中国地区地磁长期变化研究

采用2000~2004年中国地区34个台站的地磁日均值数据, 计算了通日和静日的平均年变率,以及静日的拟合年变率.应用上述年变率, 建立了2000.0~2005.0年代中国地区地磁场长期变化泰勒多项式模型和曲面样条模型.分析讨论了该泰勒多项式模型和曲面样条模型与国际地磁参考场长期变化模型(IGRF-SV)的异同, 结果表明,中国地区地磁长期变化的泰勒多项式模型与曲面样条模型的形态与数值是一致的,而且与IGRF-SV长期变化的趋势也是一致的,但中国地区地磁长期变化具有区域特征.     

Helical core flow from geomagnetic secular variation

Fluid flow below the core-mantle boundary is inferred from geomagnetic secular variation data, assuming frozen magnetic flux and a new physical assumption termed helical flow, in which the tangential divergence correlates with the radial vorticity. Helical flow introduces streamfunction diffusion and removes non-uniqueness in the inversion of the magnetic induction equation. We combine helical flow with tangential geostrophy and compare the following physical assumptions: tangential geostrophy, strong helicity, weak helicity and columnar flow, using geomagnetic field models from the 2000 Oersted and 1980 Magsat satellites. Our solutions contain some features found in previous core flow models, such as large mid-latitude vortices, westward drift in most of the southern hemisphere, and suggested polar vortices. However, our solutions contain significantly more flow along contours of the radial magnetic field than previous core flow models.     

地磁场长期变化和日长十年尺度变化的周期特征

根据历史地磁场模型GUFM1、第10代国际参考地磁场（IGRF10）模型和日长资料,采用小波变换方法,分析了地磁场磁矩、能量、西向漂移等参数的长期变化和日长十年尺度变化的周期分量及其时变特征.结果表明,1800～2005年期间,偶极子磁场长期变化有82年和48年准周期分量,它们与日长变化的周期没有直接关系.非偶极子磁场参数的长期变化与日长变化有66年和32年准周期分量,66年准周期比32年准周期强.在66年准周期分量,西向漂移比日长变化超前8.8年,非偶极子磁场能量比日长变化滞后15.6年.日长十年尺度波动和地磁场长期变化的起源不存在因果关系.     

A note on the secular variation of the geomagnetic field

Geomagnetic variations with (apparent) periods from 13 to 30 y have been reported by Alldredge (1977) who has argued that the origin of these signals must be found in the core of the Earth rather than outside the Earth. It is shown in this paper that a portion of these geomagnetic variations (perhaps most of the variations) might well be due to geomagnetic signals of much longer period, originating in the core, that appear to have periods of 13–30 y because of an artifact of the data processing. Much of the remainder of these variations could well be of external origin. A method for processing these data is suggested that is superior to Alldredge's method in minimizing the generation of spurious waves by long-period secular variation.     

The effect of solar activity on the secular variation of the geomagnetic field in Romania

The 11-year solar cycle effect in the geomagnetic components H and Z is made clear for Surlari Observatory and 19 repeat stations for the interval 1952–1974. The correlation with Wolf number and its time derivative is discussed in terms of the effects of the external and induced current systems.The $\text{H}\text{?}$ data available for solar cycle 20 (1964–1976) were processed to give the geographical distribution of the secular variation impulse for epoch 1969.5 in Romania. It is suggested that this distribution might reflect the deep internal structure of the area considered.A qualitative correlation is noted between long-period solar activity and variation of the horizontal component of the geomagnetic field at some repeat stations.     

地磁场长期变化特征及机理分析

将地磁场的总变化分为三部分：偶极场自身变化,非偶极场自身变化及非偶极场磁斑区通过对核幔边界（CMB）层环形电流的调制来影响偶极场的变化. 本文利用国际地磁参考场模型IGRF）1900～2000计算分析了地球不同深度地磁场分布及长期变化特征,且讨论了变化的可能机制. 可以推论,地磁场西漂和倒转不仅是非偶极场引起,同时与偶极场有密切关系.     

