张北地震前地磁空间相关异常特征

应用地磁空间相关方法对华北地区１９９６年１月至１９９８年１月地磁核旋定点（北京时２１ｈ）观测数据的分析研究表明，１９９８年１月１０日张北ＭＳ６．２地震和１９９６年５月３日内蒙古包头ＭＳ６．４地震前存在地磁空间相关低值异常。

泾县及周边地磁空间地震磁效应分析研究

传统基于小波变换的地震磁效应分析方法,没有考虑空间上的相关性,分析结果误差较大。提出新的地磁空间地震磁效应分析方法,采用小波变换分析法获取地震磁效应波动的时间信息。时间序列随机时刻的频率以及频率波动特性,采用地震磁效应波动的空间线性相关性分析方法,对基本背景场中时间序列随机时刻频率的波动产生的影响进行彻底清除,使地震磁效应波动的异常状态与地震的关系更加突出,实现地震磁效应波动的空间线性相关性分析。结果表明:以泾县及周边地域地震为例,所提方法具有较低的地磁空间地震磁效应分析误差,其稳定性以及信息含量评分是95.7分和96.4分,具有较高的分析性能。

地磁学发展史的启示

地磁学诞生于指南针的发明和测向的应用,它的发展从一开始就与实际应用紧密结合,因此,鲜明的实用性色彩是地磁学这门古老学科与生俱来的特点,正是这一特点。使地磁学有着广泛而实在的社会需求,因而也获得了强劲而持续的发展动力。另一方面,地磁学的基本理论(如地磁场起源、电磁波传播、磁层与电离层的形成以及日地相互作用等)深深植根于物理学、化学和数学,这就使得地磁学得以与数理科学同步发展。此外,地磁学是以磁场测量为基础的实验性学科,所以,它又与技术进步息息相关,新仪器的发明、计算机的发展和空间探测无不有力地推动着地磁学的发展。

强烈地磁扰动的危害

本文给出了强烈地磁扰动可能对空间和地面技术系统、人类的生产和生活造成的危害,其中包括地磁扰动的直接危害和由于地磁感应电流造成的危害及伴随的其他空间环境扰动所造成的危害。

1900～2000年地磁场及长期变化的空间功率谱分析

根据第 8代国际地磁参考场模型 ,计算并分析了 190 0～ 2 0 0 0年地球主磁场及长期变化的空间功率谱 ,并将长期变化谱分解为稳定和漂移谱、漂移谱又分解为经向漂移和纬向漂移谱分别进行分析 .结果表明190 0～ 2 0 0 0年主磁场的空间功率谱得出的等效磁源深度随时间变化 ,非偶极子场的等效磁源深度位于核幔边界附近 ,用n =1,2两阶谐波的拟合直线得到的等效磁源位于地球内核边缘 ,而且 190 0年以来离地心向外增大 .长期变化中 ,经度方向的漂移谱起主要作用 ,漂移谱有 30a的周期规律 ,而稳定谱存在 6 0a的周期变化特征 .

Three-dimensional conjugate gradient inversion of magnetotelluric sounding data

Based on the analysis of the conjugate gradient algorithm, we implement a threedimensional （3D） conjugate gradient inversion algorithm with magnetotelluric impedance data. During the inversion process, the 3D conjugate gradient inversion algorithm doesn＇ t need to compute and store the Jacobian matrix but directly updates the model from the computation of the Jacobian matrix. Requiring only one forward and four pseudo-forward modeling applications per frequency to produce the model update at each iteration, this algorithm efficiently reduces the computation of the inversion. From a trial inversion with synthetic magnetotelluric data, the validity and stability of the 3D conjugate gradient inversion algorithm is verified.

2D joint inversion of CSAMT and magnetic data based on cross-gradient theory

A two-dimensional forward and backward algorithm for the controlled-source audio-frequency magnetotelluric （CSAMT） method is developed to invert data in the entire region （near, transition, and far） and deal with the effects of artificial sources. First, a regularization factor is introduced in the 2D magnetic inversion, and the magnetic susceptibility is updated in logarithmic form so that the inversion magnetic susceptibility is always positive. Second, the joint inversion of the CSAMT and magnetic methods is completed with the introduction of the cross gradient. By searching for the weight of the cross-gradient term in the objective function, the mutual influence between two different physical properties at different locations are avoided. Model tests show that the joint inversion based on cross-gradient theory offers better results than the single-method inversion. The 2D forward and inverse algorithm for CSAMT with source can effectively deal with artificial sources and ensures the reliability of the final joint inversion algorithm.

