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1.
A polar magnetic substorm on 1974 September 11 was recorded by a two-dimensional array of 25 three-component magnetometers, so located that the westward ionospheric current passed over the array. The mean perturbation fields over five-minute intervals are presented at six representative epochs of the substorm, the first just before its onset and the sixth 21/2 hr later in the coda of the event. At four of the resulting 'time frames', the perturbation fields have been fitted, on a least-squares criterion, by calculated fields of three-dimensional current loops having downward field-aligned current at the east end of the ionospheric westward current, upward field-aligned current at the west end and closure in the magnetotail. The current density was constant across the width of each of these model currents. In three of the four time frames it proved necessary to introduce a bend to the northwest in the ionospheric current; this bend occurred within 27° (geomagnetic) west of geomagnetic midnight. An association with the Harang discontinuity is possible. The field-aligned current nearer to the array (in one time-frame the downward, east-end current, in two others the upward current at the west end) proved essential to secure any reasonable fit to the data. The ionospheric segment of the current loop moved at least 20° of longitude eastward, relative to the surface of the earth, between 07.48 and 08.58 UT. In this 70-min period the ionospheric segment moved at least 38° eastward relative to magnetic midnight. 相似文献
2.
Summary. The transient fields resulting from an abrupt current switch-off in a vertically oriented finite loop and a magnetic dipole above a permeable and conducting half-space have been investigated by Fourier methods, utilizing an appropriate Green's function. Two partial fields are identified, one 'radiative' and evanescent and one 'diffusive'. Asymptotic formulae for the diffusive field above the interface, applicable for late times, are developed, and from these the effects of height of the transmitting source and the permeability contrast are calculated. It is shown that for 'late enough' times and at sufficient distances the dipole formulae provide adequate approximations to the field due to a finite loop. 相似文献
3.
R. J. Banks 《Geophysical Journal International》1979,56(1):139-157
Summary. Many geomagnetic variation anomalies are probably caused by the channelling, through small-scale bodies, of electric currents induced in much larger conductors elsewhere. Consequently, the direct interpretation of anomalous magnetic fields by modelling the electromagnetic response of conductive structures may give misleading results. It is suggested that, rather than attempting to proceed directly from the electromagnetic fields to conductivity models, we should instead take the intermediate step of determining the distribution of anomalous current flow.
Maps of the anomalous fields over a conductive structure can be generated from inter-station transfer functions. If it is assumed that the internal currents are concentrated in a thin sheet at a specified depth, the equivalent current system in the sheet can be computed directly from the vertical magnetic field. The most straightforward method of performing this calculation is to compute the Fast Fourier Transform of the magnetic field data, and then to apply a wavenumber filter.
The presence of any vertical currents invalidates the thin sheet model. However, if the spatial distribution of a horizontal component of the anomalous magnetic field is also known, the presence of any vertical currents can be detected directly, and their position determined. The value of the methods is illustrated by applying them to the interpretation of a Geomagnetic Deep Sounding survey of the Kenya rift valley. 相似文献
Maps of the anomalous fields over a conductive structure can be generated from inter-station transfer functions. If it is assumed that the internal currents are concentrated in a thin sheet at a specified depth, the equivalent current system in the sheet can be computed directly from the vertical magnetic field. The most straightforward method of performing this calculation is to compute the Fast Fourier Transform of the magnetic field data, and then to apply a wavenumber filter.
The presence of any vertical currents invalidates the thin sheet model. However, if the spatial distribution of a horizontal component of the anomalous magnetic field is also known, the presence of any vertical currents can be detected directly, and their position determined. The value of the methods is illustrated by applying them to the interpretation of a Geomagnetic Deep Sounding survey of the Kenya rift valley. 相似文献
4.
A comparative study on the ionospheric current systems in the Antarctic and Arctic regions 总被引：1，自引：0，他引：1 
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下载免费PDF全文 ＡｃｏｍｐａｒａｔｉｖｅｓｔｕｄｙｏｎｔｈｅｉｏｎｏｓｐｈｅｒｉｃｃｕｒｒｅｎｔｓｙｓｔｅｍｓｉｎｔｈｅＡｎｔａｒｃｔｉｃａｎｄＡｒｃｔｉｃｒｅｇｉｏｎｓＸｕＷｅｎｙａｏ（徐文耀）（ＩｎｓｔｉｔｕｔｅｏｆＧｅｏｐｈｙｓｉｃｓ，ＡｃａｄｅｍｉａＳｉｎｉ... 相似文献
5.
