非典型周期和气候突变的识别与判定          下载免费PDF全文

秦建国 《水文》2020,40(1):23-28

通过两种新方法分析了无锡站降水年际变化的突变性、周期性等特征,揭示了旱涝演化的自然规律。研究表明,1934、1978、2013年是我国近现代气候突变的临界点,这是旱涝演化的自然选择;无锡站年际降水的观测历史可分成四个特征不同的时段,每个时段节点对应的都是一次气候突变;气候突变会改变年际降水序列的一致性,分段法研究可以大幅度降低模拟难度、提高预测效率。发现并确认了3个气候突变点,实现了超长缺测中断期(13a)旱涝趋势的精确插补,完成了无锡站近百年降雨序列的周期性分析与旱涝趋势预测模拟,研究成果改变了近现代气候历史无法细分的现状。  相似文献   

陕西黑河流域地下水水化学特征     

王晓艳 《中国沙漠》2019,39(4):168-176

2017年在秦岭黑河流域7个采样点进行地下水样品采集。通过综合分析、Gibbs图、Piper三角图、主要离子比值法、主成分分析法得出黑河地下水化学成分的特点、水化学类型及其成因。结果表明：阳离子的主要组成成分是Ca²⁺，HCO₃^-是阴离子的主要组成成分，黑河流域地下水化学类型为HCO₃^-- Ca²⁺和SO₄^2--HCO₃^--Ca²⁺型。Gibbs图分析得出该地下水化学离子组成受岩石风化作用控制；Piper三角图、主要离子比值法、主成分分析及相关分析表明，地下水化学组分主要受方解石、白云岩等碳酸盐岩矿物的风化溶解，同时伴有硫酸溶解碳酸盐岩，受硅酸盐岩的溶解控制作用较小。  相似文献   

黄河干流头道拐河段凌汛期小流量过程变化及其影响因素研究     

全栋  李超  路新川  史小红  杨朝霞 《冰川冻土》2020,42(2):620-628

黄河干流内蒙古段河道冬季流凌封河期， 河道水量除一部分转化为冰量外， 很大一部分转化为槽蓄水量而贮存在河道中， 导致下游头道拐河段出现小流量过程， 上游河道流量转化为槽蓄水量和贮存的冰量越大， 小流量持续时间越长， 开河期发生凌汛洪水风险越高。通过对1998 - 2016年头道拐站凌讯期流量变化过程分析， 重新界定了小流量上限阈值为330 m³·s^-1， 并且以此值为标准进行小流量过程研究， 分别采用R/S极差分析法、 Fourier变换分析法对近年来小流量过程变化特征进行分析； 结合非线性概率Logit模型和Probit模型对小流量过程的影响因素进行讨论。结果表明： 小流量持续天数变化呈现缩短趋势； 同时， 小流量过程与上游相对来水之间变化关系显著且过程同步， 而滞后于河道槽蓄水量变化过程； 通过Logit模型和Probit模型分析各影响因素变化时相应小流量持续时间变化的响应概率大小， 明确河道冰流量是小流量过程第一影响因素， 气温条件是小流量过程的决定因素， 首封位置和相对来水量是小流量过程重要影响因素。  相似文献   

Flexural deformation controls on Late Quaternary sediment dispersal in the Garo-Rajmahal Gap,NW Bengal Basin     

Jean-Louis Grimaud  Celine Grall  Steven Goodbred  Michael S. Steckler  Ryan Sincavage  Jennifer L. Pickering  Chris Paola  Leonardo Seeber  Md. Saddam Hossain 《Basin Research》2020,32(5):1242-1260

Subsurface deformation is a driver for river path selection when deformation rates become comparable to the autogenic mobility rate of rivers. Here we combine geomorphology, soil and sediment facies analyses, and geophysical data of the Late Quaternary sediments of the central Garo-Rajmahal Gap in Northwest Bengal to link subsurface deformation with surface processes. We show variable sedimentation characteristics, from slow rates (<0.8 mm/year) in the Tista megafan at the foot of the Himalaya to nondeposition at the exposed surface of the Barind Tract to the south, enabling the development of mature soils. Combined subsidence in the Tista fan and uplift of the Barind Tract are consistent with a N-S flexural response of the Indian plate to loading of the Himalaya Mountains given a low value of elastic thickness (15–25 km). Provenance analysis based on bulk strontium concentration suggests a dispersal of sediment consistent with this flexural deformation—in particular the abandonment of the Barind Tract by a Pleistocene Brahmaputra River and the current extents of the Tista megafan lobes. Overall, these results highlight the control by deeply rooted deformation patterns on the routing of sediment by large rivers in foreland settings.  相似文献   

