Prediction of geomagnetic storms from solar wind data with the use of a neural network

An artificial feed-forward neural network with one hidden layer and error back-propagation learning is used to predict the geomagnetic activity index (D_st) one hour in advance. The B_z-component and _Bz, the density, and the velocity of the solar wind are used as input to the network. The network is trained on data covering a total of 8700 h, extracted from the 25-year period from 1963 to 1987, taken from the NSSDC data base. The performance of the network is examined with test data, not included in the training set, which covers 386 h and includes four different storms. Whilst the network predicts the initial and main phase well, the recovery phase is not modelled correctly, implying that a single hidden layer error back-propagation network is not enough, if the measured D_st is not available instantaneously. The performance of the network is independent of whether the raw parameters are used, or the electric field and square root of the dynamical pressure.     

Predicting geomagnetic storms from solar-wind data using time-delay neural networks

We have used time-delay feed-forward neural networks to compute the geomagnetic-activity index D_st one hour ahead from a temporal sequence of solar-wind data. The input data include solar-wind density n, velocity V and the southward component B_z of the interplanetary magnetic field. D_st is not included in the input data. The networks implement an explicit functional relationship between the solar wind and the geomagnetic disturbance, including both direct and time-delayed non-linear relations. In this study we especially consider the influence of varying the temporal size of the input-data sequence. The networks are trained on data covering 6600 h, and tested on data covering 2100 h. It is found that the initial and main phases of geomagnetic storms are well predicted, almost independent of the length of the input-data sequence. However, to predict the recovery phase, we have to use up to 20 h of solar-wind input data. The recovery phase is mainly governed by the ring-current loss processes, and is very much dependent on the ring-current history, and thus also the solar-wind history. With due consideration of the time history when optimizing the networks, we can reproduce 84% of the D_st variance.     

Solar origin of geomagnetic storms and prediction of storms with the use of neural networks

This review deals with how the changes of the large-scale solar magnetic fields are related to the occurrence of solar phenomena, which are associated with geomagnetic storms. The review also describes how artificial neural networks have been used to forecast geomagnetic storms either from daily solar input data or from hourly solar wind data. With solar data as input predictions 1–3 days or a month in advance are possible, while using solar wind data as input predictions about an hour in advance are possible. The predictions one hour ahead of the geomagnetic storm indexD _st from only solar wind input data have reached such high accuracy, that they are of practical use in combination with real-time solar wind observations at L1. However, the predictions days and a month ahead need to be much improved in order to be of real practical use.     

高邮-宝应4.9级地震地磁谐波振幅比异常特征初步分析

针对高邮-宝应4.9级地震发生前后附近地区未发生其它中等以上地震、地震事件孤立及周边地磁台站分布较密有利于研究地震地磁异常时空特征的特点,较为系统地分析总结了该地震发生前后地磁谐波振幅比的变化特征,研究结果进一步验证了目前对地磁谐波振幅比异常特征的认识,即地磁谐波振幅比异常特征表现出与地电阻率类似的下降-转折-恢复上升的异常变化过程,地震一般发生在异常转折或恢复上升过程中,距震中较近的台站会出现不同步现象——南北向与东西向的不同步以及长短周期的不同步。     

Non-linear predictions ofAp by activity class and numerical value

Two neural network algorithms are applied to the short-term,1 to 3 days, prediction of theAp geomagnetic index. A multi-layer, back-propagation (MBP) network is used to implement a self-prediction filter forAp and this provides a forecast of the numerical value of the index. A probabilistic neural network (PNN) is used to estimate the probability distribution of theAp index, in six activity classes, and to provide a forecast of the single most likely activity class for each day. BothAp and an index of solar activity, based on the daily reports issued by the Space Environment Services Centre (Boulder), are input to the probabilistic net. It is found that the numerical forecasts of the MBP filter are most accurate at low, non-storm, levels of activity. This non-linear method provides quantitatively better estimates of activity than are produced by an existing linear prediction filter, particularly with increasing forward forecasting lag. At high levels of the solar activity index the PNN is found to anticipate storm classAp with around 60% accuracy in 1992 and 1993. Some details of the algorithms and implementation issues are described. It is concluded that interplanetary field and solar wind data will be significant components of any of the possible future developments which are discussed.     

Secular variations ing 1 0 component of geomagnetic field and its origin

The secular variations (SV) ing ₁ ⁰ of geomagnetic field, caused by the interaction between the geomagnetic field and the radial fluid-flow of the outer-core, are discussed with both statistical and analytic methods. When the value ofg ₁ ⁰ s ₂ ⁰ is relatively high compared with other terms, SV ing ₁ ⁰ is characterized by exponential change. When the effect of non-dipole field is notable, SV ing ₁ ⁰ shows complex features. Especially when the value of g ₁ ⁰ is close to zero, SV ing ₁ ⁰ is completely determined by the random process of non-dipole fields. Project supported by the National Natural Science Foundation of China (Grant No. 49429405) and by the Chinese Academy of Sciences.     

