Stormflow threshold behaviour in a subtropical mountainous headwater catchment during forest recovery period     

Lezhang Wei  Zhijun Qiu  Guangyi Zhou  Tsuyoshi Kinouchi  Yu Liu 《水文研究》2020,34(8):1728-1740

Forest ecohydrological feedbacks complicate the threshold behaviour of stormflow response to precipitation or wetting conditions on a long-term scale (e.g. several years). In this study, the threshold behaviours in an evergreen-deciduous mixed forested headwater catchment in southern China were examined during 2009–2015, when damaged vegetation was recovering after the great 2008 Chinese ice and snowstorm. The non-uniqueness of the thresholds and the slow and rapid responses of stormflow at the outlet of the catchment in different hydro-climate datasets with different maximum values of gross precipitation (P) and sums of precipitation and antecedent soil moisture index (P + ASI) were assessed. The thresholds of P and P + ASI required to trigger stormflows (i.e. ‘generation thresholds’) and the transition from slow to rapid responses of stormflow (i.e. ‘rise thresholds’) were compared both seasonally and annually. The results indicated significant differences in the analysed datasets, highlighting the need to compare thresholds with care to avoid misinterpretation. Seasonal variations in threshold behaviours in the catchment suggested that vegetation canopy interception contributed to higher rise thresholds, and wetter conditions resulted in higher runoff sensitivity to precipitation during the growing and rainy seasons. Furthermore, the generation thresholds were higher in the dormant season, possibly due to drier soil moisture conditions in the near-channel areas. During the vegetation recovery period, the annual generation thresholds increased, however the rise thresholds did not exhibit a similar trend. The rapid stormflow response above the threshold decreased, possibly due to transpiration and interception of the recovered vegetation. However, the slow stormflow response to small rainfall events below the thresholds was higher in wetter years but lower in drier years, suggesting that the total water input dominated the stormflow response during small rainfall events. In conclusion, the seasonal and annual variations in threshold behaviours highlight that vegetation recovery and hydro-climatic conditions had a notable impact on the stormflow response.  相似文献   

Microseism Variations in Response to Antarctic Seasonal Changes in Sea Ice Extent     

XU Xiaoqing  LIN Jianmin  FANG Sunke 《中国地震研究》2020,34(2):264-284

The temporal and spatial distributions of Antarctic sea ice play important roles in both the generation mechanisms and the signal characteristics of microseisms. This link paves the way for seismological investigations of Antarctic sea ice. Here we present an overview of the current state of seismological research about microseisms on Antarctic sea ice. We first briefly review satellite remote-sensing observations of Antarctic sea ice over the past 50 years. We then systematically expound upon the generation mechanisms and source distribution of microseisms in relation to seismic noise investigations of sea ice, and the characteristics of Antarctic microseisms and relationship with sea ice variations are further analyzed. We also analyze the continuous data recorded at seismic station BEAR in West Antarctica from 2011 to 2018 and compare the microseism observations with the corresponding satellite remote-sensing observations of Antarctic sea ice. Our results show that:(1) the microseisms from the coastal regions of West Antarctica exhibit clear seasonal variations, SFM with maximum intensities every April-May and minimum intensities around every October-November; while DFM intensities peak every February-March, and reach the minimum around every October. Comparatively, the strong seasonal periodicity of Antarctic sea ice in better agreement with the observed DFM; and (2) microseism decay is not synchronous with sea ice expansion since the microseism intensity is also linked to the source location, source intensity (e.g., ocean storms, ocean wave field), and other factors. Finally, we discuss the effect of Southern Annular Mode on Antarctic sea ice and microseisms, as well as the current limitations and potential of employing seismological investigations to elucidate Antarctic sea ice variations and climate change.  相似文献   