Summary. The paper reports studies of the three-dimensional magnetospheric—ionospheric current systems which produced polar magnetic substorms on 1974 September 7 and September 18. The data were magnetic perturbation fields observed with a two-dimensional array of 23 three-component magnetometers located in western Canada beneath the auroral oval. In an earlier study of a substorm of September 11 (Bannister & Gough) the fields fitted calculated field for a Boström Type 1 current loop with field-aligned currents at east and west ends of the ionospheric segment, and with uniform current density across the width. The substorms here reported could not be modelled with uniform current density. An inverse method due to Oldenburg was therefore used to estimate current density distributions, and satisfactory fits of calculated to observed field resulted. Each substorm was modelled at six representative epochs. In general the principal ionospheric current seem by the array was westward. At four epochs of the September 7 substorm and throughout the September 18 substorm, significant eastward ionospheric current (or its equivalent in terms of the fields produced) was observed north of the westward electrojet. Northwestward bends in the ionospheric current segments were found at four epochs on September 7 and at three epochs on September 18. As in the September 11 substorm (Paper 1), these bends were either west of or close to magnetic midnight. In some cases the bends may follow the auroral oval, but in others they are sharper and may be associated with the Harang discontinuity. East of geomagnetic the ionospheric currents tend to run in a constant geomagnetic midnight latitude range. The developments of the three substorms, of September 7, 11 (Paper 1) and 18, are compared. They showed a variety of shifts in longitude, though all moved eastward relative to magnetic midnight. 相似文献
6.
Wallace H. Campbell 《Geophysical Journal International》1980,61(2):437-449
Summary. Currents in the 1.28 × 103 km Alaska oil pipeline, induced from the ionospheric, auroral electrojet, were measured at three sites, near Fairbanks, Paxson and Valdez, Alaska, using a gradient configuration of two fluxgate magnetometers. The observed pipeline current magnitudes, which reached 50 A during times of mild geomagnetic activity, displayed a linear relationship with the electric earth potential. Using the induction relationship between the electric and magnetic fields and the typical spectral composition of the geomagnetic field at high latitudes, I obtained a spectral appearance of the current that shows a maximum in the range of 4.5- to 10-min period. Near Fairbanks the pipeline current amplitudes, I (Amperes), could be represented, approximately, by I = 0.65 B x T −0.5 , where B x (nT) is the north—south geomagnetic field variation amplitude and T (min) is its apparent period. There is much less pipelines current at the sites south of Fairbanks. A previously established relationship between the local electric field and the planetary geomagnetic activity index, Ap , permitted a prediction of the pipeline current surge amplitudes in the Fairbanks region as approximately I = 5.0 Ap . Current surges larger than 500 A may be expected rather often in the Alaska pipeline during large geomagnetic storms. 相似文献
7.
D. Heslop 《Geophysical Journal International》2007,171(3):1029-1035
Recent conceptual models have attributed the weak depositional remanent magnetizations observed in natural sediments to flocculation processes in the water column. Magnetic particles included into flocs have not only to rotate themselves into alignment with the geomagnetic field but also the larger particles to which they are attached, making remanence acquisition an inefficient process. Alignment is hindered further when the magnetization vectors of the particles in any given floc partially cancel, reducing the overall magnetic torque. Existing numerical simulations of flocculation effects on depositional remanence formation have been limited to spherical bodies with translational and rotational motion acting independently of each other. In the case of non-spherical flocs, the translational and rotational motion are coupled and such bodies will describe a complex trajectory through the water column. Calculations will be presented that show the torque exerted on a non-spherical floc by the surrounding water can be orders of magnitude greater than the magnetic torque. Non-spherical flocs will, therefore, align less efficiently with the geomagnetic field and hydrodynamic effects may play an important role in controlling the magnitude of sedimentary remanence. 相似文献
8.
Mark Noel 《Geophysical Journal International》1986,84(2):445-454
Summary. This paper describes the magnetic remanence and susceptibility anisotropy of 42 samples of laminated clay from Peak Cavern. The sediments are shown to have acquired a stable remanent magnetization due to the depositional alignment of magnetite grains. The magnetic fabric data confirm the existence of alteration within a reddened surface layer. A record of geomagnetic secular variation in the underlying clay is compared to a dated lake sediment magnetostratigraphy to suggest that deposition occurred around 7000 yr bp . A method for estimating water current directions based on the remanence and magnetic fabric data is critically assessed before deducing the sense of palaeoflow in the cave. 相似文献
9.
