2016与1998年春季北大西洋海表温度异常的差异及成因     

薛文璟  余锦华  陈林 《热带海洋学报》2020,39(3):19-30

利用再分析资料以及混合层海温诊断方程, 研究1997—1998与2015—2016年超级厄尔尼诺次年北大西洋海表温度异常(sea surface temperature anomalies, SSTA)的差异及成因。结果显示, 北大西洋SSTA在1998年春季呈明显正负正三极型式分布, 而在2016年呈弱的负正负型态。诊断热带北大西洋SSTA的影响因素表明, 1998年春季暖SSTA除了之前研究强调的海洋表面向大气的潜热输送异常减少, 以及吸收太阳辐射的增加外, 海洋动力过程即Ekman纬向漂流也起着重要的作用。热力过程与厄尔尼诺峰值后出现的北大西洋涛动(North Atlantic Oscillation, NAO)负位相有关, 其可引起亚速尔高压减弱, 产生西南风异常, 通过风-蒸发-海表温度(sea surface temperature, SST)反馈机制使热带北大西洋蒸发减弱, 海表增暖, 沃克环流下沉支的东移对这一增暖也有贡献。与1997—1998厄尔尼诺事件不同, 2015—2016厄尔尼诺事件没有强迫出负位相NAO, 而是出现弱NAO正位相, 热带北大西洋为弱的东风异常, 使海表发生一定的冷却, 形成2016春季北大西洋SSTA与1998年的明显差异。  相似文献   

Intra-survey reservoir fluctuations – implications for quantitative 4D seismic analysis     

Veronica Omofoma  Colin MacBeth  Hamed Amini 《Geophysical Prospecting》2019,67(2):282-297

During the time taken for seismic data to be acquired, reservoir pressure may fluctuate as a consequence of field production and operational procedures and fluid fronts may move significantly. These variations prevent accurate quantitative measurement of the reservoir change using 4D seismic data. Modelling studies on the Norne field simulation model using acquisition data from ocean-bottom seismometer and towed streamer systems indicate that the pre-stack intra-survey reservoir fluctuations are important and cannot be neglected. Similarly, the time-lapse seismic image in the post-stack domain does not represent a difference between two states of the reservoir at a unique base and monitor time, but is a mixed version of reality that depends on the sequence and timing of seismic shooting. The outcome is a lack of accuracy in the measurement of reservoir changes using the resulting processed and stacked 4D seismic data. Even for perfect spatial repeatability between surveys, a spatially variant noise floor is still anticipated to remain. For our particular North Sea acquisition data, we find that towed streamer data are more affected than the ocean-bottom seismometer data. We think that this may be typical for towed streamers due to their restricted aperture compared to ocean-bottom seismometer acquisitions, even for a favourable time sequence of shooting and spatial repeatability. Importantly, the pressure signals on the near and far offset stacks commonly used in quantitative 4D seismic inversion are found to be inconsistent due to the acquisition timestamp. Saturation changes at the boundaries of fluid fronts appear to show a similar inconsistency across sub-stacks. We recommend that 4D data are shot in a consistent manner to optimize aerial time coverage, and that additionally, the timestamp of the acquisition should be used to optimize pre-stack quantitative reservoir analysis.  相似文献   

元谋地电场观测数据小波阈值去噪     

朱杰 《地震地磁观测与研究》2019,40(5):70-78

为了解决元谋地电场观测数据的噪声干扰问题,采用小波阈值去噪的方法,根据元谋地电场观测数据特征,选取适当的阈值及不同的小波函数、分解层数进行研究。综合各小波函数去噪效果,通过对相对误差、均方根误差、信噪比等指标进行评价,确定适合元谋地电场观测数据去噪的阈值为软阈值函数、分层阈值;最优小波函数分别为Sym4、Sym5、db6和db8;分解层数分别为5、7、9。最后应用研究结果处理实际地电场观测数据,取得了较好的去噪效果。  相似文献   

不同密度团头鲂(Megalobrama amblycephala)对轮叶黑藻(Hydrilla verticillata)和密刺苦草(Vallisneria denseserrulata)群落结构的影响     

