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991.
Meng WEI Qi SHU Zhenya SONG Yajuan SONG Xiaodan YANG Yongqing GUO Xinfang LI Fangli QIAO 《中国科学:地球科学(英文版)》2021,(6):853-865
The unexpected global warming slowdown during 1998–2013 challenges the existing scientific understanding of global temperature change mechanisms, and thus the simulation and prediction ability of state-of-the-art climate models since most models participating in phase 5 of the Coupled Model Intercomparison Project(CMIP5) cannot simulate it. Here, we examine whether the new-generation climate models in CMIP6 can reproduce the recent global warming slowdown, and further evaluate their capacities for simulating key-scale natural variabilities which are the most likely causes of the slowdown. The results show that although the CMIP6 models present some encouraging improvements when compared with CMIP5, most of them still fail to reproduce the warming slowdown. They considerably overestimate the warming rate observed in 1998–2013,exhibiting an obvious warming acceleration rather than the observed deceleration. This is probably associated with their deficiencies in simulating the distinct temperature change signals from the human-induced long-term warming trend and/or the three crucial natural variabilities at interannual, interdecadal, and multidecadal scales. In contrast, the 4 models that can successfully reproduce the slowdown show relatively high skills in simulating the long-term warming trend and the three keyscale natural variabilities. Our work may provide important insight for the simulation and prediction of near-term climate changes. 相似文献
992.
993.
行程时间不确定性导致了可达性随时间的变化,相关研究表明忽略行程时间不确定性会高估可达性水平。既有可达性研究往往用行程时间可靠性表示行程时间不确定性,但未考虑不同可达性模型结果的差异以及行程时间可靠性价值。本文结合各OD之间的行程时间分布特征,构建方差型的行程时间可靠性来描述行程时间不确定性,并进一步将行程时间可靠性纳入到广义出行时间成本中,建立了时间距离模型、潜力模型、累计机会模型和高斯模型4种基于位置的可达性测算方法,以比较在不同测算方法下,行程时间不确定性对可达性的影响。深圳的案例研究表明:(1)忽略行程时间不确定性会使全区域的可达性至少被高估5.04%,最大被高估95.04%。潜力模型、时间距离模型、累计机会模型和高斯模型的高估幅度由低到高;(2)行程时间不确定性对可达性的影响存在阈值效应,阈值越高,可达性受影响的程度越小;(3)从空间分布来看,行程时间不确定性对可达性水平高和低的区域都有一定影响。若不考虑行程时间不确定性,可达性高的区域高估值大,而在可达性低的区域,可达性高估的百分比较大,高估百分比中位数的差异程度最大可达77.1%;(4)行程时间不确定性对潜力模型可达性分类的... 相似文献
994.
Zhengchen LI Xianyan WANG Yang YU Huiping ZHANG Qi SU Xiaodong MIAO Huayu LU 《中国科学:地球科学(英文版)》2021,(6):906-919
Previous researches had emphasized tectonic impacts on the fluvial system at the tectonically active areas, while the effects of lithology and local base level change have received relatively rare attention. Here we investigated fluvial landforms at different spatial scales, focusing on knickpoints and channel network reorganization from an area affected by the Haiyuan Fault in the northeastern Tibetan Plateau. The geomorphic indices, i.e., drainage pattern and χ anomalies, were calculated and investigated. The results show that two regional radial drainages formed around the Laohu and Hasi Mountains. Within the interior of the radial drainage, tributaries from the southeast side of the Laohu Mountain experienced near 180° direction change.We interpret this as the gradual drainage capture originating from the height difference(~190 m) of the local base level between the two catchments. Some tributaries from the Hasi Mountain show alternating gorges and broad valleys controlled by lithology.Besides, tectonic uplift and the lowering of base level(from the incision of the Yellow River) triggered an autogenic positivefeedback transition from parallel to dendritic drainage patterns. These observations suggest that base level change and lithology play a crucial role in landscape evolution, even in a tectonically active region. 相似文献
995.
目前,经"CLGIS煤田测井综合解释程序"处理的测井数据为DOS系统下dat文件格式,由此产生的测井成果图无法用于提交规范的煤田地质报告,为此需将其转换为Windows操作系统下通用图形文件格式,如dwg、dxf等图形文件.通过分析dat测井数据的存贮格式,利用VB语言,结合Activex编程技术、Access数据库以及Autocad等绘图软件功能,使数字测井成果数据得以利用,实现"测井曲线综合柱状图"、"煤层测井曲线定厚图"、"测井曲线对比图"等图件的自动绘制. 相似文献
996.