The geomagnetic power spectrum 总被引：1，自引：0，他引：1
Stefan Maus 《Geophysical Journal International》2008,174(1):135-142
Combining CHAMP satellite magnetic measurements with aeromagnetic and marine magnetic data, the global geomagnetic field has now been modelled to spherical harmonic degree 720. An important tool in field modelling is the geomagnetic power spectrum. It allows the comparison of field models estimated from different data sets and can be used to identify noise levels and systematic errors. A correctly defined geomagnetic power spectrum is flat (white) for an uncorrelated field, such as the Earth's crustal magnetic field at long wavelengths. It can be inferred from global spherical harmonic models as well as from regional grids. Marine and aeromagnetic grids usually represent the anomaly of the total intensity of the magnetic field. Appropriate corrections have to be applied in estimating the geomagnetic power spectrum from such data. The comparison of global and regional spectra using a consistently defined azimuthally averaged geomagnetic power spectrum facilitates quality control in field modelling and should provide new insights in magnetic anomaly interpretation. 相似文献
10.
The S~p_q equivalent current system of the quiet day geomagnetic variation in the polar region is very complicated. It is composed of several currents, such as the ionospheric dynamo current and the auroral electrojet caused by the field aligned current. S p q is unsymmetrical in both polar regions. In this paper, the S p q current systems are analyzed in the corrected geomagnetic coordinates (CGM) instead of the conventional geomagnetic coordinates (GM), and the symmetries of the S p q current in different systems are compared. Then the causes of S p q asymmetry in the GM coordinates are discussed; the effects of each component in S p q are determined. 相似文献
11.
对位于布兰斯菲尔德海峡东北部的沉积物岩心D1-7进行了初步环境磁学和古地磁研究,获得了连续的相对地磁场强度和方向。沉积物岩性总体为灰色软塑性粘土,中下部出现一层黑色火山灰层。结合该孔沉积物和有孔虫AMS14C测年结果（王汝建等未发表资料）,相对地磁场强度及其方向提供了12 ka以来连续的定年标尺,其中相对地磁场强度与具有相似沉积速率的南美Laguna Potrok Aike湖泊记录对比提供了六个对比点;同时特征剩磁倾角和磁偏角提供了另外六个对比点。磁化率各向异性分析揭示了全新世早、中和晚期岩心所在位置底流（南极深层水~1000 m）发生了阶段性显著变化,同时磁性矿物含量、粒度、沉积物湿密度等也发生了相应的变化。这些环境磁学和沉积学的变化主要受控于南极相应纬度处的太阳辐射量以及与辐射量相关的夏季季风降水量的变化,降水量增加导致磁性矿物粒度变细。D1-7也记录了一些千年尺度旋回变化,但是南极地区目前缺乏与之相似分辨率的气候参数记录,无法进一步探讨这些气候事件的缘起和分布范围。对比发现,地磁场长期变产生的年龄与沉积物全样有机碳AMS14C测年结果之间存在系统的差异,在6 ka以来比有机碳年龄年轻,在6 ka之前则比有机碳年龄老。南极布兰斯菲尔德海峡内各种不同水体的混合以及在全新世全球升温背景下冰川的动态变化和由此引起的中、深层水变化,都是造成水体性质复杂的原因。而地磁场强度和方向变化则不受水体性质的影响,因此可以提供更合理的年龄信息。自12 ka至今,25 cm/ka的平均沉积速率表明南极布兰斯菲尔德海峡地区整个全新世内稳定和丰富的沉积物供应。 相似文献
12.
D. M. Willis 《Geophysical Journal International》1982,68(3):751-764
Summary. Attention is drawn to a direct analytic method of calculating the quadrupole parameters of a planetary main magnetic field. Following a brief survey of the general theory of magnetic multipoles, an explicit algorithm is derived for calculating the quadrupole moment and the directions of the two quadrupole axes, given the five spherical harmonic coefficients of the second degree. It is shown that the direct analytic method of calculating the quadrupole parameters yield results for the geomagnetic quadrupole that are in exact agreement with those obtained by the more usual iterative procedure. Moreover, the direct analytic method has the distinct advantage that it does not require approximate values of the quadrupole parameters to be specified in advance. The direct analytic method of solution is used to calculate the quadrupole parameters for three different models of the main field of the Earth at epoch 1975; these computations provide some indication of the current uncertainties in the geomagnetic quadrupole parameters. It is also pointed out that a pseudo-quadrupole moment, which has been used to compare the quadrupole strengths of different planetary magnetic fields, is not strictly consistent with Maxwell's classical definition of a quadrupole moment. A precise physical definition of this pseudo-quadrupole moment is propounded. 相似文献
13.