王倩红  刘正文  甄伟  张秀梅  郝征  莫家勇  赵雪枫 《湖泊科学》2019,31(3):862-868

冠层型水草轮叶黑藻在富营养情况下，生长迅速，覆盖水面，对于草甸型水草密刺苦草具有明显的竞争优势.为控制轮叶黑藻的竞争优势，于湖北省鄂州市团头鲂原种场的一个池塘进行了原位围隔（10 m×10 m）实验，研究不同密度（0、0.5和1尾/m²）团头鲂牧食作用对轮叶黑藻和密刺苦草群落结构的影响，并通过无人机数字图像处理获取水草覆盖度信息.实验过程中，沉水植物总覆盖度未发生变化.研究发现，团头鲂选择性牧食使得密刺苦草生物量和覆盖度显著增加.随着牧食强度的加大，团头鲂对轮叶黑藻的控制效果显著，放养密度为1尾/m²的围隔中轮叶黑藻比例降幅最明显.群落中轮叶黑藻与密刺苦草的生物量之比迅速下降，由6.14减少至0.002，覆盖度之比由4.88左右减少至约1.44.图像处理结果与实际采样情况相吻合，且通过误差矩阵得到图像分类平均精度达到90%以上，表明无人机数字图像处理在一定条件下可以作为获取沉水植物覆盖度的一种有效辅助手段.实验结束后，1尾/m²组的围隔中密刺苦草成为优势种，其植株密度、株高、株重和单株叶片数均显著增加，草甸更加密实.实验结果表明，放养1尾/m²密度的团头鲂可以有效控制轮叶黑藻并维持密刺苦草种群优势，结果为团头鲂对湖泊沉水植物群落的控制提供了参考.  相似文献   

基于经验模态分解和小波分解估算海气通量涡相关计算中的截断时间尺度     

姜浩  赵中阔  樊伟  宋金宝 《海洋与湖沼》2018,49(6):1138-1150

基于时长38天的海表风场实测数据,应用经验模态分解(EmpiricalModeDecomposition,EMD)和小波分解(Wavelet Decomposition, WD)这两种数据处理方法首先对涡相关法中的截断时间尺度(CutoffTimescale,CTS)进行估算,结果显示:基于EMD与WD方法估算出的CTS一般都在40秒左右(EMD的结果略小),远远小于传统涡相关法中CTS的取值(固定为10分钟),且EMD和WD的使用使得每一段数据都能够根据自身的湍流特点而获得合适的CTS; EMD方法和WD方法有效的去除了计算结果中的非湍部分,且对通量传输方向的刻画也更加合理,极大提高了通量的计算精度,所得通量与传统方法计算的通量偏差平均值高达45%;研究还对EMD和WD的优缺点进行了对比分析,结果表明EMD相比于WD有更高的自主性,而WD对信号的分离程度则更高。  相似文献   

DEEP STRUCTURE OF NORTHERN HENAN PROVINCE AND ADJACENT AREAS DERIVED FROM GRAVITY AND SEISMIC SOUNDING DATA IN RELATION TO DISTRIBUTION OF EARTHQUAKES     

JIANG Lei  XU Zhi-ping  FANG Sheng-ming  YANG Li-pu  LI Yi-qing  XU Shun-qiang 《地震地质》2018,40(2):323-336

We conduct the wave field separation of the gravity field for northern Henan Province and adjacent areas by the wavelet multi-scale decomposition method, and obtain multi-order gravity wavelet details and regional gravity field information. Then the Parker density surface inversion is used to invert the Moho interface. Based on the analysis of wavelet details in different orders and results of three seismic sounding profiles available in this area, we attempt to reveal the deep crustal structure of the study area. Research results show that the crustal structure is dominated by uneven density distribution accompanied by uplifts and depressions in the region with obvious heterogeneities of the density in horizontal and vertical directions. The gravity field characteristics in the middle-upper crust correspond to the surface topography, the lower crust is dominated by the large-scale high-low gravity anomalies, and several major depression basins show the characteristics of low velocity and low density. At the same time, the depth of the Moho interface changes greatly, which forms the block structure pattern of the regional crustal thickness. Among these features, the area with relatively large variations of the Moho is located in the transition zone of the basin to the Taihang Mountains, or exactly the Moho mutation belt. The Moho interface of the basin area as a whole is dominated by the uplift intertwined with local variations, of which the least and largest depths are 31km and 37km, respectively. Due to the gravity isostasy, the crustal thickness is larger(about 41km)in the northwest of the Taihang Mountains, with less average crustal density. In the study area, earthquakes tend to occur around the transition zone with density changes where the Moho is locally convex. The seismogenic mechanism may be associated with upwelling of upper mantle materials, low-velocity and low-density structures in the middle-lower crust and connection of deep large faults. Moreover, the deep large faults play a controlling role in the distribution of regional earthquakes.  相似文献   

