Nonlinear and multifractal approaches of the geomagnetic field   总被引：2，自引：0，他引：2  

L. Hongre  P. Sailhac  M. Alexandrescu  J. Dubois 《Physics of the Earth and Planetary Interiors》1999,110(3-4):157-190

Recent nonlinear dynamics techniques have been developed to analyse chaotic time series data. We first summarize the procedure which gives an appropriate reconstruction of the unknown dynamics from scalar measurements in a pseudophase space. It permits, firstly, the representation of the trajectories of the dynamical system—they define an attractor when the system is dissipative—by preserving its topological properties. We then present the invariant measures and ergodic quantities such as the multifractal spectrum and Lyapunov exponents which can be estimated on the reconstructed attractor. The multifractal analysis provides us with a characterization of the scaling energy of the process whereas the Lyapunov exponent gives another statistical measure of the stability of the dynamics. The estimation of these quantities was tested on synthetic data. The nonlinear and multifractal analyses were finally applied to the hourly mean values of the magnetic field recorded at the Eskdalemuir (ESK) observatory over 79 years (692,520 data measurements for each component). The estimations of a 5-dimensional pseudo-phase space and a positive Lyapunov exponent confirm the possibility of low-dimensional deterministic chaos in the magnetic field observations at ESK observatory. The correlation between the solar activity (the Wolf number), the unstable nature of the magnetic field, and the singularity spectrum points out the forcing of the solar cycles on the dynamics of the magnetic field at ESK observatory.  相似文献   

河南省汛期降水的天气季节特征   总被引：1，自引：0，他引：1  

吴富山  王魁山  符长锋 《气象学报》1999,57(3):367-375

通过多年汛期逐日降水量场的ＥＯＦ分析,探讨了河南省汛期降水的天气季节特征。河南省主汛期出现在江淮梅汛之后,称暑汛较合适。暑汛期降水出现明显的南北与东西方向上的反相振荡;尤其是从小暑到大暑,季风雨带从沙河以南,北跃到黄河沿岸及其以北地区,是东亚季风重要的气候特征,表明梅雨结束后,中国东部的主要雨带不是一跃而至黄河以北,而是阶段性地逐次向北跳跃的。对暑汛降水气候的分析研究,有助于加深对东亚季风活动的认识  相似文献   

高温微风条件下太湖流域风场时空特征分析   总被引：3，自引：2，他引：1  

王成林  黄娟  钱新 《湖泊科学》2011,23(1):122-128

适宜太湖蓝藻水华大面积形成的诸多因素中,气象因素主要是高温、微风.据此对太湖周边17个常规气象观测站的7年报文资料进行筛选,选择的17个站点同时满足时间为14点、气温大于2590、风速小于等于4m/s的风场进行分析,研究发现太湖流域风场空间特征以东南风居多,而且不同风向的背景风场吹过水面后.在下风向湖面及湖岸附近都存在...  相似文献   

一次黄海爆发性气旋的观测分析和数值模拟研究     

王彬  孙雅文  陈胜舰  张薇  刘桂艳 《海洋通报》2023,(5)

本文利用再分析资料和WRFV3.9模式（Weather Research and Forecasting Model）对2020年7月22－24日发生在黄海海域的一次爆发性气旋进行了研究,并对其演变过程和发展机制进行了详细分析。该气旋22日12UTC在山东南部生成,入海后开始爆发性发展,最大加深率达到1.2 Bergeron,23日在黄海中部气压降至最低990 hPa左右,24日在韩国登陆。高空强辐散、低层的暖舌结构、水汽输送和下垫面热通量的变化增强了大气斜压性,使其迅速发展。使用WRF模式对气旋进行模拟,涡度的诊断分析表明,大气低层强斜压性主要通过涡度方程的散度项对气旋的发展起作用,对流项在涡度发展旺盛的时刻也有一定影响。海温的敏感性试验表明,海温变化对气旋移动路径和中心气压影响明显。  相似文献   

The use of 3D modeling for the prediction of the seismic demands on the gravity dams          下载免费PDF全文

M. Bybordiani  Y. Arıcı 《地震工程与结构动力学》2017,46(11):1769-1789

Seismic behavior of gravity dams has long been evaluated using a representative two‐dimensional (2D) system. Formulated for the gravity dams built in wide canyons, the assumption is nevertheless utilized extensively for almost all concrete dams due to the established procedures as well as the expected computational costs of a three‐dimensional model. However, a significant number of roller‐compacted concrete dams, characterized as such systems, do not conform to the basic assumptions of these methods by violating the conditions on canyon dimensions and joint‐spacing/details. Based on the premise that the 2D modeling assumption is overstretched for practical purposes in a variety of settings, the purpose of this study is to critically evaluate the use of 2D modeling for the prediction of the seismic demands on these systems. Using a rigorous soil–structure interaction approach, the difference between the two and three‐dimensional response for gravity dams was investigated first in the frequency domain for a range of canyon widths and foundation to dam moduli ratios. Then, the time domain differences between the crest displacements and the maximum principal stress were obtained using 70 different ground motions in order to show the possible bias introduced into the analysis results due to the modeling approach. The results of the study show that even for relatively wide canyons, the 2D analysis can lead to misleading predictions. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Seismic performance of buildings retrofitted with nonlinear viscous dampers and adjacent reaction towers     