强震作用下铁路隧道横通道交叉结构抗震措施研究   总被引：1，自引：0，他引：1       下载免费PDF全文

申玉生  陈政  周鹏发  罗宁宁  张熙  杨佳奇 《地震工程学报》2020,42(1):182-193

依托四川茂县跃龙门铁路隧道工程,以主线单线隧道与横通道正交结构为研究对象,通过ABAQUS建立有限元分析模型。选取El-Centro地震波数据,通过应用扩展有限元理论,对横通道与主隧道交叉结构在最不利地震条件下的裂损进行研究,并提出减震层结合柔性接头的抗震措施。研究分析得到:减震层结合柔性接头的设置减小并抑制了交叉结构隧道在强震作用下的开裂范围。柔性接头的设置阻止了纵向裂缝的扩展,在交叉口处中部设置环向柔性接头能完全阻止交叉部位拱顶的裂缝生成;在初期支护和二次衬砌之间设置减震层,给予衬砌更大变形空间,使二次衬砌不易受初期支护变形受力影响而开裂。  相似文献   

西藏羌北高原多格错仁盐湖中更新世晚期以来的环境演化记录     

李金锁  刘喜方  牛新生  商斌  李国臣 《地质学报》2020,94(10):3130-3143

通过对西藏藏北高原多格错仁盐湖湖岸3101cm高度剖面进行地形地貌、地层沉积特征、矿物学特征及粒度、频率磁化率等气候环境变化指标的分析研究发现，整个剖面反映出大致6个较大的气候变化过程：233. 3kaBP～223. 5kaBP气候波动较大，总体趋势气候趋于干冷，期间出现过两次较温暖气候，之后气候逐渐变冷；在223. 5kaBP～213. 6kaBP总体变化为气温大幅度上升，但在期间有一次较大的相对冷干过程；213. 6kaBP～170kaBP之间总体变化气候趋于变冷，中间有2次明显的气候变暖湿过程及两次冷干过程；170kaBP～117. 1kaBP气候转为明显湿热；117. 1kaBP～75. 6kaBP气候变化趋势明显降低；75. 6kaBP～56. 7kaBP气候又明显上升达到湿热状态。以上气候波动规律与极地冰芯记录及深海氧同位素记录的古气候波动规律有很好的一致性，同时本盐湖区与柴达木盆地察尔汗盐湖区的CH0310钻孔及青海湖南岸二郎剑阶地的 QH 86钻孔所揭示的中更新世晚期以来的气候变化的分析对比，发现西藏羌北的多格错仁盐湖区与青海的察尔汗盐湖区及青海湖湖区在更新世中晚期以来的气候环境变迁存在极好的可比性，说明青藏高原的气候演化在中晚更新世以来基本具有一致性，在时间上的微小超前与滞后具有区域上的细微变化，说明气候变迁在不同的区域又具有各自的独特性。  相似文献   

水源钻机在超深土层绳索取心钻进中的应用          下载免费PDF全文

杨联锋  段云星 《探矿工程》2020,47(11):44-50

山西省清徐县区域地质调查项目设计800、2000、3000 m科学钻探孔，以调查填补新生界底板埋深控制空白区，各孔钻入基岩30 m完钻。要求全孔取心，岩心采取率≮85%，岩心直径≮60 mm，采用塑料保护管采取原状岩样。针对超深软土层、各组地层特性及厚度未知、钻遇基岩完钻深度未知、大直径高保真全孔取心、项目价格远低于目前市场成本等难题，经过“水源钻机+大提钻取心+长裸眼孔段”实施800 m孔、“岩心钻机+绳索取心+套管固井”实施640 m参数对比孔，创新性使用“水源钻机+绳索取心+长裸眼孔段”工艺完成了2000 m孔的施工。该工艺岩心采取率达到93%，孔径和孔斜符合地质要求，为3000 m孔顺利施工打下了坚实的基础，为同类型项目提供了经验和借鉴。  相似文献   