997.
Epithermal deposits in North Xinjiang, NW China 总被引:23,自引:0,他引:23
Y. J. Chen F. Pirajno G. Wu J. P. Qi X. L. Xiong 《International Journal of Earth Sciences》2012,101(4):889-917
The North Xinjiang region (NW China) is an important part of the Central Asia Orogenic Belt, situated at the junction of Siberia, Tarim and Kazakhstan plates. It is an area characterized by multiple stages of Phanerozoic continental growth, during which several porphyry and epithermal systems were formed. The relationship of these mineral systems to the geodynamic evolution of the region has not yet been well understood. In this paper, we list the main geological characteristics of 21 significant epithermal precious and base metal deposits in North Xinjiang, and classify them into high-sulfidation and low-sulfidation styles, with the latter being predominant. We have selected seven epithermal deposits representing different styles formed under different tectonic regimes and discuss their geology and geochemistry in some detail. The deposit-scale geology and geochemistry of epithermal systems in North Xinjiang are essentially similar to those in other parts of the world. All epithermal deposits in North Xinjiang are hosted in volcanic rocks with ages ranging from Devonian to Triassic, with the Early Carboniferous volcanic sequences being the most important, followed by the Permian and Triassic. The Devonian–Early Carboniferous host rocks belong to the calc-alkaline series that developed in pre-collisional arc-back-arc basin systems; whereas the Permian–Triassic host volcanic rocks of shoshonite series formed in post-subduction regimes. Available isotopic ages of these epithermal systems cluster in two periods: Early Carboniferous (>320?Ma) and Late Carboniferous–Triassic (320–220?Ma), reflecting two metallogenic episodes that occurred during subduction-related accretion and post-subduction collision regimes, respectively. Accordingly, three groups of epithermal deposits in North Xinjiang can be recognized as (1) pre-collisional deposits without or with negligible collisional-related modification, (2) deposits formed in collision regime and (3) ore systems strongly overprinted by fluid flow in post-subduction collision regime. 相似文献
998.
为配合中国水利部组织编制全国主要江河防洪规划工作,对与编制防洪规划有关的若干重大问题进行了研究。提出用20世纪发生过的大洪水淹没范围作为界定防洪区的基础;风险管理最重要的是规避风险和应对风险,而规避风险的核心是约束人类不合理的经济社会活动,降低洪水灾害造成的风险;当防洪区受到两种洪水风险威胁时,应当采用二维概率分布核查防洪区的标准;合理提高城市防洪标准,是城市防洪的首要任务;要协调城市防洪与城市建设的关系,充分发挥城市拦蓄雨洪的作用(如保留必要的水面率、雨水利用等),蓄排兼顾,而不宜过分强调城市排水;建议根据淹没水深、淹没历时和洪水频率组成的洪水风险度因子划分蓄滞洪区风险区,并结合蓄滞洪区自然地理条件比选安全建设模式。 相似文献
999.
1000.
综合大洋钻探计划311航次沉积物中自生碳酸盐岩碳、氧稳定同位素特征 总被引:1,自引:3,他引:1
为了探索水合物背景下沉积物中自生矿物响应,对采自综合大洋钻探计划(IODP)311航次沉积物中自生碳酸盐岩颗粒进行了矿物组成、形貌特征和碳、氧稳定同位素特征等研究。X光粉晶衍射(XRD)和扫描电镜(SEM)结果显示碳酸盐岩颗粒的主要矿物成分是铁白云石和方解石,呈多孔状结核和不规则状集合体产出。碳酸盐岩颗粒的碳稳定同位素δ13CPDB低至-41.50‰,证实其碳源源自甲烷,其成因与甲烷厌氧氧化过程有关,印证了研究区存在海底甲烷渗漏现象,是甲烷水合物赋存区重要的识别标志之一。碳酸盐岩颗粒的氧稳定同位素δ18OPDB总体上随着沉积物深度增加而减小,可能指示沉积物的背景温度由下而上(从早到晚)逐渐降低。研究结果提供了现代海洋天然气水合物背景下沉积物中自生碳酸盐岩的碳、氧稳定同位素记录,对于寻找我国海域天然气水合物资源,探索地史时期古海洋沉积物中类似的甲烷事件记录具有重要的理论和实践指导意义。 相似文献