东北冷涡对海河流域初夏降水异常的影响   总被引：1，自引：0，他引：1       下载免费PDF全文

何丽烨  马宁  郭军 《地球物理学报》2017,60(10):3745-3752

东北冷涡是东亚中高纬度地区的重要天气系统,其频繁活动可能导致显著的气候效应,不仅对东北局地,而且对海河流域地区初夏降水产生影响.本文利用海河流域34个地面气象台站逐日降水资料以及NCEP/NCAR再分析资料,对东北冷涡与海河流域初夏降水的关系进行研究,结果表明:初夏东北冷涡活动与海河流域降水存在显著的相关关系,对其空间分布亦有重要影响.当东北冷涡活动偏多(少)时,海河流域北部地区(尤其是海河下游)初夏降水可能偏多(少),对应时间系数为正(负)时海河流域初夏降水EOF第二模态北多(少)南少(多)的空间分布.在东北冷涡活动偏多年,东北冷涡引导北方"干冷"空气南下推进至海河流域北部,伴随该地区源自西风带水汽输送和水汽辐合的增强,形成了"上干下湿"的不稳定层结,在上升运动的触发下,导致海河流域北部初夏降水偏多;而东北冷涡活动偏少年情况正好相反.东北冷涡活动为海河流域尤其是海河下游地区初夏降水预测提供了具有参考意义的结果,其活动指数与海河下游初夏降水距平的符号一致率在近30年高达83%.  相似文献   

CHARACTERISTICS OF FOCAL MECHANISMS AND STRESS FIELD OF YUNNAN AREA          下载免费PDF全文

SUN Ye-jun  ZHAO Xiao-yan  HUANG Yun  YANG Hao  LI Feng 《地震地质》2017,39(2):390-407

Using the seismic waveform data recorded by regional seismic network of Yunnan and Sichuan and the method of CAP, we calculate and obtain the focal mechanism of 268 earthquakes with the magnitude of M_L≥4.0 occurring in Yunnan during Jan. 1999 to Aug. 2014; then, we analyze the types and the regional feature of the focal mechanism of earthquakes in Yunnan, on the basis of the focal mechanism of 109 earthquakes analyzed by Harvard University. Based on the data of the above focal mechanism solutions, we adopt the method of damped regional-scale stress inversion to calculate the best-fitting tectonic stress tensor of every grid in Yunnan; and adopt the method of maximum principal stress to calculate the direction of maximum horizontal principal stress in Yunnan. The result shows that: (1)the strike-slip type is the most principal type of the earthquake focus in the study area and the second is the normal faulting type; while, the reverse-fault type is relatively small. The spatial distribution of focal mechanism is obvious. This reflects that the dynamic source and acting force are different in different parts of the study area. (2)The direction of the stress field in Yunnan shows a certain spatial continuity. Maximum horizontal principal compressive stress is mainly clockwise from north to south and counterclockwise from the west to the east. The direction of stress field shows inhomogeneity in space. There exist two stress conversion zones respectively in EW and NS direction. The inversion result of stress field shows that the stress field in Yunnan is complex and the principal stress direction changes greatly; and there are obvious differences in different regions.  相似文献   