《地震工程与结构动力学》2018,47(5):1329-1351

An effective strategy of seismic retrofitting consists of installing nonlinear viscous dampers between the existing building, with insufficient lateral resistance, and some auxiliary towers, specially designed and erected as reaction structures. This allows improving the seismic performance of the existing building without any major alteration to its structural and nonstructural elements, which makes this approach particularly appealing for buildings with heritage value. In this paper, the nonlinear governing equations of the coupled lateral‐torsional seismic motion are derived from first principles for the general case of a multistory building connected at various locations in plan and in elevation to an arbitrary number of multistory towers. This formulation is then used to assess the performance of the proposed retrofitting strategy for a real case study, namely, a 5‐story student hall of residence in the city of Messina, Italy. The results of extensive time‐history analyses highlight the key design considerations associated with the stiffness of the reaction towers and the mechanical parameters of the nonlinear viscous dampers, confirming the validity of this approach.  相似文献   

海河流域暴雨的气候特征与环流分型     

杨德江  马宁  尉英华 《水文》2017,37(1):83-91

选用海河流域1961~2012年132站逐日降水资料,通过趋势分析、M-K检验、EOF和REOF等方法分析了50余年海河流域暴雨的气候统计特征。利用NCEP/NCAR再分析资料和历史天气图资料,研究了海河流域14个典型强致灾暴雨过程的大气环流特征。结果表明:(1)海河流域夏季暴雨日站数和暴雨量的时空分布相近,暴雨日站数下降趋势较为显著;(2)海河流域夏季暴雨的空间分布可划分为3个分布型态:西南型、东北型和东南型;(3)海河流域暴雨在20世纪70年代末至80年代初存在一次突变现象;(4)海河流域强致灾暴雨过程可归纳为5类主要环流型,即高空低槽型、高空冷涡型、副高外围切变线型、低空低涡型和台风北上型。  相似文献   

1948—2005年7月500hPa高度场EOF分析     

古月 《内蒙古气象》2010,(1):4-6

利用1948—2005年逐年7月份的NCEP/NCAR格点资料,对北半球的亚洲和太平洋区域500hPa高度场进行经验正交函数(EOF)分解,分析了前3个特征向量(模态)的空间分布特征和时间系数的变化,结果表明:7月份的500hPa高度场的分布特征比较复杂,但第一模态有一定的代表性,反映出西太平洋副热带地区高度场与亚洲大陆的反相关关系,而这种关系在20世纪80年代以后出现了反位相的变化。  相似文献   

Dating of rockfall damage in trees yields insights into meteorological triggers of process activity in the French Alps     

R. Mainieri  C. Corona  J. Chartoire  N. Eckert  J. Lopez-Saez  M. Stoffel  F. Bourrier 《地球表面变化过程与地形》2020,45(10):2235-2250

Rockfall release is a rather unpredictable process. As a result, the occurrence of rockfall often threatens humans and (infra)structures. The assessment of potential drivers of rockfall activity therefore remains a major challenge, even if the relative influence of rainfall, snowmelt, or freeze–thaw cycles has long been identified in short-term monitoring projects. In the absence of longer-term assessments of rockfall triggers and possible changes thereof, our knowledge of rockfall dynamics remains still lacunary as a result of the persisting scarcity of exhaustive and precise rockfall databases. Over the last decades, several studies have employed growth disturbances (GDs) in tree-ring series to reconstruct rockfall activity. Paradoxically, these series were only rarely compared to meteorological records. In this study, we capitalize on the homogeneity of a centennial-old reforestation plot to develop two reconstructions – R1 including only growth suppressions, and R2 based on injuries – with limited biases related to decreasing sample size and changes in exposed diameters back in time. By doing so, our study also and quite clearly highlights the large potential that protection forests have in terms of yielding reliable, multidecadal rockfall reconstructions. From a methodological perspective, we find no synchronicity between R1 and R2, as well as an absence of meteorological controls on rockfall processes in R1. This observation pleads for a careful selection of GDs in future reconstructions. In terms of process dynamics, we demonstrate that summer intense rainfall events (>10 mm day⁻¹) are the main drivers for rockfall activity at our study site. Despite the stringency of our detection procedure, correlations between rockfall activity and meteorological variables remain comparable to those reported in previous studies, as a result of the complexity and multiplicity of triggering factors. We therefore call for a more systematic coupling of tree-ring analysis with rockfall and microclimatic monitoring in future studies. © 2020 John Wiley & Sons, Ltd.  相似文献   

Seismic reliability assessment and the nonergodicity in the modelling parameter uncertainties     

Fatemeh Jalayer  Hossein Ebrahimian 《地震工程与结构动力学》2020,49(5):434-457

Modelling uncertainty can significantly affect the structural seismic reliability assessment. However, the limit state excursion due to this type of uncertainty may not be described by a Poisson process as it lacks renewal properties with the occurrence of each earthquake event. Furthermore, considering uncertainties related to ground motion representation by employing recorded ground motions together with modelling uncertainties is not a trivial task. Robust fragility assessment, proposed previously by the authors, employs the structural response to recorded ground motion as data in order to update prescribed seismic fragility models. Robust fragility can be extremely efficient for considering also the structural modelling uncertainties by creating a dataset of one-to-one assignments of structural model realizations and as-recorded ground motions. This can reduce the computational effort by more than 1 order of magnitude. However, it should be kept in mind that the fragility concept itself is based on the underlying assumption of Poisson-type renewal. Using the concept of updated robust reliability, considering both the uncertainty in ground motion representation based on as-recorded ground motion and non ergodic modelling uncertainties, the error introduced through structural reliability assessment by using the robust fragility is quantified. It is shown through specific application to an existing RC frame that this error is quite small when the product of the time interval and the standard deviation of failure rate is small and is on the conservative side.  相似文献