Influence and hazard of disastrous space weather on power grid in China

Based on the measured data of geomagnetically induced currents （GIC） in Guangdong Ling＇ ao 500 kV power networks during several magnetic storms at the peak years of 23rd Solar Cycle, the GIC calculation results of 750 kV planning power grid in Shartxi, Gansu, Qinghai and Ningxia, the structure and characteristics of power networks from 500 kV to 1 000 kV, and super magnetic storm in 1859 are analyzed in this paper. Through the analysis, the possible impacts of extreme space weather on the future ultra-high voltage （UHV） grid, the security of large-scale power system in China are expounded, and the research suggestions coping with the strong solar storms are proposed.

井下地磁定位的区域适配性研究与分析

井下地磁空间分布特征的适配性评价是井下地磁定位导航的基础.文中针对井下地磁区域适配性问题,在统计分析井下地磁空间分布特征的基础上,增加了变异系数和粗糙方差比作为带状小区域特征指标.并提出了一种基于回归分析多因子联合评价方法,通过多元回归分析确定了参与评价的特征指标,采用离差最大化和Jaynes最大熵原理确定评价因子的权值,改进了传统的决策属性判别过程的特征选取方式,降低了评价过程的主观性.试验选取了矿井以及人防工程的25个实验区域进行地磁数据采集,进行了传统阈值适配评价和基于回归分析多因子联合评价的对比实验及验证.实验结果表明,基于多元线性回归的多因子联合评价结果比单一特征参数评价结果好,达到了80%的相符率,在一定程度可以弥补单因子评价的主观影响.

Magnetohydrodynamics (MHD) numerical simulations on the interaction of the solar wind with the magnetosphere: A review

The magnetosphere is the outermost layer of the geospace, and the interaction of the solar wind with the magnetosphere is the key element of the space weather cause-and-effect chain process from the Sun to Earth, which is one of the most challenging scientific problems in the geospace weather study. The nonlinearity, multiple component, and time-dependent nature of the geospace make it very difficult to describe the physical process in geospace using traditional analytic analysis approach. Numerical simulations, a new research tool developed in recent decades, have a deep impact on the theory and application of the geospace. MHD simulations started at the end of the 1970s, and the initial study was limited to two-dimensional (2D) cases. Due to the intrinsic three-dimensional (3D) characteristics of the geospace, 3D MHD simulations emerged in the 1980s, in an attempt to model the large-scale structures and fundamental physical processes in the magnetosphere. They started to combine with the space exploration missions in the 1990s and make comparisons with observations. Physics-based space weather forecast models started to be developed in the 21st century. Currently only a few space-power countries such as USA and Japan have developed 3D magnetospheric MHD models. With the rapid advance of space science in China, we have developed a new global MHD model, namely PPMLR-MHD, which has high order spatial accuracy and low numerical dissipation. In this review, we will briefly introduce the global 3D MHD modeling, especially the PPMLR-MHD code, and summarize our recent work based on the PPMLR-MHD model, with an emphasis on the interaction of interplanetary shocks with the magnetosphere, large-scale current systems, reconnection voltage and transpolar potential drop, and Kelvin-Helmholtz (K-H) instability at the magnetopause.

Comparison between the ring current energy injection and decay under southward and northward IMF Bz conditions during geomagnetic storms

The geomagnetic storm is one of the most important geomagnetic disturbance phenomena in the geospace.Many studies assume that input of solar wind energy into the Earth's ring current only occurs when IMF Bz in GSM coordinates is southward;the ring current energy injection and decay under northward IMF Bz are not well understood and still need further investigation.In this paper,by using the large amount of data from the year 1964 to 2010,we use the empirical phase space analysis method to study the ring current energy injection and decay under northward IMF Bz and compare the results with those under southward IMF Bz condition.We have found that the largest injection Q under northward IMF Bz condition is only 7% of the largest injection under southward IMF Bz,implying that there is a very limit energy injected into the ring current region when IMF Bz is northward.The decay time decreases as VBz increases and shows a good linear trend for southward IMF Bz;while for the northward IMF Bz,there is not a clear relation between τ varies and VBz.Having taken τ as a function of injection Q instead of VBz,we have obtained the empirical relation of τ with Q for northward and southward IMF Bz conditions:the two categories are further combined together and the empirical relation τ= e(2.6 0.039 Q) is derived.Further,the pressure-corrected Dst formula Dst=Dst b P+c is derived for both southward and northward IMF Bz conditions,where the coefficients b and c are 6.9/10.4 and 10.0/15.2 when IMF Bz is southward and northward respectively.The statistical results on between the different geomagnetic indices(Dst,Kp,AE) and IMF Bz are also obtained.