Variations in the geomagnetic cutoff rigidity of cosmic rays at individual points of the Asian region during the extreme events of 2003

The variations in the geomagnetic cutoff rigidity in Irkutsk, Alma-Ata, and Beijing in October–November 2003 were calculated using ground-based measurements of cosmic ray intensity from the worldwide network of stations and GOES spacecraft. The calculated variations in geomagnetic cutoff rigidity are presented together with D _st variations of the geomagnetic field. The obtained results are compared to calculations performed using the Tsyganenko model of the magnetosphere.     

2018年云南通海MS5.0和墨江MS5.9地震前地磁垂直强度极化异常时空特征研究

利用云南11个地磁台站的秒采样观测数据,计算和分析了地磁垂直强度极化值Y_zh在2019年8月13日、14日通海M_S5.0地震前及2019年9月8日墨江M_S5.9地震前的时空变化特征。研究表明,地磁台站Y_zh值的幅度在震前会出现同步增强现象。而与以往的极化震例研究相比,Y_zh值的高值异常在震前出现时间要更早些,可能会在震前2~5个月出现,距发震时间越近,产生的异常幅值可能越大,异常持续时间也越长。同时,研究还发现2次地震主要发生在异常空间等值线的高值区内,尤其在零值阈值线附近,这可能对今后发震地点的预测有一定的指示意义。对比异常产生时段内的D_st指数,认为该高值异常并非由空间电流体系所引起。     

Spatial Correlation Anomalies of the Diurnal Variation of the Geomagnetic Vertical Component before the Yingjiang MS6.1 and Ludian MS6.5 Earthquakes

Significant anomalies were observed at the geomagnetic stations in the southwest region of China before the Yingjiang M_S6.1 earthquake and the Ludian M_S6.5 earthquake in 2014. We processed the geomagnetic vertical component diurnal variation data by the spatial correlation method. The results show that during the period from April 1 to May 20, 2014,there existed quasi-synchronous decrease changes in the coefficient curves between the five geomagnetic stations of Guiyang,Hechi,Nanshan,Muli,Yongning and Xinyi and Hongshan stations.Furthermore,there was a high gradient zone in the normalized correlation coefficient contour map with background values removed. The epicenters of the Yingjiang M_S6.1 earthquake and the Ludian M_S6.5 earthquake are located in the gradient zone or near the gradient zone.     

汶川8.0级地震前地磁日变化异常综合分析

运用地磁低点位移、地磁加卸载响应比和地磁Z分量日变幅逐日比3种地磁分析方法,分析了2008年5月12日汶川8.0级地震前的地磁前兆异常现象。研究发现,运用上述3种方法,汶川地震前出现多次异常,地震发生在异常预测线集中交汇区域。综合分析结果显示,地磁多方法综合分析可以有效提升地震预测的精确性。文章还讨论了地磁日变化畸变异常机理问题。     

Relationship between variations in the characteristics of the high-latitude ionosphere and magnetic <Emphasis Type="Italic">PC</Emphasis> indices

It is shown in a joint analysis of ionospheric vertical sounding data at the arctic Heiss Island and antarctic Vostok stations and the geomagnetic PC index, which characterizes the geoefficient component of the interplanetary magnetic field, that, during a disturbed geomagnetic period when PC > 2 in years of solar activity (SA) maxima in the winter season, positive phases of ionospheric disturbances are predominantly observed. In the nighttime hours, an increase in the critical foF2 frequencies by a factor of 2–3 can occur. In a disturbed geomagnetic period at the PC > 1.5 level in the summer season, negative phases of ionospheric disturbances are mainly observed. In years of maximum and moderate SA, the decrease in foF2, as compared to their median values, happens at night (∼30%). In years of low SA, the decrease value is much lower. At a substantial decrease in the PC index level, in the region of the geomagnetic pole at the Vostok station, in some cases, a substantial increase in the electron density level in the F region occurs with a delay of 0.5 h. At the same time, a significant correlation (r = −0.57) is observed between variations in the PC index and foF2.     

