大震前地磁场时空间线性度变化的初步研究     

陈化然  冯德益 《地震地磁观测与研究》1994,(5)

把用来分析地震波波形的时间线性度和空间线性度两种方法，应用到地磁资料分析当中，具体分析处理了１９７６年７月２８日唐山Ｍｓ７．８地震和１９８９年１０月１９日大同Ｍｓ６．１地震前后地磁场资料，并对这两次地震前后地磁时空线性度变化情况进行了研究。所得结果表明：①较大地震前地磁场的时空线性度均可能呈现出较明显的下降异常变化，有些在震前回升，②各分量的时空线性度呈现异常的时间基本上同步，并与波速异常发展趋势基本相符。  相似文献   

地震波动力学特征变化指标在短期地震预报中的应用   总被引：13，自引：2，他引：13  

冯德益  虞雪君 《地震》1994,(1):12-22

本文研究了地震前地震波动力学特征的变化，主要是波形和频谱的变化，并从中提取出可望在短期（半年以内）地震预报中应用的一些预报指标。这些指标包括：Ｐ波初始部分波形的时间线性度和空间线性度，初始段平均半周期，Ｓ，Ｐ波频谱的峰值频率，拐角频率，相对带宽度，相对频谱峰值，高频段的谱线斜率绝对值等。同时还研究了短周期地脉动的波形线性度及频谱特征量（峰值频率等）在大震前出现的短期（半年以内）和临震（９天以内）的  相似文献   

西北太平洋热带气旋路径时间标度律的研究     

肖天贵 《南京气象学院学报》1995,18(3):444-449

时间标度计算表明，西北太平洋热带气旋路径是一个无标度性的系统，其关联方差谱遵从频率的－２￣－３次方幂律，不同背景下的路径系统均如此。由此得到的不同季节、不同地域的热带气旋路径可预报时间尺度基本上为３￣４ｄ，但异常热带气旋路径的可预报时间尺度则为１￣２ｄ。  相似文献   

Further Studies Of Atmospheric Turbulence In Layers Near The Surface: Scaling The Tke Budget Above The Roughness Sublayer   总被引：2，自引：0，他引：2  

Paul Frenzen  Christoph A. Vogel 《Boundary-Layer Meteorology》2001,99(2):173-206

The second of two experimental studies of the TKE budget conducted on sites of different roughness is described, and results are compared. The first took place within a shallow layer above a small field of mostly bare, cultivated soil; the second was carried out above a roughness sublayer of significant depth on an extensive plain of tall dry grass. Budget terms observed in the second study were scaled with a modified u which compensated for effects of an unusually large stress gradient and ensured that the _m functions would be collinear. By showing that the modification becomes negligible in smaller gradients, it is demonstrated that in normal conditions, budgets observed above significant roughness sublayers should be normalized by scaling in terms of the unreduced Reynolds stress at the sublayer's upper surface. This procedure is shown to be consistent with the expectation that TKE budgets in layers near the surface all scale in fundamentally the same way.Other findings include: (1) the fact that most _m functions previously reported are not quite collinear is attributed to a type of overspeeding known to affect three-cup anemometers; (2) revised _m functions, collinear and largely free of the effects of overspeeding, are determined from a well-established characteristic of the linear _m relation for the stable case; (3) data that define collinear _m functions can also be represented with single hyperbolic curves; (4) dissipation is found to be 10 to 15% too small to balance total TKE production in unstable and neutral conditions and to decrease with increasing z/L in thestable regime; and (5) new relations for based on the observed behaviour of the dissipation deficit provide an improved closure for the set of equations that express the budget terms as functions of _m and z/L.  相似文献   

Gully‐head erosion processes on a semi‐arid valley floor in Kenya: a case study into temporal variation and sediment budgeting     

D. J. Oostwoud Wijdenes  R. Bryan 《地球表面变化过程与地形》2001,26(9):911-933

A three year monitoring programme of gully‐head retreat was established to assess the significance of sediment production in a drainage network that expanded rapidly by gully‐head erosion on the low‐angled alluvio‐lacustrine Njemps Flats in semi‐arid Baringo District, Kenya. This paper discusses the factors controlling the large observed spatial and temporal variation in gully‐head retreat rates, ranging from 0 to 15 m a^?1. The selected gullies differed in planform and in runoff‐contributing catchment area but soil material and land use were similar. The data were analysed at event and annual timescales. The results show that at annual timescale rainfall amount appears to be a good indicator of gully‐head retreat, while at storm‐event timescale rainfall distribution has to be taken into account. A model is proposed, including only rainfall (P) and the number of dry days (DD) between storms: which explains 56 per cent of the variation in retreat rate of the single‐headed gully of Lam1. A detailed sediment budget has been established for Lam1 and its runoff‐contributing area (RCA). By measuring sediment input from the RCA, the sediment output by channelized flow and linear retreat of the gully head for nine storms, it can be seen that erosion shifts between different components of the budget depending on the duration of the dry period (DD) between storms. Sediment input from the RCA was usually the largest component for the smaller storms. The erosion of the gully head occurred as a direct effect of runoff falling over the edge (GH_waterfall) and of the indirect destabilization of the adjacent walls by the waterfall erosion and by saturation (GH_mass/storage). The latter component (GH_mass/storage) was usually much larger that the former (GH_waterfall). The sediment output from the gully was strongly related to the runoff volume while the linear retreat, because of its complex behaviour, was not. Overall, the results show that the annual retreat is the optimal timescale to predict retreat patterns. More detailed knowledge about relevant processes and interactions is necessary if gully‐head erosion is to be included in event‐based soil erosion models. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

