北京地磁台地磁场长期变化的初步研究

根据北京地磁台1987~2012年已正式出版的《地磁观测报告》资料,对北京地磁台地磁场的长期变化进行初步分析研究。系统地总结了北京地磁台地磁场长期变化的基本规律,这对进一步认识了解北京地磁台地磁场各要素的变化规律与特征,以及应用北京地磁台的资料有一定的意义。     

CM4模型数据与台站实测数据的对比研究

本文利用第四代地磁场综合模型(Comprehensive Model 4,CM4),计算了1982—2002年隆尧地磁台站的磁层源磁场及其感应场、电离层源磁场及其感应场的地磁北向分量X、东向分量Y、垂直分量Z,分析了各场源磁场随时间的变化特征。磁层源磁场及其感应场呈现出11年和27天的周期性变化,有些年的27天周期性变化显著,有些年则不太显著;电离层源磁场及其感应场具有明显的季节变化,不同年相同季节的变化形态一致但幅度不同;日变化分析显示,磁静日和磁扰日期间的模型数据与台站实测数据变化一致性较好,相关性较高。     

中国部分地磁台站年均值与IGRF模型一致性分析

利用中国部分地磁台站1990～2003年的年均值资料,研究了台站年均值与IGRF模型计算值的一致程度,结果表明：①我国地磁台站的长期变速度与IGRF模型的长期变速度有差异：总体来讲,我国台站磁偏角D和垂直强度Z的长期变速度低于IGRF模型的相应速度;水平强度H的长期变速度在1990～1995年间高于IGRF模型的相应速度,在1995～2000年间低于IGRF模型的相应速度;②台站年均值与IGRF模型值的差值曲线中,H和Z有明显的起伏,反映了地磁场长期变的非线性;③虽然有上述长期变上的差异,但对于同一个台站,各地磁要素年均值与IGRF模型值的差值的标准偏差均低于IGRF模型的误差水平,说明IGRF模型与台站年均值的一致性比较好;④对于同一地磁要素,不同台站的年均值与IGRF模型值的差值的平均值相差较大,反映出台站所在位置地壳磁异常的巨大差异。通过总结上述工作,文中还讨论了地磁台站保持长期可靠运行的重要性以及地磁台网历史观测资料抢救的紧迫性。     

国际地磁参考场在中国大陆地区的误差分析

IGRF（国际地磁参考场）是有关地球 主磁场与长期变化的模型，IGRF的误差主要来源于：忽略外源场、球谐级数的截断、台站分 布的不均匀、测量、忽略地壳磁异常场等. 分析我国大陆地区IGRF的误差，有利于我国地磁 研究 人员在工作中合理地应用IGRF资料. 如果不计磁异常与环境干扰都比较大的北京台，29个基 准台的IGRF的误差(均方根差)为146.9nT.     

北京国家地球观象台地磁场长期变化特征分析

利用北京国家地球观象台1957—2013年的地磁连续观测资料,对北京地磁场七个分量的均值和年变率进行分析,总结出地磁场七个要素不同的变化特征。此项工作对了解和应用北京地震台地磁的资料有一定的意义。     

Inversion of waveform from the data of six moderate strong earthquakes in Chinese mainland to seismic moment tensors and source mechanism

Based on Generalized Seismic Ray Theory (Helmberger, 1968), a new quickly linear inversion method from the data of seismic waveform to seismic moment tensor and source mechanism for domestic earthquake is studied in this paper. Six moderately strong earthquakes which occurred in Chinese mainland in the past few years are studied. The seismic source parameters of these earthquakes, seismic moment tensors, scalar seismic moments, fault plane solutions and source time functionsetc, are obtained. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 261–268, 1993.     

Solar cyclic variation in magnetic elements of Moscow observatory

The data of Moscow observatory for the 1946-2006 interval of observations are analyzed in order to detect long-term geomagnetic variations related to solar activity against a background of the secular variations in the geomagnetic field.     

Klimovskaya: A new geomagnetic observatory

In 2011 Geophysical Center RAS (GC RAS) began to deploy the Klimovskaya geomagnetic observatory in the south of Arkhangelsk region on the territory of the Institute of Physiology of Natural Adaptations, Ural Branch, Russian Academy of Sciences (IPNA UB RAS). The construction works followed the complex of preparatory measures taken in order to confirm that the observatory can be constructed on this territory and to select the optimal configuration of observatory structures. The observatory equipping stages are described in detail, the technological and design solutions are described, and the first results of the registered data quality control are presented. It has been concluded that Klimovskaya observatory can be included in INTERMAGNET network. The observatory can be used to monitor and estimate geomagnetic activity, because it is located at high latitudes and provides data in a timely manner to the scientific community via the web-site of the Russian–Ukrainian Geomagnetic Data Center. The role of ground observatories such as Klimovskaya remains critical for long-term observations of secular variation and for complex monitoring of the geomagnetic field in combination with low-orbiting satellite data.     