Palaeomagnetic evidence for stationary sources of geomagnetic secular variation

Asymmetrical curvilinear patterns of secular variation with approximately superposed “outward” and “return” trajectories can be attributed to stationary magnetic sources in the core. Some appropriate palaeomagnetic examples are presented here.     

主磁场长期变化十年至百年尺度的周期

本文运用小波变换技术,通过分析历史地磁场模型gufm1（时间跨度从1590~1990年）,考察主磁场长期变化场（B场）的周期性.结果表明,B场总磁极强度存在三个主要的周期分量：稳定的30年周期,在偶极子场的赤道分量g11和非偶极子场中较常见;频散的准50年周期,主要是由轴向偶极子分量g01贡献的,此外,四极子场也有贡献;世纪尺度的110年周期,其强度会发生变化,主要来源于偶极子场的赤道分量以及八极子场.     

Physical constraints for the analysis of the geomagnetic secular variation

Slow changes in the magnetic field are believed to originate in the core of the Earth. Interpretation of these changes requires knowledge both of the vertical component of the field and of its rate of change at the core-mantle boundary (CMB). While various spherical harmonic models show some agreement for the field at the CMB, those for secular variation (SV) do not. SV models depend heavily on annual means at relatively few and poorly distributed magnetic observatories. In this paper, the SV at the CMB is modelled by fitting 15-year differences in the annual means of the X, Y and Z components (from 1959 to 1974). The model is made unique by imposing the constraint that $\text{?}{}_{\mathrm{CMB}}\text{B}\text{?}{}_{\mathrm{r}}{}^2\text{d}\text{S}$ be a minimum, using the method of Shure et al. (1982). If SV is attributed to motions of core fluid, then this model will yield, in some sense, the slowest core motions. The null space is determined by the distribution of observations, and therefore, to be consistent, only those observatories have been retained which recorded almost continuously throughout the interval 1959–1974.The method allows misfit between the model and the observations. The best value for the misfit can be derived from estimates of errors in the data, or alternatively, because larger misfit leads to smoother models (i.e., smaller $\text{?}\text{B}\text{?}{}_{\mathrm{r}}{}^2\text{d}\text{S}$), the best value can be estimated subjectively from the final appearance of the model. Both procedures have their counterparts in the conventional spherical harmonic expansion approach, when smoothing is achieved by lowering the truncation level. The new proposal made in this paper is to use objective criteria for determining the misfit, based on the assumption that diffusion is negligible, in which event all integrals $\text{∫}\text{B}\text{?}{}_{\mathrm{r}}{}^2\text{d}\text{S}$ will vanish when S_i is a region on the CMB bounded by a contour of zero vertical component of field. For the 1965 definitive model which is adopted here, and for most other contemporary models, there are six such areas, giving five independent integrals (the integrals over the six regions must sum to zero if ? · B = 0). Tabulating these integrals for various choices of the misfit gives minimum values near 2 nT y^?1. It is impossible to achieve this good a fit to the data using a reasonable model derived by truncating the spherical harmonic expansion. The value 2 nT y^?1 corresponds to errors of ～ 20 nT in individual annual means, which is rather larger than expected from the scatter in the data.     

Modeling of the geomagnetic field secular variation based on the satellite surveys

The accuracy of the geomagnetic field secular variation (SV), obtained using different methods of analysis based on different data sets, has been estimated. A comparison of different SV models (developed by different groups of researchers) as candidates for compiling the IGRF 10th generation is the example of such an estimation. These models were obtained based on the Oersted and CHAMP satellite data. In the present work these models are compared in order to estimate the modeling algorithms and the effect of initial data selection on modeling results. To solve this problem, several SV models have been constructed based on the independent algorithms and data sets. The differences between the candidate models using different data proved to be of the same order. A comparison of the spatial power spectra indicated that all models constructed using data subjected to the frequency selection considerably differ from the models the data of which were not selected.     