Obtaining the distribution of quiescent periods directly from the power spectral densities of Sea waves     

《Applied Ocean Research》2019

There is a growing practical interest in the ability to increase the sea states at which marine operations can be safely undertaken by exploiting the quiescent periods that are well known to exist under a wide range of sea conditions. While the actual prediction of quiescent periods at sea for the control of operations is a deterministic process, the long term planning of future maritime tasks that rely on these quiescent periods is a statistical process involving the anticipated quiescence properties of the forecasted sea conditions in the geographical region of interest. It is in principle possible to obtain such data in tabular form either large scale simulation or from field data. However, such simulations are computationally intensive and libraries of appropriate field data are not common. Thus, it is clearly attractive to develop techniques that exploit standard wave spectral models for describing the quiescence statistics directly from such spectra. The present study focuses upon such techniques and is a first step towards the production of a computationally low-cost quiescence prediction tool and compares its efficacy against simulations. Two significant properties emerge for a large class of wave spectral models that encompasses the ubiquitous Neumann and Pierson Moskowitz or Bretschneider forms. Firstly, the auto-correlation function of the wave profile that are required to produce the quiescence property can be obtained analytically in terms of standard special functions. This considerably reduces the computational cost making desktop computer-based planning tools a reality. Secondly, for each class of these parametric spectra, the probability of a given number of consecutive wave heights (normalised to the significant wave heights) less than some critical value is in fact independent of absolute wave height. Thus, for a broad class of practically interesting wave spectra all that is required to obtain the statistical distribution of the quiescent periods is simple rescaling.  相似文献   

晋西北地区表层土壤粒度与地球化学元素组成   总被引：1，自引：1，他引：0  

李继彦  周玲  刘益  张倩  蔡莹莹  张宝贵 《中国沙漠》2019,39(5):155-162

对晋西北地区表层土壤的物质组成进行研究，可以明确其物质来源、沉积环境及化学风化特征。选择区内表层土壤（深度0、10、20 cm）及其附近的河流沉积物，进行粒度和化学元素组成测试。结果表明：（1）晋西北地区表层土壤粒度组成以黏土和粉沙为主，且有自地表向下粗颗粒组分含量增加的趋势。（2）常量化学元素组成以SiO₂、Al₂O₃、CaO、Fe₂O₃为主，其余元素含量均较低。化学元素组成模式表明研究区内表层土壤物质与黄土高原腹地黄土有相同的物质源区，黄河河流沉积物对其贡献不大。（3）晋西北表层土壤的CIA值为52.70~57.89，平均54.06，说明它们的化学风化程度较低，处于早期的脱Na、Ca阶段。这是由于研究区地理位置比洛川更靠北，气温和降水量均低于洛川，降水量与兰州相差不大，但是年平均气温和年温差比兰州低。该研究明确了晋西北地区表层土壤的物质组成特征，为区域潜在沙漠化危害防治提供了数据支撑。  相似文献   

Deterioration processes affecting prehistoric rock art engravings in granite in NW Spain          下载免费PDF全文

J.S. Pozo‐Antonio  T. Rivas  F. Carrera  L. García 《地球表面变化过程与地形》2018,43(11):2435-2448

Prehistoric rock art sites are endangered despite conservation efforts. The lack of scientific documentation regarding weathering agents affecting rock art and the absence of specific diagnostic protocols hinder the development of conservation strategies. The aim of this research was to investigate active deterioration processes in a granite petroglyph site located in Mougás (Galicia, NW Spain) by characterizing the granite, conducting a geotechnical study of the outcrop and describing and analysing the main weathering processes. Two main deterioration factors were identified. First, water favours block disjunction at the massif scale and causes pitting and surface erosion at the millimetre scale that affects the readability of the engravings. Second, high temperatures associated with wildfires cause mineral transformations that increase the susceptibility of the rock to weathering. Identifying deterioration factors is a first step in developing appropriate preventive conservation measures, which should aim to reduce rock contact time with water (technically affordable in the short term) and to reduce the probability of wildfire occurrence (technically more complex and possibly with longer‐term results). Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