150 years of magnetic observatories: Recent researches on world data

A joint Discussion Meeting of the Royal Astronomical Society and the Royal Irish Academy, held on January 11th, 1991, commemorated the establishment of some early magnetic observatories, discussed recent research using global geomagnetic data and described the present status of magnetic observatories in the United Kingdom. The observatory and instruments at the Dublin magnetic observatory; the origins of the Greenwich magnetic observatory, and why it eventually had to be resited; and the history of the Munich magnetic observatory formed the historical part of the proceedings. Current research topics discussed were the geomagnetic secular variation and deep Earth structure and dynamics; fluid flow patterns near the top of the core; the origin of the annual variation of the geomagnetic field; results of an analysis of monthly means from some British observatories; a new theory of the geomagnetic daily variation; and the interactions between ionospheric science and geomagnetism. The present-day observatory scene was described in terms of the information that can be derived from the almost 40 year series of data from Hartland magnetic observatory; of the methods used to process data from the three UK magnetic observatories, which nowadays are operated automatically and remotely; and (a look into the future) of a new project, INTERMAGNET, which aims to make available, in near real time, data from the world-wide network of magnetic observatories.     

Variations of the geomagnetic field and the geomagnetic effects of three earthquakes ( M s>5.0) in Jiangsu Province, China

Since 1979 the repeated observations and experiments of geomagnetic total intensity and vertical component have been carried out for ten years in the geomagetic network which is located in Jiangsu Province, China. Three earthquakes aboveM _s 5.0 occurred during the decade, and some seismomagnetic effects were observed. The observation results show that the anomalies of the vertical geomagnetic component can’t be observed untill some months before the earthquake (M _s>5.0) in this area. In this paper it is suggested that a densely distributed network for continuous observation of geomagnetic vertical component may catch seismomagnetic anomalies and thus improve earthquake prediction in the light of the geomagnetic measurements of the mid — or — low latitude locations. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 80–87, 1991. This study is sponsored by the Chinese Joint Seismological Science Foundation.     

Geomagnetic daily variations around Huanghai earthquake

The geomagnetic daily variations of vertical component, which were recorded by geomagnetic array in Jiangsu Province, are investigated with the method of multichannel Wiener filtering. The results show that the daily standard errors between raw data and the actual output of the filter for the nearest stations away from epicenter are obviously higher than ordinary level before the Huanghai earthquake, especially three days before, then returned to normal after the earthquake. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 76–79, 1991. The project was supported by the Chinese Joint Seismological Science Foundation.     

磁通门磁力仪GM4定向方法的研究

仪器正确定向是保证仪器观测质量的一个重要环节。由于地磁场的长期变化,仪器需要定期重新定向。本文应用全国44个地磁台站2008—2012年观测数据,研究了各台站D分量的长期变化特征。结果表明,仪器定向位置和被测磁场位置产生较大偏离时,必须重新定向。同时首次提出影响定向精度的零场漂移S?0,并根据理论计算在红山地磁台实地开展测量,测量结果表明,零场漂移S0数值达到50.3 nT,超出D分量定向输出范围（磁静日时日变缓慢时间段为-50nT—+50nT）。     

Analytical comparison of geomagnetic total field between Sino-US stations

Using observational data of geomagnetic total intensity from 13 stations in the Beijing-Tianjin region, 3 stations in the western Yunnan region of China, and 6 stations in California of U. S. A., the daily variations and their spectra of geomagnetic total intensity were analyzed and compared. The results show that the morphology, the range and spectrum of daily variations in geomagnetic total intensity are basically the same within the local extent of 100–200 km and are different in the large extent of 500 km. The latitude factor of the daily variation range of geomagnetic total intensity is about 1–2 nT/degree within the latitude extent of 25°–40°. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 83–89, 1992. This work is supported by the State Seismological Bureau and the Chinese Joint Seismological Science Foundation, and U.S. Geological Survey.     

Fractals and magnetic storm

Fractal theory is applied in a quantitative analysis of geomagnetic storms. Fractal dimensions (D) of the attractor for storm data from the Beijing observatory (40.0°N, 116.2°E) using several time intervals are calculated. A maximum value of 1.4 has been obtained for a geomagnetic storm; on quite days the dimension is only slightly larger than 0.5. Data from two storms are analyzed here. Results show that a combination of both D and the magnetic index, k, can perhaps describe the degree of solar disturbance better than the single parameter k.     

