共查询到20条相似文献，搜索用时 796 毫秒
1.
Summary Following the recent appearance of spherical harmonic coefficients for the potential of the geomagnetic field for epoch 1965.0, the strengths and axes for a dipole, quadrupole and octupole have been computed from first, second and third order spherical harmonic coefficients respectively. An interesting relation existing between the parameters of the dipole, quadrupole and geomagnetic eccentric dipole is also indicated. 相似文献
2.
Denis E. Winch 《Pure and Applied Geophysics》1967,68(1):90-102
Summary The notion of a dipole is generalized to the case of the fifth order spherical harmonic coefficients of the geomagnetic potential. The corresponding five axes and fifth order multipole strength are computed for ten epochs in the interval 1845 to 1965. 相似文献
3.
Summary From a smooth series of spherical harmonic coefficients for the geomagnetic potential, the corresponding multipole parameters have been calculated for five epochs from 1942.5 until 1962.5, at five year intervals. Changes in multipole parameters are discussed in relation to the secular variation field and to theSchmidt eccentric dipole. 相似文献
4.
D. E. Winch 《Pure and Applied Geophysics》1967,67(1):112-122
Summary The nine coefficients of fourth order spherical harmonic functions in the expression for the potential of the main geomagnetic field are used to derive the nine parameters of a fourth order multipole. These nine parameters consist of the strength of the multipole, and four unit vectors or axes. The points of intersection of the axes with the surface of the Earth are called poles. Although movements of the poles over the period 1829 to 1965 are masked by random errors in the spherical harmonic coefficients, all of the axes show eastward components of drift since 1829, but two have drifted westward in later years to return almost to their initial 1829 positions. The strength of the fourth order multipole has shown a general increase, amounting to some 30 per cent of the 1829 value. 相似文献
5.
R. Thompson 《Physics of the Earth and Planetary Interiors》1984,36(1):61-77
Spherical harmonic coefficients of the geomagnetic field, calculated from historical observations of declination, inclination and intensity, and from archaeomagnetic inclination results, have been used to produce a film of geomagnetic change since 1600 A.D. The non-dipole geomagnetic field is found to be constantly changing: no fixed or standing non-dipole features are observed. Non-dipole foci are seen to have lifetimes of a few hundred years. The westward drift, which was an important feature of the 18th and early 19th century geomagnetic field, was less pronounced in the 17th century. The growth, evolution, decay and replacement of non-dipole foci, but not their movement are found to have been the major features producing century-long secular directional magnetic variation. Most of the low degree and order spherical harmonic coefficients have changed significantly over the last few hundred years. In particular the change in sign of the axisymmetric quadrupole around 1837 A.D. is noted. Sustained, century-long, intensity changes, however, appear to have been dominated by variations in the intensity of the centred dipole, rather than by non-dipole field fluctuations. 相似文献
6.
7.
P. Márton 《Pure and Applied Geophysics》1970,81(1):163-176
Summary Recently excellent archeomagnetic data sequences have been bublished from several parts of the world. Using these sequences, an attempt is made to trace the secular variation of the virtual geomagnetic dipole field characterized by the three first order spherical harmonic coefficients
. The archeomagnetic data (declination, inclination and total intensity) are transformed into the first order coefficients mentioned by a simple mathematical method. The secular variations of these coefficients, however, contain both dipole and non-dipole components. The separation of these is also attempted.Paper presented at the IAGA Symposium, Madrid, September 1969. 相似文献
8.