Jean-Claude Mareschal 《Geophysical Journal International》1981,66(3):535-552
Summary. If one can measure the anomalous horizontal magnetic field associated with a (locally bounded) two-dimensional conductivity anomaly, the transfer function which results from correlating the vertical with the anomalous horizontal magnetic field directly indicates the depth to an equivalent line-current. A. numerical model can be used to illustrate this. If three-dimensional effects (including current channelling) produce the current anomaly, interpretation in terms of conductive structure would be less clear. It has been claimed (Babour & Mosnier etc.) that such three-dimensional effects are experimentally observed in the highly coherent transfer functions determined from differential geomagnetic sounding experiments. These effects are, specifically, the 'linear polarization' of the anomalous fields, and the invariance of the phase of the measured anomalous field across the anomaly. It is suggested in this present paper that both these effects can be explained in terms of simple local induction models.
If the embedded two-dimensional anomaly is sufficiently close to the Earth's surface, the transfer function (between the vertical and the total horizontal field) contains more information than is usually interpreted. With this in mind, the magnetovariational data collected by Rooney & Hutton in the Kenyan Rift is re-examined. 相似文献
If the embedded two-dimensional anomaly is sufficiently close to the Earth's surface, the transfer function (between the vertical and the total horizontal field) contains more information than is usually interpreted. With this in mind, the magnetovariational data collected by Rooney & Hutton in the Kenyan Rift is re-examined. 相似文献
14.
On the interpretation of frequency response functions for oceanic gravity and bathymetry 总被引：1，自引：0，他引：1
Neil M. Ribe 《Geophysical Journal International》1982,70(2):273-294
Summary. In 1972–78, the late N. D. Watkins and others carried out ajoint field programme of geological mapping in the Mio-Pliocene flood basalts of Iceland, including sampling for K-Ar dating and palaeomagnetic research. The major part of the palaeomagnetic sampling is represented by 2462 lavas in five long composite sections through the lava pile. This paper deals with various statistical properties of this data set.
It is concluded that geomagnetic reversals occur more frequently than is assumed in the current ocean-floor polarity time-scale. There is no evidence for significant asymmetries between normal and reverse polarity states of the field, neither as regards chron lengths, secular variation, or virtual dipole moment magnitude. Intensities of remanence in these lavas are shown to be well approximated in terms of a hyperbolic distribution. The latitude distribution of virtual magnetic poles can be fitted with a Bingham function having k' ∼ 4.5, and low-latitude poles do not occur preferentially in any particular longitude interval. 相似文献
It is concluded that geomagnetic reversals occur more frequently than is assumed in the current ocean-floor polarity time-scale. There is no evidence for significant asymmetries between normal and reverse polarity states of the field, neither as regards chron lengths, secular variation, or virtual dipole moment magnitude. Intensities of remanence in these lavas are shown to be well approximated in terms of a hyperbolic distribution. The latitude distribution of virtual magnetic poles can be fitted with a Bingham function having k' ∼ 4.5, and low-latitude poles do not occur preferentially in any particular longitude interval. 相似文献
15.
Piezomagnetic potentials due to an inclined rectangular fault in a semi-infinite medium 总被引：2，自引：0，他引：2
Mitsuru Utsugi Yasunori Nishida & Yoichi Sasai 《Geophysical Journal International》2000,140(3):479-492
Analytical solutions for the piezomagnetic potentials are derived for strike-slip, dip-slip and tensile-opening fault motions with arbitrary dip and strike angles, so as to be applicable in various types of earthquakes. These solutions are expressed as the composition of elementary functions which are identical to the magnetic potentials produced by magnetic dipoles, quadrupoles and octupoles distributed on the fault plane and other planes. Therefore, the geomagnetic field changes due to the piezomagnetic effect are expressed by the superposition of the fields produced by these equivalent sources.