On the geomagnetic and ionospheric responses to an intense storm associated with weak IMF Bz and high solar wind dynamic pressure

A study of the geomagnetic storm of July 13–14, 1982, and its ionospheric response is presented using the low-latitude magnetic index, Dst, and interpreted using solar wind interplanetary data: proton number density, solar wind flow speed, interplanetary magnetic field southward component B _Z , and solar wind dynamic pressure. The F2 region structure response to the geomagnetic storm was studied using foF2 data obtained during the storm from a network of various ionosonde stations. Our results appear to show simultaneous abrupt depletion of foF2 that occurred at all latitudes in both the East Asian and African/European longitudinal zone during the period: 18:00–19:00 UT on July 13 and is as result of an abrupt increase in the dynamic pressure between 16:00 and 17:00 UT. The dynamic pressure increased from 3.21 to 28.07 nPa within an hour. The aforementioned abrupt depletion of foF2 simultaneously resulted in an intense negative storm with peak depletion of foF2 at about 19:00 at all the stations in the East Asian longitudinal zone. In the African/European longitudinal zone, this simultaneous abrupt depletion of foF2 resulted in intense negative storm that occurred simultaneously at the low latitude stations with peak depletion at about 20:00 UT on July 13, while the resulting negative storm at the mid latitude stations recorded peak depletion of foF2 simultaneously at about 2:00 UT on July 14. The present results indicate that most of the stations in the three longitudinal zones showed some level of simultaneity in the depletion of foF2 between 18:00 UT on July 13 and 2:00 UT on July 14. The depletion of foF2 during the main phase of the storm was especially strongly dependent on the solar wind dynamic pressure.     

An evaluation method of hydrocarbon generating potential of highly mature and over-mature marine carbonate

How to restore the residual organic carbon and residual hydrocarbon-generating potential is discussed based on the hydrocarbon degradability of source rock. The results indicate there is linear function relationship between the restoring coefficient of residual organic carbon (K_c) and the vitrinite reflectance (R _o%) of various kinds of source rock, but the relationship is secondary functional between the restoring coefficient of residual hydrocarbon-generating potential (K_s) and the vitrinite reflectance (R _o%). It is pointed out thatKc = (1 -Dresidual)/(1 -D _primary),Ks= Kc (D _primary/D _residual). The restoration of residual organic carbon and hydrocarbon-generating potential of the Cambrian and Ordovician highly mature marine carbonate in the Tarim Basin and North China region shows that the lower limit value of hydrocarbon generating potential and the organic matter abundance of carbonate source rock are basically the same as that of clastic rock. The technical difficulty in hydrocarbon generating evaluation of highly mature and overmature carbonate is solved.     

2017年精河MS6.6地震前地磁异常特征分析

2017年8月9精河发生M_S6.6地震,距震中300km范围内的温泉台、克拉玛依台、乌鲁木齐台捕捉到此次地震前的地磁异常信息,本文对此进行了分析和总结,结论如下：①地磁谐波振幅比反应了观测点深部电阻率变化,2016年呼图壁M_S6.2、此次精河M_S6.6地震均发生在克拉玛依台地磁谐波振幅比异常下降之后的转折和恢复阶段;②震前83天、21天沿北天山断裂带分布的地磁台站逐日比和加卸载响应比均成组出现超限的高值,且异常高值的空间分布与震中位置有一定关联;③全国大陆地磁台站震前34天出现低点位移突变分界线,且异常集中于震中附近。     

Studying ionospheric responses to magnetic storms depending on the local time of the storm main phase onset

A morphological analysis of vertical sounding data obtained in Irkutsk from 2003 to 2008 has been performed. The AE index was used to determine the geomagnetic activity level, and the storm main phase onset was registered based on the D _st index. The ionospheric response to a magnetic storm was estimated based on the relative deviation of the critical frequency and altitude of the ionospheric F2 region from the median values. Superstrong magnetic storms and storms without positive initial phases were not considered when the data were selected. We found that positive ionospheric disturbances, which were accompanied by an increase in the F2 region maximum altitude, predominated between the storm initial phase and main phases during all considered magnetic storms. Between these storm phases, negative disturbances were only registered at night. Predominance of positive ionospheric disturbances over negative ones can be related to the selection of storms for studies.     

Self-diffusion studies of pore fluids in unconsolidated sediments by PFG NMR

The self-diffusion of water and hexadecane in medium and coarse sands from glacial sand deposits in central Germany were investigated by pulsed field gradient nuclear magnetic resonance (PFG NMR). Due to the restriction of the diffusion path at the pore/grain interface, the measured apparent self-diffusion coefficients (D(Δ)) in the pore space depend on the observation time (Δ) in the PFG NMR experiment. Although the bulk self-diffusion coefficients of water and hexadecane differ by about one order of magnitude, the apparent self-diffusion coefficients in the pore space obey the same characteristic time-behaviour, which depends only on geometrical properties of the pore system. Using the “short-time diffusion” model, surface-to-volume (S/V) ratios and inherent self-diffusion coefficients (D₀) of the pore fluids were extracted from these diffusion measurements. The S/V ratios obtained are independent of the pore fluid used and agree with known geometrical properties of the sand grains. Moreover, the D₀ values are consistent with the corresponding bulk self-diffusion coefficients measured separately. In contrast to these results of PFG NMR, simultaneous investigations of longitudinal (T₁) nuclear magnetic relaxation reveal that the relaxation time of the pore fluid is a less suitable parameter for a quantitative estimation of geometrical properties of the pore/grain interface in these unconsolidated sediments since it depends on chemical properties of the fluid/grain interface.     