用虚地磁极（VGP）方法对地磁场随时间变化的研究

首次引用古地磁学中虚地磁极（ＶＧＰ）的计算方法来研究现代地磁场的变化规律。通过对中国地区６个台站资料的分析以及对全球３９个台站资料的分析结果可以得出结论：利用地磁场角度分量来研究长期变化是可行的;ＶＧＰ的漂移情况正好表明非偶极子磁场的存在与随时间的变化;ＶＧＰ漂移方向的全球分布与地磁长期变化场的有关分量等值图之间的一致性较好。     

Late Quaternary secular variation of geomagnetic declination in western New York

A secular variation record of the geomagnetic declination has been obtained from glaciolacustrine varved clays and postglacial sediments, sampled both from outcrop and from piston cores from Lake Ontario. It appears to be uninterrupted and covers the interval 14,000 years B.P. (¹⁴C) to the present. The record for the interval 14,000–12,300 years B.P. consists of true declination and was obtained from samples collected from outcrop. The record for the interval 12,500 + years B.P. to the present consists of relative declination and was obtained from piston cores. The secular variation record is internally consistent and is compatible with the chronology of events known to have occurred during and following the deglaciation of western New York. Use of the record for magnetic correlation within the study area is demonstrated.     

地磁场长期变化速率的30年周期

地球主磁场B和它的长期变化都起源于地球外核的磁流体发电机过程,但是,它们的空间结构和时间演化特征却有很大差异. 本文采用全球平均的“无符号年变率”X〖DD(-*3〗〖KG*2/3〗·〖DD)〗〖DD(-*2〗〖KG*2/3〗—〖DD)〗、Y〖DD(-*3〗〖KG*2/3〗·〖DD)〗〖DD(-*2〗〖KG*2/3〗—〖DD)〗、Z〖DD(-*3〗〖KG*2/3〗·〖DD)〗〖DD(-*2〗〖KG*2/3〗—〖DD)〗、H〖DD(-*3〗〖KG*2/3〗·〖DD)〗〖DD(-*2〗〖KG*2/3〗—〖DD)〗和F〖DD(-*3〗〖KG*2/3〗·〖DD)〗〖DD(-*2〗〖KG*2/3〗—〖DD)〗来表征长期变化场〖WTHX〗〖AKB·〗〖WTBZ〗的总体强度,利用第9代国际参考地磁场模型IGRF 9,研究〖WTHX〗〖AKB·〗场的变化特征. 结果表明,在1900～2000年的100年当中,〖AKB·〗场经历了3幕变化,最大年变率分别发生在1910～1920、1940～1950、1970～1980年,显示出清晰的30年周期变化,而且,每一周期的上升段比其下降段短得多. 研究结果还表明,非偶极场对〖AKB·〗的贡献约为偶极场的2倍,因此,决定〖AKB·〗场周期特征的主要因素是非偶极场（特别是四极子场）,而不是偶极子场. 这一特点与主磁场B〖WTBZ〗中偶极场占绝对优势的特点完全不同.     

华南地区地磁场长期变化特征

使用华南地区5个国家基准地磁台2008—2018年地磁观测数据,通过对磁偏角D、磁倾角I、总强度F、北向分量X、东向分量Y、水平分量H、垂直分量Z月均值及年变率的分析,研究该区地磁场长期变化特征。结果表明,华南地区5个地磁台近10年来七要素月均值及年变率均呈缓慢变化趋势,且变化量相当,反映了该区域地磁场长期变化的特征。     