大气环流的季节突变与季风的建立II·个别年份南海夏季风的情况   总被引：1，自引：0，他引：1  

张铭  张东凌  左瑞亭  何卷雄  曾庆存 《气候与环境研究》2005,(3)

将流的标准化变差度概念应用到各年南海夏季风建立研究中去,并用其作为大气环流调整的客观定量指标。用该指标定义的南海夏季风建立的预兆日期与用传统天气气候学方法确定的南海夏季风的来临日期,在绝大多数具体年份两者均很接近,故可作南海夏季风建立的先兆指标。但有一些年份,南海季风的建立不伴随着低空环流的突变过程,两种方法都可能不准确,可靠的方法也许是用场相似度作指标。此外,南海夏季风建立前,对流层顶和平流层下层就出现了环流调整,该调整为南海夏季风建立打下基础,而南海夏季风爆发则表现为低空环流的大调整。南海夏季风的爆发是高、低空全球大气环流发生显著调整的结果,并非限于南海范围局部,南海夏季风建立不能看作是发生在南海的局部现象。  相似文献   

Theory and application for retrieval and fusion of spatial and temporal quantitative information from complex natural environment     

Jin Yaqiu 《Frontiers of Earth Science》2007,1(3):284-298

This paper briefly presents the research progress of the State Major Basic Research Project 2001CB309400, “Theory and Application for Retrieval and Fusion of Spatial and Temporal Quantitative Information from Complex Natural Environment”. Based on the rapid advancement of synthetic aperture radar (SAR) imagery technology, information theory of fully polarimetric scattering and applications in polarimetric SAR remote sensing are developed. To promote the modeling of passive microwave remote sensing, the vector (polarized) radiative transfer theory (VRT) of complex natural media such as inhomogeneous, multi-layered and 3-dimensional VRT is developed. With these theoretical progresses, data validation and retrieval algorithms for some typical events and characteristic parameters of earth terrain surfaces, atmosphere, and oceans from operational and experimental remote sensing satellites are studied. Employing remote sensing, radiative transfer simulation, geographic information systems (GIS), land hydrological process, and data assimilation, the Chinese land data assimilation system (CLDAS) is established. Towards the future development of China’s microwave meteorological satellites, employing remote sensing data of currently available SSM/I (special sensor microwave/imager), AMSU (advanced microwave sounding unit), MTI (microwave temperature imager), etc., with ground-based measurements, several operational algorithms and databases for atmospheric precipitation, water vapor and liquid water in clouds, and other hydrological/hydrological applications are developed. To advance China’s SAR and InSAR (interferometric SAR) technologies, the image processing and analysis of ERS (European remote sensing), Radarsat SAR, and Chinese SAR, etc., the software platforms are accomplished. Based on the researches of multi-information fusion, some simulations, identification, and information extractions of the targets from complex background clutter scenes are studied. Some experiments of radio wave propagation in anomalous atmospheric status are also carried out. Translated from Advances in Earth Science, 2007, 22(2): 111–125 [译自: 地球科学进展]  相似文献   

复合荒漠化及其时空变化研究——以新疆艾比湖地区为例     

李虎  王晓峰 《福建地理》2007,(3)

以新疆艾比湖地区为研究区,通过对现有荒漠化监测指标体系的归纳分析,界定了复合荒漠化概念.利用遥感影像数据提取研究区各类荒漠化的现状与动态变化信息.研究结果表明:单一主导因子荒漠化类型面积占荒漠化土地总面积的82.29%,复合荒漠化面积占17.71%.2002~2005年,艾比湖湖面面积缩小了322.5073 km2,相应的总体土地荒漠化面积增加了7.18%,复合荒漠化面积增加了133%.土地荒漠化的过程同时也发生了变化,风蚀、复合荒漠化增加而土地盐渍化减少,荒漠化程度加重,复合荒漠化类型增加并向其他土地类型扩展.  相似文献   

Suspended sediment load transport in the Mississippi River basin at St. Louis: temporal scaling and nonlinear determinism     

Bellie Sivakumar  Ji Chen 《地球表面变化过程与地形》2007,32(2):269-280

This study investigates the dynamic behavior of suspended sediment load transport at different temporal scales in the Mississippi River basin. Data corresponding to five successively doubled temporal scales (i.e. daily, two‐day, four‐day, eight‐day and 16‐day) from the St. Louis gaging station in Missouri are analyzed. The investigation is focused on identifying possible low‐dimensional deterministic behavior in the suspended sediment load transport dynamics, with an aim towards reduction in model complexity. The correlation dimension method is used to identify low‐dimensional determinism. The suspended sediment load dynamics are represented through phase‐space reconstruction, and the variability is estimated using the (proximity of) reconstructed vectors in the phase space. The results indicate the presence of low‐dimensional determinism in the suspended sediment load series at each of the five temporal scales, with the variables dominantly governing the dynamics in the order of three or four. These results not only suggest the appropriateness of relatively simpler models but also hint at possible scale invariance in the suspended sediment load transport dynamics. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

空间信息可视化的现状与趋势   总被引：10，自引：0，他引：10  

刘纪平  常燕卿等 《测绘学院学报》2002,19(3):207-210

对空间信息可视化的现状进行了较为细致的总结，分析了目前空间信息可视化存在的问题。在此基础上，讨论了空间信息可视化的完整概念，提出了空间信息可视化位置特征、交互性、多维性和可视化多样性的本质特征，概括了数据组织与调度、静态可视化、过程模拟与探索性分析等空间信息可视化基本过程。最后，提出未来空间信息可视化主要关键技术。  相似文献