Archaeomagnetic study of ceramics from the El Molon archaeological monument (Spain

Data on the geomagnetic field intensity in the first millennium BC and the 8th–10th centuries AD are obtained from the study of materials from the El Molon archaeological monument (Spain). A 75-yr averaged curve of the variation in the geomagnetic field intensity in the area of the zero meridian over the last three millennia is constructed from a set of new and previously obtained data on the geomagnetic intensity variations in Spain and France. The field intensity smoothly decreases in the time interval studied, and variations a few centuries long are superimposed on this trend. Unlike the present-day relationship, the average level of the geomagnetic field intensity in Spain in the first millennium BC was higher than in the Caucasus.     

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.     

Archaeomagnetic study of ceramics from the Neolithic Los Castillejos multilayer monument (Montefrio,Spain)

The geomagnetic intensity variation from the middle of the 4th millennium BC to the beginning of the 2nd millennium BC is reconstructed from the archaeomagnetic study of ceramic material taken from 24 layers of the Los Castillejos monument (Montefrio, Spain). The general patterns of the geomagnetic intensity variation reconstructed by studying materials from the Cendres Cave and Los Castillejos monuments (Spain) are similar. The intensity level is revised in the time interval including the minimum of the “fundamental” oscillation of the geomagnetic field; the characteristics of geomagnetic intensity variations whose superposition can provide the intensity variation observed in the study time interval are determined. Constraints on the climate humidity variation over the settlement lifetime are obtained from heating-induced variations in the magnetic susceptibility of the ceramics.     

Variations in geomagnetic intensity and temperature in the second Millennium B.C. in Spain

The Bronze ceramics of the Baeza archeological monument in Spain is studied by archaeomagnetic methods. In the 19th and 18th centuries B.C, the intensity of the geomagnetic field varied from 40 to 60 mkT. The variations are smooth; they attained their maximum in the 16th to 15th centuries B.C. The obtained data on the variations in the geomagnetic intensity perfectly agree with the results of previous investigations for the ceramics from the Bronze Age multilayered archeological monuments Azuer and Ubeda. The temperature in the region of the Baeza monument is estimated in the interval from the 18th to the 13th centuries B.C. It experiences wave-like variation, ranging from ??15 to 23°C and attains its maximum in the 16th century B.C.     

Geomagnetic evolution: 400 years of change on planet Earth

Spherical harmonic coefficients of the geomagnetic field, calculated from historical observations of declination, inclination and intensity, and from archaeomagnetic inclination results, have been used to produce a film of geomagnetic change since 1600 A.D. The non-dipole geomagnetic field is found to be constantly changing: no fixed or standing non-dipole features are observed. Non-dipole foci are seen to have lifetimes of a few hundred years. The westward drift, which was an important feature of the 18th and early 19th century geomagnetic field, was less pronounced in the 17th century. The growth, evolution, decay and replacement of non-dipole foci, but not their movement are found to have been the major features producing century-long secular directional magnetic variation. Most of the low degree and order spherical harmonic coefficients have changed significantly over the last few hundred years. In particular the change in sign of the axisymmetric quadrupole around 1837 A.D. is noted. Sustained, century-long, intensity changes, however, appear to have been dominated by variations in the intensity of the centred dipole, rather than by non-dipole field fluctuations.     

Variations of the main geomagnetic field intensity in the region of the Taman Peninsula during the last 13 centuries

The archaeomagnetic studies of ceramics from the Hermonassa multilayer archaeological monument in the Taman Peninsula provided the data on the intensity of the main geomagnetic field in the past. The data for the interval from VIII to XX centuries A.D. demonstrate a well pronounced decreasing trend in the geomagnetic field intensity during this time. Three stages, each lasting for a few centuries, are distinguished in the variations of the centennial average field which slightly varies within each stage and generally decreases from 70 to ~45 μT during the entire period from VIII to XX centuries A.D. The variations of the geomagnetic field in the interval from XII to XVII centuries A.D. have a form of quasi-harmonic oscillations with a characteristic time of about 300 years.     

