产生机制不同的降雪,冷流降雪主要分布在山东半岛北部沿海地区,其他类降雪在全省范围均可发生,二者的降雪含水比有明显差异。利用山东122个国家级气象观测站自建站以来至2018年12月的逐12 h降水量、日积雪深度、降水性质、日最高气温及1999—2018年的MICAPS高空、地面图资料,通过限定条件进行质量控制,统计分析了山东不同地区的降雪含水比气候特征,为积雪深度预报提供参考。结果表明：1）山东降雪含水比的变化范围为0.1～3.0 cm·mm-1,全省大部地区多年平均降雪含水比为0.9 cm·mm-1,主要集中在0.3～1.1 cm·mm-1之间;山东半岛北部沿海地区（强冷流降雪区域）的多年平均降雪含水比为1.3 cm·mm-1,主要集中在0.9～2.0 cm·mm-1之间。2）降雪含水比的大小与降雪量等级有关,且存在明显月变化。全省大部地区从中雪至暴雪随着降雪量等级的增大,降雪含水比依次减小;各等级的降雪含水比月最大值均出现在1月或12月,最小值出现在11月或2月;山东半岛北部沿海地区的降雪含水比表现出更为复杂的特征,在以冷流降雪为主的11月—次年1月,中雪、大雪和暴雪的降雪含水比基本相当;2月和3月冷流降雪不明显,降雪含水比表现出与其他地区降雪类似的特征。3）不同天气系统暴雪的降雪含水比有差异。江淮气旋暴雪过程平均降雪含水比为0.69 cm·mm-1,总体上呈现“北大南小,山区大沿海小”分布,中雪、大雪和暴雪的降雪含水比中位数分别为0.8、0.7和0.5 cm·mm-1;回流形势暴雪过程的全省平均降雪含水比为0.67 cm·mm-1,中雪的降雪含水比中位数为0.8 cm·mm-1,大雪和暴雪均为0.6 cm·mm-1;冷流暴雪的降雪含水比明显大于其他两类暴雪,中位数在1.1～1.6 cm·mm-1之间变化,中雪、大雪和暴雪的降雪含水比中位数分别为1.4、1.6和1.3 cm·mm-1。     

民勤绿洲外围不同林龄人工梭梭林的土壤水分特征

 2009年6月到9月,每月中旬在民勤绿洲边缘不同林龄(2 a,5 a,10 a,20 a,30 a)的人工梭梭林内测试不同深度(20 cm,30 cm,50 cm,100 cm,150 cm和200 cm)的土壤含水量变化情况。分析结果表明,不同林龄的梭梭林内土壤含水量与时间和深度有关。土壤表层含水量主要受自然降雨控制,8月底发生比较大的自然降雨后,9月不同林龄梭梭林内20 cm和30 cm的含水量显著高于其他3个月。土壤50 cm以下的含水量比较稳定,当降雨少,土壤表层含水量低时,可以作为梭梭利用的水分来源。在7月和8月,5 a梭梭林内土壤含水量最低,表明梭梭对土壤水分的消耗最多,栽植密度过大,因此,需要间伐减少植株数量才能维持其稳定性。     

Accuracy of kinematic wave and diffusion wave for spatial‐varying rainfall excess over a plane

The kinematic‐wave and diffusive‐wave approximations were investigated for unsteady overland flow resulting from spatially varying rainfall excess. Three types of boundary conditions were adopted: zero flow at the upstream end, and critical flow and zero depth‐gradient at the downstream end. Errors were derived by comparing the dimensionless profiles of the flow depth over the plane with those computed from the dynamic‐wave solution. It was found that the mean errors for both the approximations were independent of the type of rainfall excess distribution for KF₀² > 5, where K is the kinematic‐wave number and F₀ is the Froude number. Therefore, the regions (KF₀², F₀) where the kinematic‐wave and diffusive‐wave solutions would be fairly accurate and for any distribution of spatially varying rainfall, were characterized. The kinematic‐wave approximation was reasonably accurate, with a mean error of less than 5% and for the critical depth at the downstream end, for KF₀² ≥ 20 with F₀ ≤ 1; if the rainfall excess was concentrated in a portion of the plane, the field where the kinematic‐wave solution was found accurate, it was more limited and characterized for KF₀² > 35 with F₀ ≤ 1. The diffusive‐wave solution was in good agreement with the dynamic‐wave solution with a mean error of less than 5%, in the flow depth, for KF₀² ≥ 15 with F₀ ≤ 1; for rainfall excess concentrated in a portion of the plane, the accuracy of the diffusion wave solution was in a region more restricted and defined for KF₀² ≥ 30 with F₀ ≤ 1. For zero‐depth gradient at the downstream end, the accuracy field of the kinematic‐wave was found to be greater and characterized for KF₀² > 10 with F₀ ≤ 1; for rainfall excess concentrated in a portion of the plane, the region was smaller and defined for KF₀² > 15 with F₀ ≤ 1. The diffusive‐wave solution was found accurate in the region defined for KF₀² > 7·5, whereas for rainfall excess concentrated in a portion of the plane, the field of accuracy was for KF₀² > 12·5 with F₀ ≤ 1. The lower limits of the regions, defined on KF₀², can be considered generally valid for both approximations, but for F₀ < 1 smaller lower limits were also characterized. Finally, the accuracy of these approximations was influenced significantly by the downstream boundary condition. Copyright © 2002 John Wiley & Sons, Ltd.