地磁长期变化信号提取和模型预测精度评估

高精度地磁场信息在地球物理导航等领域有着广泛应用,一般依靠地磁场模型来预测未来磁场的时空状态变化特征.本文基于中国大陆10个地磁基准台站2009—2022年的连续矢量观测数据,通过月均值年差分和主成分分析方法剔除外源干扰场,进一步去除岩石圈磁场,提取得到了主磁场长期变化信号,并将其与IGRF和WMM系列主磁场模型结果进行对比.通过引入绝对误差、均方根误差等指标,定量评估了IGRF-12和WMM2015模型在中国大陆区域内1—5年尺度的预测精度.结果表明,IGRF-12和WMM2015模型均能总体反映我国大陆主磁场长期变化趋势,两者总场强度的5年均方根误差分别为54.19 nT和15.86 nT,WMM2015模型预测的7个地磁要素的精度均优于IGRF-12.模型误差会随时间逐渐增大,两模型总场强度的1年期最大误差为13 nT,5年期最大误差可达153.65 nT,难以满足高精度定向钻井等领域的地磁导航需求,因此,有必要结合地磁台等观测资料,研制年周期地磁场快速长期变化模型.

     

20世纪地磁长期变化场分析

利用IAGA（国际地磁与高空物理学协会）编制的IGRF(国际地磁参考场)研究了20世纪地磁场变化规律. 20世纪地磁长期变化场的四极子（n=2的高斯系数所表示）变化最为显著,与主磁场相比长期变化场的球谐级数收敛较慢,利用追踪异常焦点位置随时间的变化的方法,发现地磁非偶极子长期变化场的垂直分量Z的等值图上有五大异常,其漂移情况不太统一,但是基本上是西向漂移.这种西向漂移的不一致性,在某种程度上证明了地磁场模型的正确性. 20世纪地磁场长期变化的能量谱与主磁场的不同,偶极子、 四极子和八极子的变化较明显.     

The secular geomagnetic variation. Statistical methods for paleomagnetic directions in sediments

Understanding the character of variations in the magnetic field of the Earth in the geological past requires a mathematically substantiated method for testing the statistical hypotheses against the real paleomagnetic data. As known, the paleomagnetic data from lava flows are sort of momentary snapshots of the state of the ancient magnetic field. Being quite fragmentary in time and space, these data compose what is referred to as a sample in statistics: on the close discrimination of the lava flows, the internal correlations in the data are absent. It is well known that the distributions of the paleomagnetic directions from the sedimentary data differ from the distributions in lavas, which is mainly due to the effect of averaging of the magnetization over the time interval corresponding to the accumulation of sedimentary layers represented in the rock specimen. Assuming the rate of sedimentation to be known for each specimen, one can suggest the method for the quantitative testing the statistical consistency of the paleomagnetic data in the sediments with the model variations of the magnetic field of the Earth in terms of the Giant Gaussian Process (GGP). It turned out that the averaging effect can well be allowed for by the coefficients of GGP, and the scheme of the further testing is in this case identical to the scheme of testing the paleomagnetic data obtained from lavas.     

CHAMP卫星主磁场长期变化和长期加速度的分布特征

本文利用CHAMP卫星磁测资料建立的新一代地磁场模型POMME-4.2S,分析了全球和中国地区地磁长期变化X、Y、Z、H、F、J、D 7个分量以及长期加速度X、Y、Z3个分量的分布特征,比较了POMME-4.2S长期变化模型与中国长期变模型CGRF-SV的磁异常分布差异.主要结果表明,地磁长期变化磁四极子起主要贡献,长期加速度变化磁八极子贡献最大.2004.0年全球长期变化的减小要比增加大得多,地磁场总体在减弱.长期加速度在中低纬度地区变化较大,高纬度地区变化小.Z和Y分量磁异常沿经度方向正、负交错形成几个大片区,X分量主要正负磁异常成对分布于赤道两侧.长期加速度X、Y、Z3个分量的磁异常分布存在明显的关系:在Z异常焦点的南北两边出现X的异常焦点,东西两边出现Y的异常焦点.中国地区的长期变化和长期加速度变化量小,分布相对均匀.     

Spherical harmonic analysis of the geomagnetic secular variation — A review of methods

Methods of producing spherical harmonic models of the secular variation of the geomagnetic field are reviewed and classified, more emphasis being given to modern methods. The relative merits of the different techniques are discussed and their relevance to possible procedures for updating the International Geomagnetic Reference Field (IGRF) are considered.