Geomagnetic Field Intensity during the Neolith in the Central East European Plain

The conducted archeomagnetic studies resulted in data on variations in the geomagnetic field intensity in the central East European Plain (Sakhtysh I site area, ? = 56°48′ N, λ = 40°33′ E) during the time interval of 5–3 ka BC. The geomagnetic field intensity varied mainly within the range of 30–60 μT. In the first half of the 5th millennium BC, the mean level of geomagnetic field intensity was about 35 μT. In the second half of the 5th–early 4th millennium BC, it rose to about 50 μT and then decreased again to reach a mean value of about 40 μT in the period of 4–3 ka BC. Comparison of the geomagnetic field intensity variation based on the obtained data and the data on the Caucasus region for the same time interval demonstrates a certain similarity.     

Archaeomagnetic studies of materials from the Gorelyi Les and Ust-Khaita monuments (Eastern Siberia)

Archaeomagnetic studies of materials from archaeological monuments of the Irkutsk and Baikal regions provided new constraints on the geomagnetic intensity variation in Eastern Siberia for the interval from the 5th millennium BC through the 1st millennium AD. Material from the Gorelyi Les and Ust-Khaita multilayer archaeological monuments of the Irkutsk region is dated according to layer depths of deposits. Data on the geomagnetic intensity obtained from archaeomagnetic studies corroborate the validity of this method of dating. It is established that the average level of the geomagnetic intensity smoothly rose in the interval from the 5th millennium BC through the 1st millennium AD, with faster variations being superimposed on this trend. The pattern of the geomagnetic intensity variation is similar to those in other Eurasian regions.     

The geomagnetic field in the 20th century

The continuous spatial-temporal model of variations in the main geomagnetic field in the 20th century has been elaborated. All available data—from the navigation to the satellite surveys at the beginning and end of the century, respectively—have been used to construct the model. Since the accuracy of measurements was different during the century and the data are nonuniformly distributed over the Earth’s surface, the methods for regulating solutions based on global parameters of the magnetic field and its secular variation, invariant on the simulation interval, have been used to correct the model. The secular variation model has been represented as the sum of the models obtained by means of expansion in terms of natural orthogonal components. The conclusions that the character of field variations is complex have been made and the spatial and temporal characteristics of the secular variations of different origin have been estimated based on the simulation results.     

An estimate of late Pleistocene geomagnetic intensity variation from Sulu Sea sediments

Sediments from Site 769 of the Ocean Drilling Program's Leg 124 provide a record of geomagnetic intensity variation over the past 110 ky. Using continous shipboard measurements exclusively, I estimate the variation in the geomagnetic field strength by employing low-field magnetic susceptibility as a normalization parameter for the measured remanence intensity. By calibrating the resultant relative paleointensity record against previously available Holocene age estimates of absolute paleointensity, I derive an estimate of virtual dipole moment since 110 ka. The record obtained from these Sulu Sea sediments is strikingly like that previously obtained from sediments of a similar age in the Mediterranean Basin with distinct intervals of low intensity near 15, 20, 40 and 65–70 ka. The Sulu sediments also indicate a low-intensity feature near 108 ka. Important differences in paleointensity estimates obtained from these different regions for the interval between 30 and 20 ka suggest that a relatively large non-dipolar component of the geomagnetic field might have been present at that time.     

Archaeomagnetic determination of the ancient intensity of the geomagnetic field in Tamilnadu,India

A detailed study of the ancient intensity of the Earth's magnetic field in Tamilnadu, India is presented using pottery, bricks, tiles etc., obtained from the excavations that have been carried out at some of the important places of historical and archaeological interest. An attempt is made to reconstruct the secular variation of the geomagnetic field intensity. The results reported here reveal considerable changes in the Earth's magnetic field in this region during the past 2400 y. It is observed that the intensity of the geomagnetic field has been previously 57% greater than at present.     

