共查询到20条相似文献，搜索用时 31 毫秒
1.
The dipole model of the main geomagnetic field sources has been developed by the authors for several years. At present, the model includes 13 sources that existed and continuously developed during the 20th century. It has been assumed that the main dipole motion can be related to the motion of the Earth’s axis of inertia. At the same time, the known sharp changes in the direction of this motion, the so-called “wanderings” of the axis of inertia coincide in time with a change in the coordinates of the exit point of the main dipole magnetic moment vector on the Earth’s surface, dependent mostly on changes in the vector inclination. The motion of the north magnetic pole has been studied based on the model. It has been obtained that the dynamics of the main dipole parameters and, mainly, a stable variation in the inclination of the magnetic moment vector are responsible for the westward pole motion. At the same time, the observed rapid northward motion of the pole is related to the time variations in the parameters of 12 sources approximating the so-called nondipole part of the main field. 相似文献
2.
S. P. Burlatskaya S. F. Burlatsky A. F. Burlatsky S. A. Didenko 《Izvestiya Physics of the Solid Earth》2006,42(6):510-520
It was shown in our previous works that the dipole part of the geomagnetic field direction is mainly represented by the 1200-yr variation. According to some indications, the residual of the dipole part of the field, the so-called δ variation, may be classified as standing waves. Average values of δ are calculated for each hemisphere. In this work, the difference values equal to the δ variations for each territory minus δ averages over hemispheres (western or eastern) are calculated. The resulting values, fine structure (FS) variations, characterize the FS of the geomagnetic field. The study of the activity of the FS variations and specific features of their N-S and E-W behavior and the comparative analysis of dynamic characteristics (activity and rate) give grounds to classify the FS variations (as well as the δ variations) as standing waves of the nondipole field. 相似文献
3.
Michel Prévot 《Physics of the Earth and Planetary Interiors》1977,13(4):342-345
Directional and paleointensity data for the Steens Mountain geomagnetic polarity transition do not agree with the two simplest models of reversals: rotation of undiminished dipole or gradual diminution followed by change in polarity of the dipole moment. Instead, large and rapid changes in the intensity and direction of the field occur, probably as a result of non-dipole variations. 相似文献
4.
在空间域偶层位法的基础上,研究了完整的频率域偶层位曲面位场处理和转换方法.该法可应用于平面或曲面、规则网或非规则网的位场数据处理和转换.通过对偶层面z坐标和计算面z坐标平移不同的量来加速正演快速收敛和保证反演稳定、快速收敛;提出了适合于不规则网曲面处理和转换的核心算法——单点快速Fourier变换;提出了频率域不规则网曲面处理和转换方法技术.通过以上技术措施解决了大数据量特别是曲面不规则网的位场处理和转换问题,模型试算以及实际资料处理验证了该方法的应用效果. 相似文献
5.
M. N. Ramanaiah Chowdary 《Pure and Applied Geophysics》1971,92(1):139-149
Summary Not infrequently, in mining geophysics, the anomalous field of the magnetized body is appreciably large and it varies from the direction of the earth's normal field within the vicinity of the magnetized body. Total magnetic intensity data collected on the ground over shallow magnetized bodies cannot be interpreted quantitatively, since all the available methods of interpretation assume that the resultant field lies in the direction of earth's normal field as the anomalous field is small. For geological bodies that can be magnetically represented by infinite line pole, point pole, infinite line dipole, and point dipole, this paper gives quantitative interpretation procedures for total magnetic intensity anomalies without the above assumption using the characteristic points from the theoretical curves (not reproduced). These characteristic curves can be used for the direct determination of depths and offsets by using information from suitably chosen field profiles.Contribution No. N.G.R.I.-71-233. 相似文献
6.
1900~2000年的IGRF(国际地磁参考场)资料使研究20世纪中地磁场的变化规律成为可能,在20世纪中,即使从19世纪起,地球偶极子磁场发生了较大的变化,偶极矩一直保持衰减的势头,地心轴的所有3个分量都是减小的.地磁南极的位置变化在1930年左右发生大的转折,1960年起向西和向南快速移动,偶极子轴在纬度方面变化只有1°左右,经度变化在3°左右,离磁极倒转的条件差得远. 相似文献
7.