The development of a regional geomagnetic daily variation model using neural networks 总被引：1，自引：0，他引：1
P. R. Sutcliffe 《Annales Geophysicae》1999,18(1):120-128
Global and regional geomagnetic field models give the components of the geomagnetic field as functions of position and epoch; most utilise a polynomial or Fourier series to map the input variables to the geomagnetic field values. The only temporal variation generally catered for in these models is the long term secular variation. However, there is an increasing need amongst certain users for models able to provide shorter term temporal variations, such as the geomagnetic daily variation. In this study, for the first time, artificial neural networks (ANNs) are utilised to develop a geomagnetic daily variation model. The model developed is for the southern African region; however, the method used could be applied to any other region or even globally. Besides local time and latitude, input variables considered in the daily variation model are season, sunspot number, and degree of geomagnetic activity. The ANN modelling of the geomagnetic daily variation is found to give results very similar to those obtained by the synthesis of harmonic coefficients which have been computed by the more traditional harmonic analysis of the daily variation. 相似文献
9.
10.
Gerhard Fanselau Heinz Kautzleben Otto Lucke Peter Mauersberger Kurt Sellien 《Pure and Applied Geophysics》1964,57(1):5-30
Zusammenfassung Es werden die Ergebnisse einer Berechnung des geomagnetischen Potentials in Form einer Reihenentwicklung nach Kugelfunktionen bis zur 15. Ordnung auf Grund der magnetischen Weltkarten für die Epoche 1945,0 vonE. H. Vestine und andern vorgelegt. Bei der Ableitung des Potentialausdrucks nach der Methode der kleinsten Quadrate wurden die Orthogonalitätseigenschaften der Kugelflächenfunktionen vollständig ausgenutzt.
Summary The results of the analysis of the main geomagnetic field for the epoch 1945.0 in a series of spherical harmonics to the 15th degree are presented. The analysis is based on the world magnetic charts derived byVestine et al. The coefficients of the potential are calculated by least-squares approximation taking advantage of the orthogonality of the spherical harmonics over discrete ranges.相似文献
11.
Wallace H. Campbell 《Pure and Applied Geophysics》1987,125(2-3):427-457
The electrical conductivity of the Earth's upper mantle can be inferred from geomagnetic quiet-day,Sq, variations recorded at the world's observatories using the, coefficients of a spherical harmonic analysis (SHA) that separate the external (source) and internal (induced) parts of the surface field. The conductivity profile determined from such an analysis can be sensitive to special characteristics of the quiet field itself as well as the separation techniques employed. This review of the Sq-analysis features critical to a conductivity derivation is pictorially presented along with the equations for application of theSchmucker (1970) technique to theSHA coefficients for a conductivity determination. Three examples illustrate the use of these equations with differentSq models. 相似文献
12.
S. V. Starchenko 《Geomagnetism and Aeronomy》2011,51(3):409-414
The large-scale harmonic magnetic-convective sources of the main geomagnetic field in the Earth’s core have been determined
for the first time. The determination is based on a complete system of eigenfunctions of the magnetic diffusion equation in
a homogeneously conducting sphere, which is surrounded by an insulator. The sources of the main geomagnetic field observed,
which is responsible for the distribution of the electric currents generating this field in the core, are expressed in terms
of large-scale eigenfunctions. In this case, the dipole sources are directly related to the observed geomagnetic dipole, whereas
the quadrupole sources are related to the quadrupole, etc. The time variations in the obtained sources are responsible for
individual spatiotemporal features in the generation or suppression of each Gaussian component of the observed geomagnetic
field. When the commonly accepted observational international geomagnetic reference field (IGRF) models were used to partially
reveal these time variations, it became possible to specify the estimate of the Earth’s core conductivity and determine the
minimum period that can separate us from the commencement of further inversion or excursion. 相似文献
13.
N.P. Benkova A.N. Khramov T.N. Cherevko N.V. Adam 《Earth and Planetary Science Letters》1973,18(1):141-147
Analytical models of the palaeomagnetic field have been constructed for a number of geological periods (Quaternary Neogene, Jurassic, Triassic, Permian and Permo-Carboniferous) by spherical harmonic analysis using the present-day world map as a basis and (for the earlier periods) using also a palaeogeographic reconstruction. The use of the palaeogeographic chart for the earlier periods simplifies the models, and its use appears to be valid. The low accuracy, small number and uneven distribution of palaeomagnetic data severely limit the conclusions which can be drawn from the analyses. Nevertheless the results for all periods indicate that throughout the past 300 million years the geomagnetic field has maintained its global structure, and has remained similar to the field of a dipole slightly shifted from the Earth's centre. It appears that there have not been any persistent systematic anomalies or variations in the Earth's magnetic field throughout that time, but rather that the field has been oscillating around a mean level not greatly different from that of the present epoch. 相似文献
14.