苏、 鲁、 豫、 皖交界及南黄海地区地磁监测与分析

通过在苏、 鲁、 豫、 皖交界及南黄海地区开展地磁基本场矢量测量、 数据处理和分析, 计算了该区域地磁基本场和地磁异常场总强度和水平强度的曲面样条模型, 并绘制相应的地磁图和地磁异常图, 探索研究局部地磁基本场的变化特征。 分析结果表明, 通过区域地磁基本场矢量测量, 能相对精细地反应区域地磁基本场空间分布, 分辨存在的地磁基本场异常, 为地震中长期预报提供科学数据和相关地球物理场变化背景。     

二维电离层发电机理论模式及其初步应用

在地理坐标系下推导出二维电离层发电机理论方程,采用逐线迭代法求解得到全球二维电离层发电机电流函数,进而得到电离层发电机电流和电场.模式中使用的电导率是根据外部经验模式给出的背景大气和电离层参数,采用理论公式计算得出;输入的中性风场和磁场分别由HWM93和IGRF2000模型给出,该电离层发电机理论模式很好地给出了全球Sq电流形态及电离层E层发电机电场的基本特征.利用该模式研究了外部模式风场以及地磁场随高度的变化对模拟结果的影响,发现在90~180 km高度上,风场随高度变化对电流影响较大,而地磁场影响较小;重点模拟研究了地磁平静时期,Sq电流涡旋中心位置和总电流强度的变化规律,初步研究发现,电流中心位置在地理纬度±30°附近,不同的地方时电流随地磁纬度线平行移动,且南北半球两个电流涡中心电流强度之和变化不大.分析发现这种规律与发电机高度上的磁场总强度及地磁倾角的全球分布有很好的相关性.     

A Regional Archaeomagnetic Model for the Palaeointensity in Europe for the last 2000 Years and its Implications for Climatic Change

The SCHA.DI.00 directional model for the geomagnetic field in Europe for the last 2000 years (Pavón–Carrasco et al., 2008) has been updated by modelling the palaeointensity. This model, SCHA.DI.00, was developed from available Bayesian European Palaeosecular Variation Curves using the regional Spherical Cap Harmonic Analysis technique. The comparison of the palaeosecular variation curves, given by the regional model, with available archaeomagnetic data not used in its development showed an improvement with respect to the fit obtained by global archaeomagnetic models. In this paper advantage is taken of recently published palaeointensity databases to develop a complete (direction and intensity) regional archaeomagnetic model for the last 2000 years valid for the European region: the SCHA.DI.00–F model. Not only does this complete model provide an improvement for example for archaeomagnetic data studies, but it is also shown that this new regional model can be used to study the recently proposed link between the centennial secular variation of the geomagnetic field and climate change. The pattern of the archaeosecular variation of the field intensity obtained by SCHA.DI.00–F seems to verify the hypothesis presented by Gallet et al. (2005) about a possible (causal) connection between changes in the geomagnetic field intensity and in climate parameters, opening the door for more discussions on this challenging subject.     

Geomagnetic Field Variations as Determined from Bulgarian Archaeomagnetic Data. Part II: The Last 8000 Years

The knowledge about past secular variations of the geomagnetic field is achieved on the basis of archaeomagnetic researches of which the Bulgarian studies form an extended data set. In Part I (Kovacheva and Toshkov, 1994), the methodology used in the Sofia palaeomagnetic laboratory was described and the secular variation curves for the last 2000 years were shown. In Part II (this paper), the basic characteristics of the prehistoric materials used in the archaeomagnetic studies are emphasised, particularly in the context of the rock magnetic studies used in connection with palaeointensity determinations. The results of magnetic anisotropy studies of the prehistoric ovens and other fired structures are summarised, including the anisotropy correction of the palaeointensity results for prehistoric materials, different from bricks and pottery. Curves of the direction and intensity of the geomagnetic field during the last 8000 years in Bulgaria are given. The available directional and intensity values have been used to calculate the variation curve of the virtual dipole moment (VDM) for the last 8000 years based on different time interval averages. The path of virtual geomagnetic pole (VGP) positions is discussed.     