The state-of-the-art of the China Seismo-Electromagnetic Satellite mission

The China Seismo-Electromagnetic Satellite(CSES) mission was proposed in 2003 and approved in 2013 after ten years' scientific and engineering demonstrations. To meet the requirement of scientific objectives, the satellite is designed to be in a sunsynchronous orbit with an altitude of 507 km and descending node time of 14:00 LT. The CSES satellite carries 8 instruments,including search-coil magnetometer(SCM), electric field detector(EFD), high precision magnetometer(HPM), GNSS occultation receiver(GOR), plasma analyzer package(PAP), langmuir probe(LAP), high energetic particle package(HEPP) and detector(HEPD), and tri-band beacon(TBB), among which HEPD is provided by Italian Space Agency. The CSES satellite was launched successfully on February 2, 2018, and is planned to operate for 5 years. The CSES mission is the first satellite in China to measure geophysical fields, which will have a lot of application prospects in the study of seismology, geophysics, space sciences, and so on.

Spatial Distribution of Magnetic Properties and Selected Heavy Metals in Calcareous Soils as Affected by Land Use in the Isfahan Region,Central Iran

Anthropogenic activities have caused the accumulation of heavy metals in the soil environment. Pollution of the soils significantly reduces environmental quality and affects human health. In many recent studies, magnetic susceptibility ts have been used for pollution monitoring. The objective of this research was to determine the spatial variability of magnetic properties and selected heavy metals and the effect of land use on their variability in the surface soils of the Isfahan region, Central Iran. A total of 158 composite surface （0-5 cm） samples of calcareous soils were collected from an area of about 700 km2, located along a cross-border transect from Isfahan City to a steel plant, covering urban, industrial, agricultural, and uncultivated land uses. Concentrations of copper （Cu）, zinc （Zn）, lead （Pb）, manganese （Mn）, iron （Fe）, nickel （Ni）, chromium （Cr）, and cobalt （Co） and magnetic parameters, magnetic susceptibility at low frequency （xlf）, natural remanent magnetization （NRM）, saturation isothermal remanent magnetization （SIRM）, and isothermal remanent magnetization at the field of 100 mT （IRM100mT） and the backfield of 100 mT （IRM-100mT）, were measured in all the soil samples. Results showed that magnetic susceptibility in the urban and industrial land topsoils （0-5 cm） samples was significantly higher than that in the agricultural and uncultivated land soils in the study area. Concentrations of Cu, Zn, Pb, Mn, and Fe were positively correlated with magnetic properties （xlf, IRM100mT, SIRM, IRM-100mT, and NRM）, which could be attributed to their inputs from traffic emissions and industrial activities at the study sites. Ni and Cr concentrations showed significant negative correlations with magnetic properties. No significant correlation was found between Co concentration and magnetic parameters. The Tomlinson pollution load index （PLI） showed significant correlation with the magnetic properties （xlf, IRM100mT, SIRM, IRM-100mT, and NRM）. The spatial distribution of the selected heavy metals and xlf in the study area suggested that activities at the urban and industrial land sites caused greater pollution as compared to that at the study sites of other land uses. The concentrations of Cu and Zn seemed to have been affected by anthropogenic sources, whereas Ni, Cr, and Co were mainly controlled by natural sources in the study area. Moreover, the concentrations of soil Pb and Fe in the study area could be affected by both lithologic and anthropogenic sources. The magnetic parameters appeared to be a proxy measure for the degree of heavy metal contamination and could be a potential method for the detection and mapping of contaminated soils.

Improved method to derive equivalent current systems from global MHD simulations

Derivation of equivalent current systems(ECS)from a global magnetospheric magnetohydrodynamics(MHD)model is very useful in studying magnetosphere-ionosphere coupling,ground induction effects,and space weather forecast.In this study we introduce an improved method to derive the ECS from a global MHD model,which takes account of the obliqueness of the magnetic field lines.By comparing the ECS derived from this improved method and the previous method,we find that the main characteristics of the ECS derived from the two methods are generally consistent with each other,but the eastward-westward component of the geomagnetic perturbation calculated from the ECS derived from the improved method is much stronger than that from the previous method.We then compare the geomagnetic perturbation as a function of the interplanetary magnetic field(IMF)clock angle calculated from the ECS derived from both methods with the observations.The comparison indicates that the improved method can improve the performance of the simulation.Furthermore,it is found that the incomplete counterbalance of the geomagnetic effect produced by the ionospheric poloidal current and field-aligned current(FAC)contributes to most of the eastward-westward component of geomagnetic perturbation.