Longitudinal variation in E- and F-region ionospheric trends

A novel technique is used to examine northern hemisphere midlatitude longitudinal variations in ionospheric long-term trends. Differences in hour-by-hour monthly median ionospheric parameters between equilatitudinal observatory pairs are analysed for long-term trends, thus eliminating at source the large solar cycle and geomagnetic variability that normally hinders ionospheric trend calculations. The results confirm the finding of Bremer [1998. Trends in the ionsopheric E- and F-regions over Europe. Annales Geophysicae 16, 698–996] that there are longitudinal variations in the F-region altitude trend across Europe, but suggest the influence of a stationary wave-like feature between 3°W and 104°E. Possible causes such as scaling errors, insufficient account of changes in ionisation underlying the F-region, varying gravity wave fluxes, and secular change in the geomagnetic field are ruled out. The data suggest that the longitudinal variation may reflect long-term changes in a large-scale stationary feature induced via non-migrating tides induced by latent heat release in the troposphere.Significant differences in the long-term trend of E-region peak plasma frequency between observatories were also found. These E-region differential trends varied with solar zenith angle reaching over 0.3 MHz per decade between Juliusruh and Moscow at midday in summer.     

北京地磁台的磁环境监测

对北京地磁台建台以来,台站周边环境随着北京城市化进程发生的变化做了较详细的描述.利用几次在台站地磁观测区范围内的地磁场梯度观测资料,分析了台站地磁观测场地磁场梯度的变化情况,并对现有地磁场梯度环境进行了评估.为北京地磁台及全国其他台站,在现有条件下的地磁观测工作提供了有益的参考.     

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.     

肇庆台数字化地磁观测资料震磁关系的分析研究

使用肇庆地磁台2003～2005年的高精度数字化地磁观测资料,采用地磁短周期转换函数、加卸载响应比等方法,系统地分析研究了肇庆地磁台周边地区在此期间的震磁异常对应关系。研究结果表明,在2004年9月17日阳江M_L 5．2级地震前,肇庆地磁台的地磁短周期转换函数A、B,加卸载响应比P(Z)均有比较明显的前兆异常。该异常具有中期异常特征,而对临震异常特征识别则不好区分和把握。     

"Double low-points" anomaly in daily variation of vertical component of geomagnetic field before the MS8.0 Wenchuan earthquake

The "double low-points" anomaly in daily variation of vertical geomagnetic component was observed on May 9, 2008 at 13 geomagnetic observatories belonging to the geomagnetic observatory network center of China Earthquake Administration. These observatories distribute roughly on three belts with the intersection in western Sichuan. On May 12, three days after the anomaly appearance, the great M_S8.0 Wenchuan earthquake occurred. The "double low-points" anomaly in daily variation of vertical geomagnetic component is an anomalous phenomenon of regional geomagnetism, which does exist objectively. The possible cause is the change of extrinsic eddy current system resulting in geomagnetic daily quiet variation (S_q), or the delay of several hours between the intrinsic and the extrinsic eddy current systems. The relationship between the "double low-points" anomaly of daily geomagnetic variation and the earthquake reveals that the former possibly reflects the accelerative alteration of earthquake gestation in the deep Earth.     

Research on geomagnetic tectonic characteristics of the crust in Haicheng seismic area

In this paper, the two metnods, rectangular spectrum (RS) and maximum entropy power spectrum (MES), have been used in calculating the geomagnetic structures of the crust in Haicheng and its adjacent areas and carrying out the geomagnetic stratification of the crust. The result of the research indicates that the crust can be devided into such three layers as nonmagnetic layer, magnetic layer and regressive magnetic layer from the top to the bottom. It is also found the distribution of the geomagnetic bottom interface (Curie surface) is consistent with the lower interface of the upper crust and the top interface of the middle crust of the velocity structure of the crust. It is very interesting that the Haicheng earthquake of Feb. 4, 1975,M 7.3 occurred at the depth gradient belt of the Curie isotherm surface. So, to research on the geomagnetic layers and the distribution characteristics of the Curie isotherm surface is meaningful in judging potential seismic foci. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 448–454, 1993. The data of velocity and electricity materials used in this paper are as reference from the related materials of the maps and directions etc. of Donggou-Haicheng-Dong Ujimqin Qi Geoscience Transect by Prof. Zao-Xun LU, Huai-Kuan XIA and others.