共查询到20条相似文献，搜索用时 78 毫秒
1.
Geomagnetic Hazards to Conducting Networks 总被引：1，自引：0，他引：1
D. H. Boteler 《Natural Hazards》2003,28(2-3):537-561
Geomagnetic disturbances can disrupt the operation of conductingnetworks, such as power systems, pipelines and communication cables. In power systems,geomagnetically induced currents (GIC) flow to ground through power transformers,disrupting their operation and causing transformer heating, increased reactive power demand,and generating harmonics that can cause relay misoperation. In extreme cases these effectscan lead to power blackouts such as occurred on the Hydro-Québec system during a geomagneticstorm in March 1989 leaving 6 million people without power for 9 hours.Geomagnetic disturbances are the result of eruptions on theSun that send high energy particles streaming out into space. When these particles reach theEarth they interact with the magnetic field, generating currents that flow down into the ionosphere.The most intense currents are associated with the aurora and occur in an east-west bandacross Canada. It is the magnetic field produced by these ionospheric currents that is seen on theground as a magnetic disturbance.Prevention of geomagnetic effects on power systems hasfocussed on blocking the flow of GIC in the system. However, such measures are expensive andmany utilities rely on forecasts of geomagnetic activity to help them operate during disturbances.The Canadian Geomagnetic Forecast Service, operated by Natural Resources Canada,has been in operation since 1974 and now provides long term and short term forecasts for threelatitude regions of Canada.Research is needed on all aspects of the problem; from newinformation about solar eruptions for improving forecasting services; to understanding systemresponse to disturbances. Research on geomagnetic disturbances is conducted by the CanadianGeomagnetic Forecasting Centre and a number of active groups at Canadian universities; whileresearch on geomagnetic effects is conducted by affected industries, often in collaborationwith the forecasting centre. 相似文献
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The planet Mars lacks, today, a planetary, dynamic magnetic field, but strong, intense, localized magnetic fields of lithospheric origin, one to two orders of magnitude larger than the terrestrial lithospheric field, are present. This lithospheric magnetic field is the result of magnetization processes in the presence of a magnetic dynamo and of demagnetization processes after the dynamo shutdown, such as impact or volcanoes. This crude scenario can be more accurately specified by interpreting global and local models of the current magnetic field of Mars. Some specific areas are studied, including the intensely magnetized Terra Sirenum, as well as the magnetic anomaly associated with Apollinaris Patera. Magnetic minerals could be of primary and/or secondary origin; this latter would imply an early hydration of a basaltic crust. A scenario, in which Mars experienced a major polar wander due to the Tharsis bulge, prior to the cessation of its dynamo, is proposed and discussed. 相似文献
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用变差函数研究重磁场的区域变化特征.变差函数的变程反映重磁场的相干范围, 块金效应反映随机干扰, 基台值反映变异程度.重磁场的理论模拟说明: 重力场的相干范围大于磁场, 重磁场变程主要取决于场源深度, 浅源重磁场变差函数近似为球状模型或指数模型, 深源重磁场近似为连续性更好的高斯模型.磁场场源深度近似等于变程的一半, 重力场场源深度近似等于变程的四分之一.湖北大冶铁矿垂直分量磁异常具有几何各向异性, 北西-南东走向, 变差函数推测磁铁矿平均深度为250m.磁异常小波多尺度分解细节和逼近部分磁场具有协调几何各向异性, 变差函数的各阶场源深度估计结果与功率谱估计结果吻合. 相似文献
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We consider models of a wormhole (i) maintained by an electromagnetic field, taking into account quantum vacuum corrections to the equation of state, (ii) maintained by a combination of the magnetic field and phantom energy, with a spherically symmetrical equation of state, and (iii) with a magnetic field and phantom matter with an anisotropic equation of state. It is shown that the quantum corrections and the density and exoticity of phantom energy or matter can be as small as is desired. For an external observer, the entrance to the tunnel appears to be a magnetic monopole of macroscopic size. The accretion of ordinary matter onto the entrance to the tunnel may result in the formation of a black hole with a radial magnetic field. We consider the possibility that some active galactic nuclei and Galactic objects may be current or former entrances to magnetic wormholes. We consider the possible existence of a broad mass spectrum for wormholes, from several billion solar masses to masses of the order of 2 kg. The Hawking effect (evaporation) does not operate in such objects due to the absence of a horizon, making it possible for them to be retained over cosmological time intervals, even if their masses are smaller than 1015 g. We also discuss a model for a binary system formed by the entrances of tunnels with magnetic fields, which could be sources of nonthermal radiation and γ-ray bursts. 相似文献