2009年12月,国际地磁学与高空物理学协会（IAGA）发布了第11代国际地磁参考场（IGRF-11）。第11代IGRF包括1900．0-2010．0年代（间隔为5年）共23个地磁模型与2010．0---2015．0年代地磁长期变化的预测模型,其中1900．0-1995．0年代模型的阶次为N=M=10,相应球谐系数的精度为lnT;2000．0—2010．0年代模型的阶次为N=M=13,其球谐系数的精度为0．1nT;而2010．0—2015．0年代地磁长期变化预测模型的阶次为N=M=8,其球谐系数的精度为0．1nT。本文概述了第11代国际地磁参考场及其2010．0年代地磁模型与2010．0--2015．0年代地磁长期变化的预测模型。 相似文献
15.
Kenneth A. Hoffman 《Physics of the Earth and Planetary Interiors》1981,24(4):229-235
A model of the reversing geodynamo based on the assumptions (1) that reversals start in a localized region of the core and (2) that upon its onset this reversed region extends, or “floods”, both north-south and east-west until the entire core is affected, has recently been shown to provide a generally successful simulation of existing paleomagnetic records of the Matuyama-Brunhes transition (Hoffman, 1979). In this paper the modelled solution is analyzed so as to reveal the behavior of the dominant Gauss coefficients during the transition. At the time of total axial dipole decay the controlling components are found to be a zonal octupole (g30) and a non-axisymmetric quadrupole (g21, h21). Given the distribution of sites corresponding to the available records of the Matuyama-Brunhes, the existence of a significant zonal quadrupole field component cannot be ruled out; however, the role of any equatorial dipole component can be neglected.Due to the presence of a significant low-order non-axisymmetric term in the analyzed transition field, the predicted minimum intensity experienced during the Matuyama-Brunhes is found to be dependent on both site latitude and longitude. In particular, over a mid-northern circle of latitude, the predicted minimum intensity is found to vary by more than a factor of three, averaging about 10% of the full polarity field strength.Although not a unique solution, the applicability of the findings from this analysis is not tied to the phenomenological model from which they were derived. More specifically, whether the above two-component non-dipole transitional field arises from assumed configurational changes of the reversing geodynamo (as is the case for the flooding model) or, alternatively, is considered to be a stationary (non-reversing) portion of the field during axial dipole decay and regeneration, has little effect on either the calculated path locality of the virtual geomagnetic pole or the minimum intensity experienced at a given site. These two possible situations, in principle, should be distinguishable given the future attainment of detailed paleomagnetic data corresponding to back-to-back (R → N and N → R) polarity transitions. 相似文献
16.
通过对欧洲及其邻近地区 MAGSAT 卫星黎明资料进行了处理,得到1°×1°卫星磁异常网格值。本文使用冠谐分析方法,计算该地区卫星矢量磁异常（ΔX,ΔY,ΔZ）冠谐模型。球冠极点位于33°N和26°E,球冠半角为40°.冠谐模型的截断指数为18。根据卫星磁异常冠谐模型和地磁场球谐模型 DGRF1980,计算卫星总强度磁异常（ΔF）的冠谐一球谐模型。根据卫星磁异常的理论模型,计算并绘制不同高度（300,400,500km）的理论卫星磁异常图。对冠谐模型和大磁异常进行了分析和讨论。 相似文献
17.