南北地震带北段的远震P波层析成像研究   总被引：5，自引：4，他引：1       下载免费PDF全文

郭慧丽  丁志峰  徐小明 《地球物理学报》2017,60(1):86-97

本文利用"中国地震科学台阵"探测项目在南北地震带北段布设的678个流动地震台站在2013年10月至2015年4月期间记录到的远震波形数据,经过波形互相关拾取到473个远震事件共130309条P波走时残差数据,通过远震层析成像研究获得了该区(30°N-44°N,96°E-110°E)下方0.5°×0.5°的P波速度扰动图像.结果显示,研究区下方P波速度结构显示强烈的不均一性和显著的分区、分块特征.岩石圈速度结构具有显著的东西差异:祁连、西秦岭和松潘甘孜地块组成的青藏东北缘地区显示明显的低速异常,而属于克拉通性质的鄂尔多斯地块和四川盆地则显示高速异常,表明东部克拉通块体对青藏高原物质的东向挤出起到了强烈的阻挡作用.阿拉善地块显示出弱高速和局部弱低速的异常并存的特征.阿拉善地块西部显示低速异常,而东部与鄂尔多斯相邻的地区显示高速异常,可能表明该地区的岩石圈的变形主要受到青藏高原东北缘的挤压作用.在鄂尔多斯和四川盆地之间的秦岭下方100~250 km深度上表现为明显的低速异常,表明该处可能存在软流圈物质的运移通道.鄂尔多斯北部的河套裂陷盆地下方在100~500 km深度内低速异常表现明显,说明该区有深部热物质上涌且至少来源于地幔过渡带.青藏东北缘上地幔显示低速异常且地幔过渡带中出现明显的高速异常,这种结构模式暗示了在青藏高原东北缘可能发生了岩石圈拆沉作用,而高速异常体可能是拆沉的岩石圈地幔.  相似文献   

基于解析信号重构的同步挤压小波变换的时频谱影响因素分析          下载免费PDF全文

游龙庭  宋建国  于会臻  王月蕾 《CT理论与应用研究》2017,26(3):267-278

受测不准原理的制约,小波变换、S变换等时频分析算法无法同时获得高时间分辨率和高频率分辨率。为了满足更高的要求,出现了一种联合小波变换和时频谱重组的新方法—同步挤压小波变换。本文从同步挤压小波变换和基于解析信号重构的同步挤压小波变换的原理出发,通过模型分析算法中参数设置对时频分析结果的影响,包括小波母函数、小波母函数的参数选择和小波阈值等,分析瞬时频率变化率不为零的信号所存在的时频谱模糊现象,并通过控制小波母函数、小波母函数参数以及小波阈值有效地减轻瞬时频率变化率不为零的信号所存在的时频谱模糊现象,时频谱的质量得到一定程度的提高。研究结果对获取高分辨率地震时频谱具有一定的指导意义。   相似文献   

Variation in reach‐scale thalweg‐migration intensity in a braided reach of the lower Yellow River in 1986–2015          下载免费PDF全文

Jie Li  Junqiang Xia  Meirong Zhou  Shanshan Deng  Xiaolei Zhang 《地球表面变化过程与地形》2017,42(13):1952-1962

Thalweg migration of an alluvial river plays a key role in channel evolution, which may influence the effect of existing river training works and biodiversity on floodplains, and cause losses in riparian land and property. The braided reach of the Lower Yellow River underwent continuous channel aggradation during the period from 1986 to 1999, and then remarkable channel degradation in 1999–2015 owing to the state of operation of the Xiaolangdi Reservoir in 1999. Here we quantify associated thalweg migration changes and identify the key influencing factor in the braided reach. Thalweg‐migration distances and intensities at section‐ and reach‐scales were calculated during the past 30 years from 1986 to 2015, in order to investigate the characteristics of thalweg migration in the reach. There was a 47% reduction in the reach‐scale thalweg‐migration distance and a 35% reduction in the corresponding migration intensity after the reservoir operation. It is also revealed that fluvial erosion intensity is a dominant factor in controlling the thalweg migration, based on the investigation into various influencing factors in the study reach. The thalweg‐migration intensity of the braided reach can be expressed as a power function of the previous four‐year average fluvial erosion intensity. The calculated thalweg‐migration intensities in 1986–2015 using the proposed relation generally agree with the observed data. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

利用GPS三频数据计算电离层垂直总电子含量变化率          下载免费PDF全文

管斌  孙中苗  刘晓刚  朱永兴 《地球物理学报》2017,60(3):887-896

研究了通过采样间隔为1 s的GPS三频载波相位观测数据计算1 Hz电离层垂直总电子含量变化率(RVTEC)的方法,推导了直接采用双频载波相位观测量计算RVTEC的公式,对一般空间环境与电离层活动剧烈两种条件下L1L2、L1L5、L2L5三种载波相位组合计算的RVTEC进行了一致性分析,给出了通过三频载波相位观测数据计算电离层RVTEC的修正方法,比较了X射线太阳耀斑期间RVTEC与由传统方法计算的总电子含量变化率(ROT)响应,在双星串飞编队测高模式下对计算方法进行了应用.结果表明,L1L2、L1L5两种组合之间的一致性较好,由L1L2、L1L5组合计算的RVTEC的中误差约为0.004 TECu/s,RVTEC较ROT更能体现TEC变化的细节,在双星串飞编队测高模式下海面高梯度的计算中,电离层延迟之差可以忽略.  相似文献   

