Journal of geomagnetism and geoelectricity最新文献_第10页

Mesospheric Ozone Density Profiles in the Polar Region 极地地区的中间层臭氧密度分布

Journal of geomagnetism and geoelectricity Pub Date : 1997-05-20 DOI: 10.5636/JGG.49.675

Hiromasa Yamamoto, Ken-ichi Yajima, H. Sekiguchi, T. Makino

引用次数: 1

Identification of the current system associated with a partially reversed equatorial electrojet 与部分逆转的赤道电喷流有关的电流系统的鉴定

Journal of geomagnetism and geoelectricity Pub Date : 1997-05-20 DOI: 10.5636/JGG.49.633

M. James, R. G. Rastogi, D. Rao

引用次数: 3

Magnetic Anomaly Fields Determined from Gradient Measurements at Stratospheric Altitudes and from Magsat Satellite Data 由平流层高度梯度测量和Magsat卫星数据确定的磁异常场

Journal of geomagnetism and geoelectricity Pub Date : 1997-05-20 DOI: 10.5636/JGG.49.689

Y. Tsvetkov, N. Rotanova, V. Oraevsky, S. Odintsov

引用次数: 1

Speleothem Palaeosecular Variation Records from China: Their Contribution to the Coverage of Holocene Palaeosecular Variation Data in East Asia 中国洞穴古世变化记录对东亚全新世古世变化数据覆盖的贡献

Journal of geomagnetism and geoelectricity Pub Date : 1997-04-20 DOI: 10.5636/JGG.49.485

S. Openshaw, A. Latham, J. Shaw

{"title":"Speleothem Palaeosecular Variation Records from China: Their Contribution to the Coverage of Holocene Palaeosecular Variation Data in East Asia","authors":"S. Openshaw, A. Latham, J. Shaw","doi":"10.5636/JGG.49.485","DOIUrl":"https://doi.org/10.5636/JGG.49.485","url":null,"abstract":"Five stalagmitic speleothems from two caves in Sichuan province China, have yielded data on the palaeosecular variation (PSV) of the past 8.9 ka. The uranium-thorium disequilibrium method has been utilised in order to estimate the age of each record. Due to the high detrital load contributing some allogenic thorium, age corrections had to be applied to most sub-samples. The directional agreement between coeval central and lateral sub-samples where growth layers are horizontal and steeply dipping respectively suggests that inclination errors are absent in these speleothems. Correlation between features of declination and inclination in the individual records, even after time-averaging, are reasonable indicating a local consistency in recorded PSV and adding to the reliability of the palaeomagnetic and age data. Comparisons between our speleothem directions and the directions of the modern field drifted westward past our site at 0.13° yr -1 suggests westward drifting of non-dipole sources during the past 2.8 ka. Using directional data from two speleothems with the longest growth periods a composite curve covering the past 8.9 ka has been constructed. The resulting VGP path again indicates predominantly westward drift. The declination and inclination features of these speleothems also compare reasonably with features of PSV in contemporaneous records from China and Japan.","PeriodicalId":156587,"journal":{"name":"Journal of geomagnetism and geoelectricity","volume":"49 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129222283","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 17

Comparison of Directional Secular Variation of the Geomagnetic Field between Britain and S. E. Europe 英国与欧洲东南部地磁场方向长期变化的比较

Journal of geomagnetism and geoelectricity Pub Date : 1997-04-20 DOI: 10.5636/JGG.49.507