Insights into agricultural influences and weathering processes from major ion patterns          下载免费PDF全文

Robert van Geldern  Peter Schulte  Michael Mader  Alfons Baier  Johannes A.C. Barth  Tobias R. Juhlke  Kern Lee 《水文研究》2018,32(7):891-903

Karst areas and their catchments pose a great challenge for protection because fast conduit flow results in low natural attenuation of anthropogenic contaminants. Studies of the hydrochemistry of karst sources and river solutes are an important tool for securing and managing water resources. A study of the geochemical downriver evolution of the Wiesent River and its tributaries, located in a typical karst terrain, revealed unexpected downstream decreases of nitrate with maximum mean values of 30 mg/L at the source to minimum values of 18 mg/L near the river mouth. This trend persisted over the length of the river even though increased agricultural activities are evident in the downstream section of the catchment. This pattern is caused by fertilizer inputs via diffusive and fast conduits flow from karst lithology in the upstream area that may have reached the river's source even from beyond the hydrological catchment boundaries. Further downstream, these influences became diluted by tributary inputs that drain subcatchments dominated by claystone and sandstone lithologies that increased potassium and sulphate concentrations. Our findings indicate that bedrock geology remains the dominant control on the major ion chemistry of the Wiesent River and that agricultural influences are strongest near the headwaters despite increased land use further downstream, due to long‐term storage and accumulation in karst aquifers. This feature may not be unique to the Wiesent River system, as carbonates cover significant portions of the Earth's surface and subsequent work in other river systems could establish whether such patterns are ubiquitous worldwide.  相似文献   

南海北部海域油气资源调查技术及其应用研究——震源子波检测及模拟分析          下载免费PDF全文

曾宪军  翟继锋  韦成龙 《海洋技术学报》2019,38(2)

在野外采集中考察气枪的稳定性以及室内进行确定性子波反褶积处理,都要求能够获得气枪阵列的实时远场子波。从震源子波检测方法出发,阐述了近场子波采集、幅值转换及记录流程,并列举出实测近场子波时需要考虑解决的问题;接着介绍了震源远场子波的获取方法和主要途径;震源近场子波及远场子波的实测方案,检测震源子波所需的仪器设备和采集技术方法。文中分析了气枪子波的气泡干扰问题,虚反射与后续气泡震荡间的关系以及吸收衰减对子波的影响,并根据实测远场子波,对齐氏和范氏两种气体模型进行了模拟效果对比,结果表明:采用范氏气体模型所模拟的子波与实际子波更为吻合,模拟出的气枪的子波波形、振幅大小、气泡周期上,与业界通用的Nucleus软件的模拟结果吻合较好,在后续的使用中将继续优化。  相似文献   

Relating the depth of the water table to the depth of weathering     

M.I. Lebedeva  S.L. Brantley 《地球表面变化过程与地形》2020,45(9):2167-2178

Weathering of bedrock creates and occludes permeability, affecting subsurface water flow. Often, weathering intensifies above the water table. On the contrary, weathering can also commence below the water table. To explore relationships between weathering and the water table, a simplified weathering model for an eroding hillslope was formulated that takes into account both saturated and unsaturated subsurface water flow (but does not fully account for changes in dissolved gas chemistry). The phreatic line was calculated using solutions to mathematical treatments for both zones. In the model, the infiltration rate at the hill surface sets both the original and the eventual steady-state position of the water table with respect to the weathering reaction front. Depending on parameters, the weathering front can locate either above or below the water table at steady state. Erosion also affects the water table position by changing porosity and permeability even when other hydrological conditions (e.g. hydraulic conductivity of parent material, infiltration rate at the surface) do not change. The total porosity in a hill (water storage capacity) was found to increase with infiltration rate (all else held constant). This effect was diminished by increasing the erosion rate. We also show examples of how the infiltration rate affects the position of the water table and how infiltration rate affects weathering advance. Published 2020. This article is a U.S. Government work and is in the public domain in the USA  相似文献