黔北正安地区五峰组—龙马溪组页岩气地质特征及有利区预测     

贺永忠  向坤鹏  安亚运  易成兴  杨忠琴  于宁 《中国地质调查》2020,7(3):21-29

为明确黔北正安地区上奥陶统五峰组至下志留统龙马溪组的页岩气地质特征,充分应用页岩气地质调查、重磁电、二维地震、地质调查井及测试分析等工作方法,开展黔北正安地区1:5万页岩气基础地质调查,对五峰组至龙马溪组富有机质页岩的分布、沉积环境、有机地球化学、岩石矿物、储集性能及含气性等特征进行分析研究,结果表明: 研究区五峰组—龙马溪组富有机质页岩为深水陆棚相沉积,主要分布有安场向斜、斑竹向斜和泥高向斜,厚度14.5~55 m,埋深0~3 200 m; 有机碳(TOC)含量1.0%~4.0%,有机质镜质体反射率(R_o)为1.82%~2.23%,有机质类型以Ⅰ型干酪根为主; 岩石主要由石英、长石和黏土矿物组成,脆性矿物含量高,一般大于50%; 孔隙度为2.03%~3.89%,渗透率为0.35×10^-5~1.86×10^-5μm²,表现为低孔、特低渗的特征; 最高含气量为2.88 m³/t,显示出较好的含气性特征。综合分析和评价圈出3个页岩气聚集有利区,分别为安场区块、斑竹区块和泥高区块,这为研究区页岩气进一步勘探开发指明了方向。  相似文献   

Re-examining urban region and inferring regional function based on spatial–temporal interaction     

Haiyan Tao  Keli Wang  Xuliang Li 《International Journal of Digital Earth》2019,12(3):293-310

Urban system is shaped by the interactions between different regions and regions planned by the government, then reshaped by human activities and residents’ needs. Understanding the changes of regional structure and dynamics of city function based on the residents’ movement demand are important to evaluate and adjust the planning and management of urban services and internal structures. This paper constructed a probabilistic factor model on the basis of probabilistic latent semantic analysis and tensor decomposition, for purpose of understanding the higher order interactive population mobility and its impact on urban structure changes. First, a four-dimensional tensor of time (T)?×?week (W)?×?origin (O)?×?destination (D) was constructed to identify the day-to-day activities in three time modes and weekly regularity of weekday/weekend pattern. Then we reclassified the urban regions based on the space clustering formed by the space factor matrix and core tensor. Finally, we further analysed the space–time interaction on different time scales to deduce the actual function and connection strength of each region. Our research shows that the application of individual-based spatial–temporal data in human mobility and space–time interaction study can help to analyse urban spatial structure and understand the actual regional function from a new perspective.  相似文献   

Inter- and intra-annual trend analysis of water level and flow in the middle and lower reaches of the Ganjiang River,China     

Di Zhu  Yue Ben  Xinfa Xu 《水文科学杂志》2020,65(12):2128-2141

ABSTRACT

The Ganjiang River is the largest tributary of Poyang Lake in China, and its hydrological regime variation greatly affects the utilization of regional water resources and the ecological environment of the lake. In this study, a novel trend analysis method, the Moving Average over Shifting Horizon (MASH), was applied to investigate the inter- and intra-annual trends of flow and water level from 1976 to 2016 at the Xiajiang and the Waizhou hydrological stations in the Ganjiang River. The Significant Change Rate Method (SCRM) was proposed to determine the MASH averaging parameters. The trend analysis results show a statistically significant decrease in water level series throughout the year and the relationship of flow and water level have changed greatly at the Waizhou station. The sediment load reduction, large-scale sand mining and water level decrease of Poyang Lake are identified as the main causes for the water level decrease.  相似文献   

无人机大比例尺测图像控点布设方案设计     

袁德宝  张新新  周振青  任兴达 《北京测绘》2020,(4):523-527

随着无人机技术的快速发展,无人机航空摄影测量的精度也大大改善,以无人机为平台低空摄影测量大比例尺地图成为可能。本文以旋翼无人机搭载非测量型相机,通过布设不同数量像控点进行分析和研究,得到无人机摄影测量在农村地区像控点布设规律。结果证明在合理像控点布设的情况下,无人机测图数字成果空中三角测量、平面和高程精度均可满足1∶500、1∶1000、1∶2000大比例尺地形测图的精度要求。  相似文献