D. Tarling, M. Kovacheva

{"title":"Comparison of Directional Secular Variation of the Geomagnetic Field between Britain and S. E. Europe","authors":"D. Tarling, M. Kovacheva","doi":"10.5636/JGG.49.507","DOIUrl":"https://doi.org/10.5636/JGG.49.507","url":null,"abstract":"Archaeomagnetic data from “Britain” (46°N-58°N, 12°W-8°E) and S. E. Europe (37°N-49°N, 15°1-25°E) for the last 2, 300 years are selected on the basis of the reported reliability of their archaeological age as well as the precision in the determination of their mean site values. When grouped into mean values for each decade, clear trends are visible for both areas, although individual sites show somewhat anomalous values that are largely attributed to in situ site disturbances. The trend lines, when smoothed by a two-point running mean, appear to give a good representation of the geomagnetic secular variation in these two areas. Comparison between the areas, that are 9° in latitude and 26° longitude apart, suggests that an axial geocentric dipole could largely account for the average difference in inclination. The quasi-sinusoidal patterns are more complex in declination than inclination, as previously proposed on less reliable data. There are visual indications of periodicities of some 300 years in inclination and some 400 years in declination but periodicities longer than the time range represented by the data are present. The time of occurrence of maxima and minima for both declination and inclinations suggests that both westward and eastward drift of the geomagnetic field patterns have occurred.","PeriodicalId":156587,"journal":{"name":"Journal of geomagnetism and geoelectricity","volume":"159 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121312247","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 4

Variation of Rock Magnetic Parameters and Paleointensities over a Single Holocene Lava Flow 单次全新世熔岩流岩石磁性参数和古强度的变化

Journal of geomagnetism and geoelectricity Pub Date : 1997-04-20 DOI: 10.5636/JGG.49.523

H. Böhnel, J. Morales, C. Caballero, L. Alva, G. McIntosh, S. González, G. Sherwood

{"title":"Variation of Rock Magnetic Parameters and Paleointensities over a Single Holocene Lava Flow","authors":"H. Böhnel, J. Morales, C. Caballero, L. Alva, G. McIntosh, S. González, G. Sherwood","doi":"10.5636/JGG.49.523","DOIUrl":"https://doi.org/10.5636/JGG.49.523","url":null,"abstract":"A recent (2000 BP) lava flow from central Mexico has been sampled along a vertical profile with 55 cores covering a total flow thickness of 6.6 m. A wide range of physical and magnetic parameters have been studied to characterise the samples: Curie temperature and saturation magnetisation as intrinsic properties; density, magnetic susceptibility and remanence intensity as bulk properties; Konigsberger Q-factor and hysteresis parameters as coercivity parameters. All parameters vary smoothly over the profile, most probably due to grain size variation of the magnetic minerals present in the samples. Optical observations indicate that the main opaque minerals are deuterically oxidised titanomagnetites (C3-C5) and ilmenites (R2-R3), which increase in size away from the edges of the flow. Paleointensity (PI) was determined using the double heating Thellier-Thellier method with pTRM checks. According to reliability parameters (f-, g-, and q-factor) the obtained PIs are of reasonable to good quality. PI shows marked variation with vertical position in the flow, across a range of about 25 to 125 μT, with most samples having a PI between 50 and 100 μT. The flow-mean PI of 72 μT is higher than the present day field, consistent with global data for this time-period. No obvious correlation could be found between PI and any other measured parameter. The variation of PI with vertical position in the flow may show some systematic behaviour. It is important, therefore, to sample a flow both horizontally and vertically in order to obtain a reliable paleointensity.","PeriodicalId":156587,"journal":{"name":"Journal of geomagnetism and geoelectricity","volume":"186 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123552737","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 47

Paleosecular Variation in Field Directions Due to Randomly Varying Gauss Coefficients. 高斯系数随机变化引起的古长期场方向变化。

Journal of geomagnetism and geoelectricity Pub Date : 1997-04-20 DOI: 10.5636/JGG.49.615