Examples of calculated results show characteristic features for various types of fault motions as follows: (1) the pattern of the geomagnetic field changes becomes significantly different depending on the strike direction, although the maximum amplitude is almost the same for all directions; (2) the geomagnetic field change reaches a maximum at a dip angle of 90° for strike-slip and tensile-opening fault motions and at 45° for dip-slip fault motion. 相似文献
Examples of calculated results show characteristic features for various types of fault motions as follows: (1) the pattern of the geomagnetic field changes becomes significantly different depending on the strike direction, although the maximum amplitude is almost the same for all directions; (2) the geomagnetic field change reaches a maximum at a dip angle of 90° for strike-slip and tensile-opening fault motions and at 45° for dip-slip fault motion. 相似文献
16.
William Lowrie Walter Alvarez Isabella Premoli Silva Simonetta Monechi 《Geophysical Journal International》1980,60(2):263-281
Summary. A record of geomagnetic field polarity for the Barremian, Aptian and Albian stages of the Early Cretaceous has been derived in three over-lapping sections of pelagic carbonate rocks in the Umbrian Apennines of northern Italy. The remanence carrier in the greyish-white Majolica limestone and Fucoid Marls is magnetite, with haematite also an important constituent in a zone of 'couches rouges' within the Fucoid Marls. The weak remanent magnetizations were measured with a cryogenic magnetometer. Alternating field or thermal demagnetization was used to isolate the characteristic remanent magnetization (ChRM) in 655 specimens from 248 stratigraphic levels. The samples respond positively to a tectonic fold test, indicating that the ChRM predates the Late Tertiary folding of the Umbrian sequence. The magnetic stratigraphy derived from variations of virtual geomagnetic pole latitude clearly defines the recognizable reversal pattern associated with Mesozoic marine magnetic anomalies M0 to M4. The sections have been zones palaeontologically on the basis of planktonic foraminifera and calcareous nannofossil assemblages. The ages of magnetic anomalies M0 to M4 determined in this way are somewhat older than those in the reversal time scale of Larson & Hilde (1975). Anomaly M0 is located in the Early Aptian, close to the Aptian/Barremian boundary. A long period of normal polarity in the Aptian and Albian corresponds to the early part of the Cretaceous magnetic quiet zone. It is interrupted in the Late Aptian by a reversal which we find in only one of the Fucoid Marl sections, and which has not been reported in oceanic magnetic anomaly investigations. 相似文献
17.
Summary. An exact equation is derived for the magnetic field lines of the general axisymmetric magnetic multipole of arbitrary degree ( n ). This new result has important applications in studies of the possible nature of solarterrestrial physics during geomagnetic polarity reversals. In the limiting case of a magnetic dipole ( n=1 ), the equation for the magnetic field lines of the general axisymmetric magnetic multipole simplifies correctly to the well-known dipolar form, which is used extensively in geomagnetism, magnetospheric physics and cosmic-ray physics as a first-order approximation to the actual configuration of the geomagnetic field.
It is also shown theoretically that suites of similar magnetic field lines of the general axisymmetric multipole attain their maximum radial distances from the origin on a set of circular conical surfaces, with coincident vertices at the centre of the Earth; this set includes the equatorial plane if the degree ( n ) of the multipole is odd. The magnetic field is horizontal everywhere on all these surfaces.
Palaeomagnetic studies have suggested that during some polarity reversals the magnetic field in the inner magnetosphere can be represented approximately either by a single, non-dipolar, low-degree (2 < n < 4), axisymmetric magnetic multipole or by a linear combination of such multipoles. In this situation, the equation for the field lines of an axisymmetric magnetic multipole of low degree (2 < n < 4) would be as fundamental to a proper understanding of magnetospheric, ionospheric and cosmic-ray physics during polarity reversals as is the equation for dipolar field lines in the case of the contemporary geomagnetic field. 相似文献
It is also shown theoretically that suites of similar magnetic field lines of the general axisymmetric multipole attain their maximum radial distances from the origin on a set of circular conical surfaces, with coincident vertices at the centre of the Earth; this set includes the equatorial plane if the degree ( n ) of the multipole is odd. The magnetic field is horizontal everywhere on all these surfaces.
Palaeomagnetic studies have suggested that during some polarity reversals the magnetic field in the inner magnetosphere can be represented approximately either by a single, non-dipolar, low-degree (2 < n < 4), axisymmetric magnetic multipole or by a linear combination of such multipoles. In this situation, the equation for the field lines of an axisymmetric magnetic multipole of low degree (2 < n < 4) would be as fundamental to a proper understanding of magnetospheric, ionospheric and cosmic-ray physics during polarity reversals as is the equation for dipolar field lines in the case of the contemporary geomagnetic field. 相似文献
18.