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V. A. Sheminova 《Astronomy Reports》2009,53(5):477-486
Two-dimensional simulations of time-dependent solar magnetogranulation are used to analyze the horizontal magnetic fields and the response of the synthesized Stokes profiles of the IR FeI λ1564.85 nm line to the magnetic fields. The 1.5-h series of MHD models used for the analyses reproduces a region of the magnetic network in the photosphere with an unsigned magnetic flux density of 192 G at the solar surface. According to the magnetic-field distribution obtained, the most probable absolute strength of the horizontal magnetic field at an optical depth of τ 5 = 1(τ 5 denotes τ at λ = 500 nm) is 50 G, while the mean value is 244 G. On average, the horizontal magnetic fields are stronger than the vertical fields to heights of about 400 km in the photosphere due to their higher density and the larger area they occupy. The maximum factor by which the horizontal fields are greater is 1.5. Strong horizontal magnetic flux tubes emerge at the surface as spots with field strengths of more than 500 G. These are smaller than granules in size, and have lifetimes of 3–6 min. They form in the photosphere due to the expulsion of magnetic fields by convective flows coming from deep subphotospheric layers. The data obtained qualitatively agree with observations with the Hinode space observatory. 相似文献
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上海及邻区新构造应力场初步探讨 总被引：3，自引：0，他引：3
本文从活动断裂、水系分布方向、地震震源机制解三个方面,对上海及邻区新构造应力场进行了探讨。从新构造期活动断裂的力学性质分析,本区主压应力场方向为北东东至近东西;从水系河谷分布的优势方向推论出的主压应力场方向为96°左右;用本区56个地震震源机制解的 P轴赤平极射投影的极点统计分析法,确定主压应力方向约为80°;三者大体一致,说明它们是同一构造应力场的产物,其主压应力场方向为近东—西向。 相似文献
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通过对陕西耀州窑遗址内4个古窑,临潼兵马俑一号坑,西铜一级公路经过黄堡工地开挖的两个五代窑,以及耀州窑博物馆仓库工地内开挖的一个金代窑和一个春秋窑遗址的古地磁研究,初步得出了西安地区古地磁场变化的规律,为鉴定从春秋到金代西安地区的古遗址、古文物提供了考古地磁学上的一个粗略的标准。 相似文献
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The voltage stability problem in long-distance transmission systems can be exacerbated by geomagnetic disturbance (GMD) even in middle and low latitude areas where the effects of GMDs are considered to be mild compared to auroral areas. With the high voltage and the long-distance transmission lines, power system in China has to face the voltage instability risk. To clarify and measure the risk from GMD represented by geoelectric field, method for analysis of relationship between voltage stability of the long-distance transmission system and the size and direction of geoelectric field is provided. On the basis of calculation for geomagnetically induced currents (GICs) of power system and the additional reactive power losses of transformer due to GIC, the model of long-distance transmission line affected by geoelectric field is established. To measure the impact on the voltage stability of power system and the sensitivity of voltage to geoelectric field, the voltage stability index and the set of voltage limit violation nodes are proposed and calculated considering different geoelectric field and different initial operation conditions of power system. By taking the Northwest 750 kV power system in China as an example, voltage stability with geoelectric field magnitude from 1 V/km to 10 V/km, direction (0°) from north to south (180°) is analyzed and the voltage stability index is calculated, and the set of voltage limit violation nodes are summarized as well. The results show that the method is feasible and the index can reflect actually the relationship between the long-distance transmission system voltage stability and the geoelectric field, and the set of the voltage limit violation nodes can indicate which nodes are most susceptible to GMD. 相似文献
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Yu. V. Glagolevskij 《Astronomy Reports》2013,57(1):56-64
Measurements of the longitudinal magnetic field of the CP star HD 62140 with high accuracy (σ ～ 50 G) are used to construct a magnetic-dipole model for this star. The model describes the observed phase dependence of the field very well, supporting the idea that CP stars have dipolar magnetic fields. Based on an analysis of the CP stars HD 32633 and HD 142301, which were earlier suggested to have dipoles shifted perpendicular to the dipole axis, it is concluded that the only possible models in this case have one or two shifted dipoles, with the distance between the monopoles being comparable to the stellar radius. Such configurations may occur as a consequence of deformations of the field in early stages of the star’s evolution, due to the accretion of higher-mass objects or a merger with another component, as well as the influence of a convective core. 相似文献
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反演地壳磁化强度等效源法的模型验证及实际资料试算 总被引：1，自引：0，他引：1
等效源法曾被广泛应用于卫星磁异常解释,而本文是将等效源法引用到航空△T磁场的解释中,用其研究区域地质构造。根据等效源法的理论,推导出球坐标系下球棱柱体的△T磁场公式,采用线性反演的方法进行模型验证,同时将该方法用于秦巴地区航空△T磁异常的试算,得到了一些有意义的结论。利用该方法可由所求得的磁场强度来得到居里深度分布。 相似文献