Harmonization check of M w within the central, northern, and northwestern European earthquake catalogue (CENEC)

Large data sets covering large areas and time spans and composed of many different independent sources raise the question of the obtained degree of harmonization. The present study is an analysis of the harmonization with respect to the moment magnitude M _w within the earthquake catalogue for central, northern, and northwestern Europe (CENEC). The CENEC earthquake catalogue (Grünthal et al., J Seismol, 2009) contains parameters for over 8,000 events in the time period 1000–2004 with magnitude M _w ≥ 3.5. Only about 2% of the data used for CENEC have original M _w magnitudes derived directly from digital data. Some of the local catalogues and data files providing data give M _w, but calculated by the respective agency from other magnitude measures or intensity. About 60% of the local data give strength measures other than M _w, and these have to be transformed by us using available formulae or new regressions based on original M _w data. Although all events are thus unified to M _w magnitude, inhomogeneity in the M _w obtained from over 40 local catalogues and data files and 50 special studies is inevitable. Two different approaches have been followed to investigate the compatibility of the different M _w sets throughout CENEC. The first harmonization check is performed using M _w from moment tensor solutions from SMTS and Pondrelli et al. (Phys Earth Planet Inter 130:71–101, 2002; Phys Earth Planet Inter 164:90–112, 2007). The method to derive the SMTS is described, e.g., by Braunmiller et al. (Tectonophysics 356:5–22, 2002) and Bernardi et al. (Geophys J Int 157:703–716, 2004), and the data are available in greater extent since 1997. One check is made against the M _w given in national catalogues and another against the M _w derived by applying different empirical relations developed for CENEC. The second harmonization check concerns the vast majority of data in CENEC related to earthquakes prior to 1997 or where no moment tensor based M _w exists. In this case, an empirical relation for the M _w dependence on epicentral intensity (I ₀) and focal depth (h) was derived for 41 master events, i.e., earthquakes, located all over central Europe, with high-quality data. To include also the data lacking h, the corresponding depth-independent relation for these 41 events was also derived. These equations are compared with the different sets of data from which CENEC has been composed, and the goodness of fit is demonstrated for each set. The vast majority of the events are very well or reasonably consistent with the respective relation so that the data can be said to be harmonized with respect to M _w, but there are exceptions, which are discussed in detail.     

2017年8月8日九寨沟MS7.0地震前成都台地磁谐波振幅比异常分析

2017年8月8日四川省九寨沟县发生M_S7.0地震,成都地震基准台距此次地震震中约255km,震前该台地磁谐波振幅比出现趋势性异常。对成都台GM4磁通门磁力仪秒数据进行谐波振幅比计算,结果显示,谐波振幅比在九寨沟M_S7.0地震前表现出下降—转折—恢复上升的异常变化形态,地震发生在异常恢复期,同时,异常表现出由长周期向短周期迁移、SN向与EW向变化不同步的特征,芦山M_S7.0地震前成都台地磁谐波振幅比亦呈现了相似的异常变化特征。     

青海祁连MS5.2地震微震检测与目录完备性研究

利用模板匹配方法对2015年11月23日青海省祁连县M_S5.2地震进行遗漏地震检测研究,由于主震后短时间内目录中遗漏事件较多,故对主震后1天的连续波形进行检测。主震后1天内青海测震台网记录到的余震个数(包括单台)共62个,选取主震后M_L1.0以上余震30个作为模板事件,通过匹配滤波的方式扫描出遗漏地震31个,约为台网目录给出的0.5倍。基于包络差峰值振幅与震级的线性关系估测检测事件的震级参数,最后将检测后的余震目录与台网余震目录在主震后1天内的最小完备震级进行对比分析,结果发现检测后最小完备震级从M_L1.2降到了M_L0.7,得到青海测震台网在祁连地区最小完整性震级为M_L0.7。     

2013年岷县—漳县6.6级地震前地磁日变化异常及机理分析

利用空间相关法对2013年岷县—漳县6.6级地震前后151个台站地磁垂直分量日变化进行分析,结果显示:(1)2013年7月3日、4日在震中附近分别出现16和17个台站的地磁Z分量日变化明显反相位异常,具有明显的分界线。(2)利用S变换方法对分界线两侧的天水和兰州台的Z分量日变化进行分频率相关系数计算,发现7月3日、4日的地磁Z分量的日变化均在6 h左右的周期出现负相关变化。其他时段未出现类似变化,认为岷县—漳县6.6级地震前地磁Z分量日变化异常产生的反相位异常主要在6 h左右。此外,还对异常产生的机理进行了解释。