本文首先制作了TI地层模型井,对模型井的速度、密度等物理参数进行了测量,通过快速模拟退火算法得到了该介质的五个TI刚性系数,然后采用缩尺的偶极子探头在HTI地层井孔内进行超声测量实验模拟了实际的偶极子声波测井,并结合数值模拟的结果,研究了不同偏振方向的声源在HTI地层井孔中进行偶极子声波测井的响应特征.模拟结果表明,弯曲波的幅度和速度随声源的偏振方向不同而不同.正交分量的波形幅度在声源偏振方向平行或垂直于快横波面方位时最小,在与快横波面方位呈一定夹角时较大;同向分量波形幅度随声源的偏振方向的变化规律同正交分量相反.弯曲波速度在声源的偏振方向与快横波面方位的夹角小于30°或者大于60°时,分别接近于快弯曲波和慢弯曲波的速度,对于夹角的变化不敏感;当夹角在30°和60°之间时,弯曲波的速度对该夹角变化非常敏感,由接近快弯曲波速度快速变化到接近慢弯曲波速度. 相似文献
8.
A. N. Khramov 《Izvestiya Physics of the Solid Earth》2007,43(10):800-810
The paper analyzes previously published results of studies of detailed records of geomagnetic reversals in sedimentary and volcanic sequences of the Paleozoic in the Siberian and Eastern European platforms. It is shown that the processes of geomagnetic reversals, both in the Early Paleozoic and at the end of this era, are well described by a model in which the transitional field is controlled by an equatorial dipole. During a reversal, this dipole maintained a magnetic field at the Earth’s surface whose intensity amounted to about 20% of the intensity before and after the reversal. The equatorial dipole existed before and during the reversal and was responsible for the deviation from antipodality of paleomagnetic poles of adjacent polarity chrons (the so-called reversal bias). The position of the equatorial dipole axis during the Paleozoic correlates with the supposed geometry of convective motions in the mantle at that time. 相似文献
9.
古地磁学使用的虚地磁极（VGP）是在地心偶极磁场假设下计算的,由于地球非偶极磁场的存在,VGP一般不同于真地磁极（RGP）.为了定量检验非偶极磁场对VGP的影响,本文利用国际参考地磁场模型IGRF 1900～2000,在全球5°×5°的“虚拟测点”网格上计算了VGP和RGP的位置,并求出两种磁极的经纬度偏差和二者的角距离.结果表明,南极地区VGP与GP的角距离最大,可达26°,南大西洋和欧亚大陆北部最大达到24°和18°,其余地区一般小于15°.VGP对RGP的偏差与地磁场分布有关：在非偶极磁场较弱的地区（如太平洋半球）,纬度偏差一般不大（≤10°）,但是在主要地磁异常区（如南大西洋和南极地区）,VGP对RGP的纬度偏差可达25°.VGP对RGP的经度偏差要比纬度偏差大得多,例如在欧亚大陆北部地区,经度偏差分布在-180°到180°的大范围内. 相似文献
10.
正交水平磁偶源是模拟天然场源的较好人工源,可以方便地实现可控源高频大地电磁张量测量.正交水平磁偶源的电磁场分布规律是野外工作布置的理论基础,为此计算了均匀大地模型正交水平磁偶源的电磁场.计算结果表明:电磁场水平分量在各个象限都有一相对低值带,对应的标量视电阻率形成了畸变带,但张量视电阻率畸变带消失;张量视电阻率曲线形态显示出近区的低阻、过渡区的高阻隆起和远区趋于真值的规律.通过野外试验验证理论计算结果,在无法准确确定地下介质电阻率参数的情况下,以天然电磁场计算的电阻率为参照对比研究了正交水平磁偶源电磁场的分布规律.试验结果表明:正交水平磁偶源与电偶源的电磁场同样的存在近区、过渡区和远区;在远区,正交水平磁偶源与测点的相对位置对张量测量结果几乎没有影响,即在远区可以在任何方位测量;正交水平磁偶源的布置要考虑收发距的影响,保证测量在远区进行. 相似文献
11.