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在位场数据边界识别传统方法理论的基础上,前人研究了各种场源边界增强技术来提高信噪比和定位精度,但仍然存在受噪声影响大、场源边界不够收敛等问题。本文在传统边界识别方法的基础上进行改进,利用小波变换与传统方法相结合来增强对噪声的压制能力,并且提出了幂次变换法对识别出的边界进行有效收敛。将改进方法与传统方法应用于地质体的边界识别;同时选取3种传统数值计算方法,结合模型数据、四川盆地重力异常数据及朱日和地区磁异常数据进行对比分析。结果表明：小波结合幂次变换法能够有效识别出研究区域内地质体的边界,能很好地起到压制噪声的作用;并且识别出的边界收敛,提高了边界识别的精度,在边界识别中取得了良好的效果。 相似文献
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Mohamed Sharif Berguig Mohamed Hamoudi Jean Louis Lemouël Yves Cohen 《Arabian Journal of Geosciences》2013,6(4):1063-1072
In this work, we report a global mapping of vector lunar magnetic field based on new method of separation of internal and external fields. The magnetic measurements collected during the lifetime of lunar prospector (LP) extended mission during 1999 were strongly disturbed by the solar wind, a period which coincided with a maximum of the 23 cycle activity. The multiscale wavelength external fields were analyzed using spherical harmonic transform. The external field determined by inversion was then removed from each magnetic field component for each half orbit. To map the vector magnetic crustal anomalies, all LP magnetometer data collected at low altitudes in the three different lunar environments: (1) geomagnetic tail, (2) solar wind, and (3) geomagnetic sheath were processed using this new approach. The results obtained using these selection criteria allow us to get a global coverage of the lunar surface by the vector magnetic field at variable spacecraft low altitudes. To validate our mapping, we have developed and applied a method based on properties of potential fields functions. This method can be used to determine both horizontal north and east components using only vertical component. The validated lunar internal magnetic measurements obtained at variable spacecraft altitudes were then continued to a common altitude of 30 km using an inverse method. This mapping confirms firstly the nature of the crustal sources of lunar magnetic field and clearly shows that the strongest concentrations of anomalies are associated with high albedo and/or located antipodal to large young basins (Orientale, Serenitatis, Imbrium, and Crisium) of age about 3.9 Ga. 相似文献
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直流输电线路对磁测的影响 总被引：3，自引：0，他引：3
越来越多的远距离、大容量直流输电线路投入运行对线路附近地区的磁测工作产生了不可忽视的影响。本文阐述了直流输电线路的结构、线路磁场特征及对以地质找矿为目的的磁测工作的影响。对直流输电线路磁场在磁测图中的特点也做了讨论,列举了直流输电线路影响的实例。 相似文献
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The progressive development of mylonitic fabrics in a series of Torridonian sandstones and shales has been studied along traverses across the Kishorn Nappe. The fabrics developed have been investigated using the following techniques.
- 1. 1. Optical examination of thin sections.
- 2. 2. Measurements of the anisotropy of magnetic susceptibility.
- 3. 3. X-ray texture goniometry.
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A Green’s function solution of Laplace’s equation for the potential magnetic field in an external spherical region is found using the derivative of the potential along a selected direction as a boundary condition. A set of programs applying this solution to construct the potential magnetic-field lines in solar active regions based on the photospheric line-of-sight field component has been developed. The method is tested using some model fields, and the optimal step size is found for realistic conditions. The developed software is applied to four real solar active regions, adopting HMI/SDO magnetograms as the boundary conditions. The potential magnetic field in the chromosphere and corona have been reconstructed for the selected regions. The calculated field lines are compared with flux tubes observed by AIA/SDO in the EUV. This comparison is used as a basis to discuss the applicability of a potential field approximation to the magnetic fields in solar active regions. 相似文献
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将磁偶极子在导电水平圆柱体的场分解为单磁极的一次场、二次场、柱内场、柱外场。然后,由两个单磁极的场叠加而得到磁偶极子的场,并编程序对总场的频率响应函数的虚实分量二次磁场分别做了计算。 相似文献
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We consider the properties of electric and magnetic fields in vacuum in the neighborhood of static, spherically symmetric
wormholes. Although certain aspects of this problem have been considered before, some important features remained undiscovered.
We study in detail the properties of electric and magnetic fields in the case of quasi-adiabatic motion of field sources near
an Ellis-Bronnikov wormhole and the passage of such sources through the wormhole. An exact solution is found in closed form
for a wormhole immersed in a magnetic field that is homogeneous at infinity, as well as an exact solution for a dipolar field
without sources. The properties of electromagnetic fields are important for possible observational manifestations of wormholes
in astrophysics. 相似文献