A high‐resolution multi‐proxy lake record of Holocene environmental change in southern Iceland          下载免费PDF全文

CELENE L. BLAIR  ÁSLAUG GEIRSDÓTTIR  GIFFORD H. MILLER 《第四纪科学杂志》2015,30(3):281-292

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Assessing the ‘two water worlds’ hypothesis and water sources for native and exotic evergreen species in south‐central Chile          下载免费PDF全文

P. Hervé‐Fernández  C. Oyarzún  C. Brumbt  D. Huygens  S. Bodé  N. E. C. Verhoest  P. Boeckx 《水文研究》2016,30(23):4227-4241

Recent studies using water‐stable isotopes (δ¹⁸O and δ²H) have suggested an ecohydrological separation of water flowing to streams or recharging groundwater and water used by trees, known as the ‘two water worlds’ (TWW) hypothesis. In this study, we measured water isotopic composition in precipitation [open field and throughfall, i.e. local meteoric water line (LMWL)] and the mobile water compartment (i.e. stream and soil solution), bulk soil water and xylem water over a period of 1.5 years in two headwater catchments: NF, covered with old growth native evergreen forest (Aetoxicon punctatum, Laureliopsis philippiana and Eucriphya cordifolia), and EP, covered with 4 and 16‐year‐old Eucalyptus nitens stands. Our results show that precipitation, stream and soil solution plot approximately along the LMWL, while xylem waters from all studied tree species plot below the LMWL, supporting the TWW hypothesis. However, we also found evidence of ecohydrological connectivity during the wet season, likely controlled by the amount of antecedent precipitation. These observations hold for all investigated tree species. On both sites, a different precipitation source for stream and xylem water was observed. However, in EP, bulk soil showed a similar precipitation source as xylem water from both E. nitens stands. This suggests that E. nitens may use water that is recharging the bulk soil compartment. We conclude that under a rainy temperate climate, the TWW hypothesis is temporal and does not apply during wet seasons. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

One‐dimensional dynamics of saturated incompressible porous media: analytical solutions and influence of inertia terms          下载免费PDF全文

Yunpeng Zhang  Dorival M. Pedroso  Wolfgang Ehlers 《国际地质力学数值与分析法杂志》2016,40(18):2489-2513

The complexity of formulations for the hydromechanical coupled mechanics of porous media is typically minimised by simplifying assumptions such as neglecting the effect of inertia terms. For example, three formulations commonly employed to model practical problems are classified as fully dynamic, simplified dynamic and quasi‐static. Thus, depending on the porous media conditions, each formulation will have advantages and limitations. This paper presents a comprehensive analysis of these limitations when solving one‐dimensional fully saturated porous media problems in addition to a new solution that considers a more general loading situation. A phase diagram is developed to assist on the selection of which formulation is more appropriate and convenient regarding particular cases of porosity and hydraulic conductivity values. Non‐dimensional formulations are proposed to achieve this goal. Results using the analytical solutions are compared against numerical values obtained with the finite element method, and the effect of porosity is investigated. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

RN-FD型固体氡气源的稳定性及应用分析     

李朝明  杨志坚  褚金学  吴谋 《震灾防御技术》2018,13(1):114-124

对测氡仪器进行精确校准是氡测量工作中的重要环节，固体氡气源的稳定性、可靠性在校准中则显得至关重要。本文通过分析RN-FD型固体氡气源对闪烁室K值的稳定性实验结果，认为:RN-FD型固体氡气源标称的浓度值与实际浓度值不一致，标称浓度值只是理论浓度值而不是实际浓度值，需重新刻度才能使用；RN-FD型固体氡气源抽气循环时间不同则浓度不同，但抽气循环时间固定，观测结果比较稳定；对于没有α检查源的台站，RN-FD型固体氡气源可用于氡观测仪器坪区检查。  相似文献