An analytical expression is derived for the cutoff rigidity of cosmic rays arriving at a point in an arbitrary direction, when the main geomagnetic field is approximated by that of an eccentric dipole. This expression is used to determine changes in geomagnetic cutoffs due to secular variation of the geomagnetic field since 1835. Effects of westward drift of the quadrupole field and decrease in the effective dipole moment are seen in the isorigidity contours. On account of the immense computer time required to determine the cutoff rigidities more accurately using the particle trajectory tracing technique, the present formulation may be useful in estimating the transmission factor of the geomagnetic field in cosmic ray studies, modulation of cosmogenic isotope production by geomagnetic secular variation, and the contribution of geomagnetic field variation to long term changes in climate through cosmic ray related modulation of the current flow in the global electric circuit. 相似文献
12.
Magnetic field transforms with low sensitivity to the direction of source magnetization and high centricity 总被引：7，自引：0，他引：7
Magnetic data interpretation faces difficulties due to the various shapes of magnetic anomalies and the positions of their extrema with respect to the causative bodies for different directions of the source magnetization. The well‐known transforms — reduction to the pole, pseudogravity field, and analytic signal (total gradient) — help in reducing the problem. Another way to achieve the required effect is the transformation of magnetic data, ΔT or Z, into values of the anomalous magnetic intensity T. In this respect, we have found some transforms based on differential operators such as the gradient of T and its modulus R = |?T|, the Laplacian L = ?2T, the product T ?2T and its square root Q, and the Laplacian ?2(T2) and its square root E, to be useful. They are slightly sensitive to the magnetization orientation and their extrema occur above the sources. For a 2D anomaly of a homogeneous causative body, the proposed transforms do not depend on the inclination of magnetization. In the 3D case, such independence does not exist even for the elementary field of a point dipole. The influence of the magnetization direction is estimated by an integral coefficient of sensitivity. This coefficient takes values of up to 2.0 for ΔT or Z anomalies, while their transforms T, R, E, Q and L have values of less than 0.28, 0.29, 0.24, 0.16 and 0.07, respectively, i.e. on average, 10 times less. The estimation of the centricity is carried out using the relative deviation of the principal extremum of the anomaly or its transforms from the epicentre of the model body at a depth equal to 100 units. For a ΔT anomaly this deviation is up to 67%; for the L transform it is less than 8%; for Q, E, R and T it is less than 10%, 15%, 20% and 25%, respectively. The proposed transforms take only non‐negative values. With respect to their shape, the peripheral magnetic extrema are removed, the anomalous configuration is simplified and the resolution of complicated interference patterns is improved. Their calculation does not require additional data for the direction of magnetization, which is an essential advantage over the reduction‐to‐the‐pole and pseudogravity‐field transforms. A joint analysis of the measured field and its transforms T, E and L offers possibilities for more confident separation of the anomalous effects and direct correlation to their sources. The model tests performed and the 3D field applications to real magnetic data confirm the useful properties of the transforms suggested here. 相似文献
13.
A validation experiment, carried out in a scaled field setting, was attempted for the long electrode electrical resistivity tomography method in order to demonstrate the performance of the technique in imaging a simple buried target. The experiment was an approximately 1/17 scale mock‐up of a region encompassing a buried nuclear waste tank on the Hanford site. The target of focus was constructed by manually forming a simulated plume within the vadose zone using a tank waste simulant. The long electrode results were compared to results from conventional point electrodes on the surface and buried within the survey domain. Using a pole‐pole array, both point and long electrode imaging techniques identified the lateral extents of the pre‐formed plume with reasonable fidelity but the long electrode method was handicapped in reconstructing vertical boundaries. The pole‐dipole and dipole‐dipole arrays were also tested with the long electrode method and were shown to have the least favourable target properties, including the position of the reconstructed plume relative to the known plume and the intensity of false positive targets. The poor performance of the pole‐dipole and dipole‐dipole arrays was attributed to an inexhaustive and non‐optimal coverage of data at key electrodes, as well as an increased noise for electrode combinations with high geometric factors. However, when comparing the model resolution matrix among the different acquisition strategies, the pole‐dipole and dipole‐dipole arrays using long electrodes were shown to have significantly higher average and maximum values within the matrix than any pole‐pole array. The model resolution describes how well the inversion model resolves the subsurface. Given the model resolution performance of the pole‐dipole and dipole‐dipole arrays, it may be worth investing in tools to understand the optimum subset of randomly distributed electrode pairs to produce maximum performance from the inversion model. 相似文献
14.