Summary. A precision magnetic survey for the investigation of current activity in the Earth's lithosphere has been carried out in the Urals and in the Carpathians. As a result of this research three types of time variation of the total field were discovered. These are:
(1) The normal field variation reflecting the general pattern of secular variation. The difference of initial and repeat observation where only this type of variation operates, is rather small and usually does not exceed 0.2–0.3 nT. The field changes in such regions can be used only to evaluate the observation errors and to provide the regional pattern of secular variation.
(2) The slow but localized'anomalous field'change from year to year corresponding, presumably, to anomalies of a tectonomagnetic nature. The normal pattern of the secular variation field here is disturbed by sources located in the upper part of the lithosphere.
(3) Irregular time changes of the field with rather large amplitudes (up to 10–20 nT). Repeated observations of such anomalies show that the field changes significantly here even during one day. Both in the Urals and Carpathians these anomalies form extended elongated structures with widths up to 10–30 km. These anomalies usually coincide with those deep faults where the strongest recent crustal movements have been determined by means of geodetic observations. The analysis of the results of precision geomagnetic surveys in the Urals and in the Carpathians shows that geomagnetic investigations can be used for the exploration of tectonically active zones. 相似文献
(1) The normal field variation reflecting the general pattern of secular variation. The difference of initial and repeat observation where only this type of variation operates, is rather small and usually does not exceed 0.2–0.3 nT. The field changes in such regions can be used only to evaluate the observation errors and to provide the regional pattern of secular variation.
(2) The slow but localized'anomalous field'change from year to year corresponding, presumably, to anomalies of a tectonomagnetic nature. The normal pattern of the secular variation field here is disturbed by sources located in the upper part of the lithosphere.
(3) Irregular time changes of the field with rather large amplitudes (up to 10–20 nT). Repeated observations of such anomalies show that the field changes significantly here even during one day. Both in the Urals and Carpathians these anomalies form extended elongated structures with widths up to 10–30 km. These anomalies usually coincide with those deep faults where the strongest recent crustal movements have been determined by means of geodetic observations. The analysis of the results of precision geomagnetic surveys in the Urals and in the Carpathians shows that geomagnetic investigations can be used for the exploration of tectonically active zones. 相似文献
19.
CHARACTERISTICS OF Sq VARIATION OF GEOMAGNETIC FIELD AT THE GREAT WALL STATION, ANTARCTICA IN WINTER 下载免费PDF全文
下载免费PDF全文 《极地研究》1991,2(1):53-59
In this paper the characteristics of Sq variation of geomagnetic field in the region of the Chinese Great Wall Station (CGWS), Antarctica, in winter are analyzed from geomagnetic data obtained at the Geomagnetic Observatory of CGWS. The result enables us to reveal the following aspects: (1) The pattern of Sq variation at CGWS in early (Apr.) and Late winter (Sep.) is similar to that at Beijing Geomagnetic Observatory (BJO) at the middle latitude in the Northern Hemisphere. It may be controlled by the midlatitudinal ionospheric dynamo current. Amplitude of Sq variation is very small, and the harmonics in 8 hours or shorter periods in midwinter (June and July) is predominant because of the decreased effect of solar ultraviolet radiation and the dominant geomagnetic disturbance at high latitudes. (2) The vectors of Sq-equivalent current in the daytime are about five times more than that in the night. The direction of the vectors is clockwise in the daytime (08-15h) and counterclockwise in the night in earl 相似文献
20.
本文利用南极长城站1987年4月至9月的地磁资料,分析了长城站地区冬季地磁S_q变化特征。分析结果表明:(1)南极长城站在初冬(4月)与冬末(9月)月份的S_q变化形态与北半球中纬度的北京地磁台的S_q变化形态基本相似,这可能是由中纬度电离层中的发电机电流所控制的。在仲冬月份(6月与7月),由于太阳紫外辐射效应减少,高纬度的地磁扰动占主导地位,反映出S_q变幅很小和以8小时以下的较短周期谐波起主要作用,(2)在初冬与冬末月份的S_q等效电流矢量,白天比黑夜大约5倍;其矢量方向在白天(08—15时)为顺时针,黑夜为反时针。在仲冬月由于电离层中电流的影响相对减弱,S_q等效电流矢量很小,白天与黑夜基本一样;其矢量分布方向与初冬和冬末的矢量方向不同,这可能是极区的电离层电流或场向电流的影响造成的。 相似文献