Archeomagnetic studies of ceramics from the archeological monument in Ubeda,Spain

The archaeomagnetic study of the ceramics from the multilayered archeological monument Ubeda in Spain provided the data on the geomagnetic field strength in the period of accumulation of cultural deposits. According to the results obtained for the Ubeda monument of the Bronze Age and the La Motilla Del Azuer multilayer archaeological monument dated to the second millennium BC, the time interval of accumulation of the Ubeda cultural deposits likely spans from the last quarter of the 19th to 18th centuries BC. The sharp decrease in the geomagnetic field strength in the 19th century BC. established against the obtained data is consistent with the archaeomagnetic results for other Eurasian regions and can be used for correlating the ages of various archeological monuments and stages of culture.     

Direction and relative paleointensity of the geomagnetic field in the middle and later pleistocene from paleomagnetic data of the Roxolany section (Ukraine)

The lower part of the Roxolany section (Ukraine) is studied, and paleomagnetic and petromagnetic characteristics of rock samples are obtained for the time interval 300-75 ka. Detailed curves of variations in angular parameters of the geomagnetic field are constructed in the entire time interval, and curves of variations in the relative paleointensity are obtained for the interval 300-180 ka. Using the values of the angular parameters and the deviations of the virtual geomagnetic pole from the position of the stationary field, anomalous directions compatible with the Jamaica excursion are identified in the intervals 250-249 and 221-220 ka. The geomagnetic field evolution is studied by methods of wavelet analysis, and the field generation process is shown to vary in the interval 300-180 ka.     

Variations of angular elements of the geomagnetic field in Europe during the last 24 centuries

The analysis of variations in angular elements of the geomagnetic field during the period since 350 B.C. to the present day according to the findings from the study of thermal magnetization of baked archaeological samples from England, France, and East Europe showed that the key feature in the behavior of the geomagnetic inclination in all three regions is a millennial variation. The trend in the behavior of the inclination of the geomagnetic field can be regarded as a manifestation of a variation with a characteristic time scale of several thousand years. Despite the general likeness of variations in inclination and declination of the ancient geomagnetic field, they also exhibit a noticeable dissimilarity. The paths of the virtual geomagnetic pole reconstructed from the variations of angular elements of the geomagnetic field in East Europe indicate that the geomagnetic polar motion is quasi-cyclic. The duration of the first cycle was about 1000 years, while the second cycle has not been completed due to the change of the motion to the opposite direction in the middle of the XVII century.     

IGRF-11描述的2005-2010年中国地区地磁长期变化及其误差分析

第11代国际地磁参考场(IGRF-11)是国际地磁学与高空物理学联合会(IAGA)于2009年12月提出的最新与比较准确的IGRF.根据IGRF-11模型,计算了2005-2010年中国地区地磁长期变化(SVC).IGRF-11所描述的2005-2010年中国地区地磁长期变化与实际观测的地磁长期变化(SVO)是基本一致的,但亦有明显差异.分析比较了在中国地区34个台站上的SVO与SVC之间的差异,并得到了它们之间的差值及其均方误差σ,对于地磁偏角和倾角,σ分别为0.35′/a与0.53′/a;对于地磁总强度、水平分量、北向分量、东向分量与垂直分量,σ分别为5.12nT/a,8.91nT/a,8.89nT/a,3.27nT/a与3.59nT/a.引起IGRF-11所描述的2005-2010年中国地区地磁长期变化的误差原因是:中国地区的区域性与局部性的磁异常、IGRF忽略了外源场与IGRF模型的截断阶数、全球台站与测点的分布不均匀、地磁观测误差等因素.由于中国地磁模型(CGM)优于IGRF模型,并能比较准确地描述中国地区地磁场及其长期变化,故在实际应用中应选用CGM.     

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。