S. P. Burlatskaya S. F. Burlatsky A. F. Burlatsky S. A. Didenko 《Izvestiya Physics of the Solid Earth》2006,42(3):207-224
The purpose of archaeomagnetic research is to investigate the structure of the geomagnetic field and its evolution. This paper is a study of this type. In our preceding studies, we divided the geomagnetic field into dipole and nondipole components. It was then shown that the dipole component consists of the predominant 1200-yr variation and the remainder δ. The δ variation is the subject of this paper. Detailed study and comparison of the characteristic features of two 1200-yr variations (the dipole and δ variations) in both the declination and inclination indicates that, according to most of their features, they can be assigned to different types of waves, namely, traveling waves (the dipole variation) and standing waves (the δ variation). Successive averaging in time and space yielded averaged data on δI and δD not only for various parts of the world (Europe, Asia, and America) but also for the western and eastern hemispheres. 相似文献
15.
Summary A statistical model of the geomagnetic field is derived, based on the assumption of an axial geocentric dipole field of strengthH
e at the equator perturbed by randomly directed components of constant magnitudeh. The model fits the dispersions found from an analysis of the 1945 field, and the ratioh/H
e obtained for this field and from the palaeomagnetic data both average to about 0.4. The model predicts that during reversal of the dipole field, the field intensity falls to between 0.2 and 0.4 of the steady field intensity, and this agrees with estimates made from the palaeomagnetic observations. 相似文献
16.
M.A. Mayhew 《Earth and Planetary Science Letters》1984,71(2):290-296
Long-wavelength anomalies in the total magnetic field measured by Magsat over the United States and adjacent areas are inverted to an equivalent surface layer magnetization distribution. The model is based on an equal-area dipole grid at the Earth's surface. Model resolution, defined as the closest dipole spacing giving a solution having physical significance, is about 220 km for Magsat data in the elevation range 300–550 km. The magnetization contours correlate well with large-scale tectonic provinces. A higher-resolution (200 km) model based on relatively noise-free synthetic “pseudodata” is also presented. An excellent inverse correlation between apparent magnetization and heat flow in the western U.S. is demonstrated. A new regional heat flow map derived indirectly from Magsat data shows nearly all the important thermal anomalies evidenced in previous published maps. Notably, the map predicts high heat flow in Nebraska and the Dakotas, suggesting the presence of a “blind” geothermal area of regional extent. 相似文献
17.
A. Bochev 《Pure and Applied Geophysics》1969,74(1):25-28
Summary The coordinates and the components of the dipole approximating to the highest possible degree the earth's magnetic field are determined minimizing a sum of squares of differences between the dipole field and the earth's magnetic field. Numerical results by the aid of a digital computer have been obtained for epoch 1932, 1937, 1942, 1945, 1950, 1955 and 1960 on the basis of magnetic data from 61 observatories. 相似文献
18.
19.
P. Hoyng D. Schmitt M. A. J. H. Ossendrijver 《Physics of the Earth and Planetary Interiors》2002,130(3-4):143-157
We present a detailed analysis of the Sint-800 virtual axial dipole moment (VADM) data in terms of an Ω mean field model of the geodynamo that features a non-steady generation of poloidal from toroidal magnetic field. The result is a variable excitation of the dipole mode and the overtones, and there are occasional dipole reversals. The model permits a theoretical evaluation of the statistical properties of the dipole mode. We show that the model correctly predicts the distribution of the VADM and the autocorrelation function inferred from the Sint-800 data. The autocorrelation technique allows us to determine the turbulent diffusion time τd=R2/β of the geodynamo. We find that τd is about 10–15 kyr. The model is able to reproduce the observed secular variation of the dipole mode, and the mean time between successive dipole reversals. On the other hand, the duration of a reversal is a factor 2 too long. This could be due to imperfections in the model or to unknown systematics in the Sint-800 data. The use of mean field theory is shown to be selfconsistent. 相似文献