T. I. Zvereva 《Geomagnetism and Aeronomy》2012,52(2):261-269
Based on vector magnetic data from the CHAMP German satellite, average daily spherical harmonic models of the main geomagnetic
field to n = m = 10 have been constructed for the period from May 2001 to the end of 2009 at an interval of 4 days. The obtained 16 models,
which were averaged over half a year, have been used to calculate the coordinates of the north and south magnetic poles (the
points where magnetic field lines are vertical). The changes in these coordinates during these eight and a half years have
been traced. Both poles continue moving northward and westward. The north magnetic pole has traveled 400 km during this period.
The velocity of its motion has increased up to the year 2003, reaching 62.5 km yr−1, and then started decreasing and reached 45 km yr−1 by the end of 2009. In addition, the direction of motion changed from north-northwestward to northwestward; i.e., the pole
started turning slightly towards Canada. The south magnetic pole moved slower by an order of magnitude and has traveled 42
km during this period. The coordinates of the geomagnetic (dipole) poles and the eccentric dipole parameters have also been
calculated. The dynamics of these poles has been traced. 相似文献
18.
Y.C. Whang 《Physics of the Earth and Planetary Interiors》1979,20(2-4):218-230
The paper presents a three-dimensional quantitative model of Mercury's magnetosphere based on the entire combined set of observational data obtained from the first and third encounters of Mariner 10 with Mercury. The model assumes that the surface magnetic field of the planet Mercury consists of a dipole, a quadrupole and an octupole. The dipole moment of Mercury is 2.4 × 1022 G cm3, tilted 2.3° from the normal to the planetary orbital plane and having the same directional sense as that of the Earth. The intensity of the quadrupole moment is approximately 45% of the dipole, and that of the octupole moment 29% of the dipole. The model meets four critical tests: (1) it produces the smallest residuals among all existing models, (2) it can reproduce the crossing of a tail current sheet by Mariner 10, (3) all planetary field lines are confined inside the model magnetosphere, and (4) the size of the model magnetosphere agrees well with the magnetopause crossings directly observed from Mariner 10. The model can also be used to explain two observational features: (1) the plasma characteristics observed in different regions of the magnetosphere, and (2) the regions of quiet and disturbed signatures directly observed from Mariner 10. 相似文献
19.
根据1936年中国东部和中部地区的地磁测量资料，以及国际地磁参考场DGRF1935和DGRF1940，用冠谐分析方法计算1936年中国地磁参考场(CGRF)的冠谐模型. 冠谐模型的截断阶数为8，球冠极位于36°N和104°E，球冠半角为30°.CGRF1936比相应的国际地磁参考场能更好地表示中国地磁场的分布，本文计算的冠谐模型的均方偏差分别为104.9 nT(X分量)，84.8 nT(Y分量)和121.1 nT(Z分量). 根据地磁场的冠谐模型，绘制1936年中国地磁图(X，Y，Z，F)和异常磁场图(ΔX，ΔY，ΔZ，ΔF). 相似文献
20.
N. Ya. Maksimov 《Geomagnetism and Aeronomy》2006,46(5):635-637
A comparison of the time variations in the geomagnetic field characteristics (the u and aa indices of geomagnetic activity) with the variation in the solar magnetic dipole inclination shows close agreement between these variations. The linear correlation coefficients between the u and aa indices, the u index and solar magnetic dipole inclination, and the aa index and solar magnetic dipole inclination are 0.93, 0.45, and 0.49, respectively. This makes it possible to extend studying the IMF evolution in the 11-year cycle of solar activity to the 170-year period beginning from 1835. It has been indicated that the time variation in the heliospheric current sheet (HCS) surface deviation from the solar magnetic equator plane, calculated based on the actual HCS configuration, is in good agreement with the time variation in the amplitude of the Fourier series second harmonics in a harmonic analysis of the series of daily data on the IMF sign in the vicinity of the Earth. The linear correlation coefficient is 0.9 in this case. 相似文献