M. Kono

{"title":"Paleosecular Variation in Field Directions Due to Randomly Varying Gauss Coefficients.","authors":"M. Kono","doi":"10.5636/JGG.49.615","DOIUrl":"https://doi.org/10.5636/JGG.49.615","url":null,"abstract":"Expressions are derived for the magnetic field directions produced by randomly varying Gauss coefficients. This approach was pioneered by Constable and Parker (1988), and followed by Kono and Tanaka (1995) and Kono and Hiroi (1996). The present treatment is a sequel to the latter two. The basic assumption is that the magnitude of the axial dipole component is much larger than all the other terms: equatorial dipoles or nondipole components. It is also assumed that, in a sufficiently long time interval, Gauss coefficients, g l m and h l m , behave as independent random variables that have the first and second moments defined. General expressions are obtained for the field directions (inclination I and declination D). Paleosecular variation (PSV) of field directions is formulated as latitude dependences of statistical parameters (the means and variances) of inclination and declination. It is possible to derive a family of PSV models by specifying the statistical nature of individual Gauss coefficients, i.e., assigning means and variances to them. In this paper, we describe a homogeneous background model (HBM), which consists of a large axial dipole component (g 1 0 ) and other harmonics that have zero mean and variances decreasing exponentially with the degree of the harmonic. This model is too homogeneous to reproduce observed latitudinal variation of secular variation, but is quite useful to identify the harmonics that have effect that is larger than produced by the HBM. Comparison with paleomagnetic data obtained from volcanic rocks of 0-5 Ma ages (Quidelleur et al., 1994) shows that it is necessary that the mean of g 2 0 must be about 5% of the mean of g 1 0 , and that g 2 1 (or h 2 1 ) should have about three to four times as large an effect as suggested by the HBM. The former conclusion is consistent with the result of Constable and Parker (1988), while the latter conclusion substantiates the similar conclusion obtained by Kono and Tanaka (1995) by the analysis of the scatter of the virtual geomagnetic poles (VGPs).","PeriodicalId":156587,"journal":{"name":"Journal of geomagnetism and geoelectricity","volume":"44 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128354309","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 11

Mineral magnetic studies of archaeological samples : Implications for sample selection for paleointensity determinations 考古样品的矿物磁性研究:古强度测定样品选择的意义

Journal of geomagnetism and geoelectricity Pub Date : 1997-04-20 DOI: 10.5636/JGG.49.567

Yulong Cui, K. Verosub, A. Roberts, M. Kovacheva

引用次数: 19

A North American Archaeomagnetic Database. 北美考古磁数据库。

Journal of geomagnetism and geoelectricity Pub Date : 1997-04-20 DOI: 10.5636/JGG.49.519

R. Sternberg, William L. Deaver, Elizabeth A. Kuter, Adrienne L. Kiley

引用次数: 5

Paleointensity of the Earth's Magnetic Field for the Past 400 Ma : Evidence for a Dipole Structure during the Mesozoic Low 过去400 Ma地球磁场的古强度:中生代低潮期间偶极子结构的证据

Journal of geomagnetism and geoelectricity Pub Date : 1997-04-20 DOI: 10.5636/JGG.49.601

M. Perrin, V. Shcherbakov

{"title":"Paleointensity of the Earth's Magnetic Field for the Past 400 Ma : Evidence for a Dipole Structure during the Mesozoic Low","authors":"M. Perrin, V. Shcherbakov","doi":"10.5636/JGG.49.601","DOIUrl":"https://doi.org/10.5636/JGG.49.601","url":null,"abstract":"Despite the limited number of paleointensity data available for the last 400 Ma, some general features of the magnetic field in the past can be drawn from their analysis. A mild selection applied to the set drastically reduced the number of determinations, underscoring the unequal quality of the paleointensity estimates at hand and the clear need for many more new reliable studies. However, with or without selection, the record is characterized by a succession of periods with alternatively low and high fields, but data available are yet insufficient to propose any model of transition between both regimes. For the last 400 Ma, the dipole nature of the main field is preserved. This is also true when only data from the Mesozoic Dipole Low (120-260 Ma) are considered. Moreover it is shown that the Mesozoic data are very unlikely to represent an insufficient sampling of a Neogene-type field. These last observations strengthen the reality of this long period where the intensity of the main field was roughly only one third of the present-day value. A possible relation between field strength and secular variation (approximated by standard deviation) appears to exist, although this remark is compromised by the existence of a similar relation between standard deviation and number of determinations. The distribution of all Virtual Dipole Moments is log-normal, as shown before, but when only the selected data set is considered the distribution is clearly bi-modal. An oscillatory or bimodal paleointensity behaviour rather than a monotone variation is not at all unexpected given the highly non-linear geodynamo equations.","PeriodicalId":156587,"journal":{"name":"Journal of geomagnetism and geoelectricity","volume":"18 6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134327765","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 116