Radar isochronic layer dating for a deep ice core at Kunlun Station,Antarctica     

Tang  Xueyuan  Sun  Bo  Wang  Tiantian 《中国科学:地球科学(英文版)》2020,63(2):303-308

The ages and accumulation rates of ice are important boundary conditions for paleoclimatic ice models. Radardetected isochronic layers can be used to date the ice column beneath the ice surface and infer past accumulation rates. A Deep Ice-Core Drilling Project has been carried out at Kunlun station in the Dome A region, East Antarctica. Radio echo sounding data are collected during the 2004/2005 Chinese National Research Expedition and the 2007/2008 Dome Connection East Antarctica project of the Alfred Wegener Institute(Germany). Radar isochronic layers from the dataset were linked to compare a new deep ice core site from Kunlun station and the Vostok ice core site. Ten visible layers, accounting for ~50% ice thickness at the Kunlun station ice core site, were dated based on the Vostok ice core chronology. At 1,640 m depth below surface, an age of ~160,400 yr was determined, corresponding to a bright layer at Kunlun station. These layers provided geometric information on the past surface of the ice sheet around the ice core site through the Wisconsin glacial stage, Eemian interglacial and Marine Isotope Stage6. Based on a simple ice flow model and the age-depth relationship, we concluded that the region around the Kunlun ice core site had lower past accumulation rates, consistent with the present pattern. The age-depth relationship would thus be expected to correlate and constrain the chronology of the deep ice core at Kunlun station in the future.  相似文献   

Wedge impact with the influence of ice     

《Applied Ocean Research》2019

This work presents a canonical study on a wedge entering water near a single piece of ice using computational-fluid-dynamics (CFD) and a Wagner-type theoretical model with corrections for non-linear effects. Calculations for a series of conditions with ice of different sizes and locations relative to the wedge are conducted. The hydrodynamic force due to impact, the pressure distribution on the wedge surface, and the pile-up phenomenon are examined to study the role of ice in the impact process. The theoretical model is shown to be accurate and can serve as a useful method to assess slamming loads under the influence of ice. It is shown that even for the case of a small piece of ice, the slamming force on the wedge can increase by 30%.  相似文献   

沉积物中硬质粘土层的研究进展          下载免费PDF全文

孔凡彪  徐树建  贾广菊 《山东国土资源》2018,34(3)

大量的钻孔资料表明,平原地区及其海域沉积物中普遍有硬质粘土层的存在。硬质粘土层在工程地质、地理学研究等方面具有重要的价值,它不仅是高层建筑的持力层,而且是研究全球环境变化事件、古气候演变的良好载体。该文阐述了硬质粘土层的一般特征、成因以及在粒度、地球化学元素、年代学、沉积环境等方面的研究进展,并展望了硬质粘土层在年代、物质来源和沉积环境等方面的研究方向,认为黄河三角洲硬质粘土层研究较少,需要开展大范围的、系统深入的、多学科的宏观和微观综合分析,挖掘硬质粘土层蕴含的古环境意义和应用价值。  相似文献   

北太平洋副热带模态水盐度的年代际变化     

胡睿坤  边志刚  刘子洲  刘聪  翟方国  顾艳镇 《中国海洋大学学报(自然科学版)》2020,(2):9-21

副热带模态水(Subtropical Mode Water;STMW)在气候变化中起着重要作用。本文利用全球高分辨率数值模拟结果,研究了北太平洋STMW核心层盐度(Core Layer Salinity;CLS)的年代际变化及其物理机制。结果表明,CLS存在显著的年代际变化,其空间分布则与背景流场分布特征有关。侵蚀区CLS滞后生成区CLS约1~2年,这主要是海流平流输运引起的。生成区内,STMW的季节循环一般可分为生成期(12-4月)、隔离期(5-6月)和侵蚀期(7-11月),生成期混合层盐度(Mixed Layer Salinity;MLS)决定着隔离期和侵蚀期的CLS,而MLS年代际变化则主要由同太平洋年代际涛动存在负相关性的海表面淡水通量的变化引起。  相似文献   

关于土层地震反应分析中阻尼矩阵建模方式的讨论          下载免费PDF全文

殷琳  楼梦麟  康帅 《世界地震工程》2019,35(2):132-140

阻尼矩阵的选择对土层时域内地震反应计算的准确性有重要意义。本文构造了质量比例阻尼、刚度比例阻尼、Rayleigh阻尼、Caughey阻尼和Clough阻尼矩阵，研究各阻尼对土层地震反应分析精度的影响。以苏通大桥5号桥塔基础处的工程场地为例，分别以人工合成基岩波，Northridge波、Parkfield波和汶川波为输入，得到不同阻尼模型下土层的地震反应，结果表明Clough阻尼在计算精度和误差稳定性上要优于其他阻尼模型，针对Clough阻尼的不足之处提出了改进方法，算例表明改进后的Clough阻尼能在保证计算精度的前提下减少计算机的存储量和计算量。  相似文献