Journal of geomagnetism and geoelectricity最新文献_第7页

On a Realistic Geodynamo Model. 关于一个现实的地球发电机模型。

Journal of geomagnetism and geoelectricity Pub Date : 1997-08-20 DOI: 10.5636/JGG.49.1035

Stanislav I. Bragivsky

引用次数: 3

Occurrence Characteristics of the Preliminary Impulse of Geomagnetic Sudden Commencement Detected at Middle and Low Latitudes. 中低纬度探测到的地磁突然启动初脉冲的发生特征。

Journal of geomagnetism and geoelectricity Pub Date : 1997-08-20 DOI: 10.5636/JGG.49.1001

Yuji Yamada, M. Takeda, T. Araki

{"title":"Occurrence Characteristics of the Preliminary Impulse of Geomagnetic Sudden Commencement Detected at Middle and Low Latitudes.","authors":"Yuji Yamada, M. Takeda, T. Araki","doi":"10.5636/JGG.49.1001","DOIUrl":"https://doi.org/10.5636/JGG.49.1001","url":null,"abstract":"The occurrence frequency of preliminary impulse (PI) of geomagnetic sudden commencements was statistically studied using the geomagnetic records of H-component at Fredericksburg (FRD; 49.0° geomagnetic latitude) and San Juan (SJG; 29.2°). In the daytime, positive PI predominantly occurs before noon and negative PI in the afternoon. These features, which are the same as those of high-latitude PI, indicate that high-latitude ionospheric currents responsible for PI extends toward middle and low latitudes. Almost all PIs detected in the nighttime are negative at FRD though the occurrence rate is much smaller than in the daytime. The diurnal variation of the occurrence rates of PI shows a drastic seasonal change at SIG, which is probably caused by a seasonal variation of the ionosphere. No correlation between the occurrence rates and the solar activity was found at either observatories. Ionospheric currents which are driven by a pair of field-aligned currents were numerically calculated on the assumption of the stationary state, and the geomagnetic field variation caused by the three-dimensional currents is simulated. Although the symmetric distribution of the field-aligned currents with respect to the noon-midnight meridian has been assumed, the calculated diurnal variation of magnetic field exhibits a severe deflection from the symmetry in middle and low latitudes.","PeriodicalId":156587,"journal":{"name":"Journal of geomagnetism and geoelectricity","volume":"95 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132996431","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

An Audiomagnetotelluric View of the Atera Fault. 阿特拉断层的音频大地电磁观测。

Journal of geomagnetism and geoelectricity Pub Date : 1997-08-20 DOI: 10.5636/JGG.49.1065

Y. Ogawa, Y. Honkura

引用次数: 7

Preliminary Magnetotelluric Modeling in the Nikko Volcanic Area -Potential Break of Fluid Trap by Volcanic Intrusion 日光火山区大地电磁初步模拟——火山侵入流体圈闭的潜在断裂

Journal of geomagnetism and geoelectricity Pub Date : 1997-08-20 DOI: 10.5636/JGG.49.1073

Y. Ogawa, Y. Honkura, F. Ohtani, H. Kuroki, Y. Mitsuhata

引用次数: 3

Middle and High Latitude Whistlers Observed Simultaneously in a Low Latitude Station at Agra 阿格拉低纬度站同时观测到的中高纬度哨声

Journal of geomagnetism and geoelectricity Pub Date : 1997-08-20 DOI: 10.5636/JGG.49.995

Birbal Singh

引用次数: 4

Spherical Harmonic Analysis in Terms of Unevenly Distributed Observation Points and Its Applications to Geomagnetic Data 非均匀分布观测点的球谐分析及其在地磁资料中的应用

Journal of geomagnetism and geoelectricity Pub Date : 1997-08-20 DOI: 10.5636/JGG.49.1013

E. Mochizuki, Y. Yokoyama, Itsujiro Shimizu, Y. Hamano

引用次数: 4

The Interpretation of Geomagnetic Field Reversal on the Basis of Fluctuation Growth by Using Disk Dynamo Model. 基于波动增长的磁碟发电机模型解释地磁场反转。

Journal of geomagnetism and geoelectricity Pub Date : 1997-08-20 DOI: 10.5636/JGG.49.1049

S. Kondo

{"title":"The Interpretation of Geomagnetic Field Reversal on the Basis of Fluctuation Growth by Using Disk Dynamo Model.","authors":"S. Kondo","doi":"10.5636/JGG.49.1049","DOIUrl":"https://doi.org/10.5636/JGG.49.1049","url":null,"abstract":"Based on the viewpoint of fluctuation growth, we analyze and discuss the geomagnetic field reversal, focusing on a three-disk dynamo model, mainly on the effect of mutual inductance on dynamic behaviors. If mutual inductance is large, which means strong interaction between neighboring disks and their associated circuits, then a very slight fluctuation of electric current is found to be greatly enhanced after a short incubation time. On the contrary, after a long incubation time, fluctuation growth is very slow when mutual inductance is small. Therefore the degree of interaction is related to the length of incubation time: the stronger the interaction, the shorter incubation time. The analogy between the disk dynamos and the geomagnetic field reversal patterns implies slight fluctuations are greatly enhanced during the period for the past 25 Ma, whereas fluctuation growth is very slow during the period of the Cretaceous Superchron, implying that mutual inductance is dependent on time. Hence, disk dynamo calculations including time dependence of mutual inductance are found to explain geomagnetic field reversal pattern qualitatively. From the mathematical viewpoint, numerical solutions for time dependent mutual inductance is found to be obtained by frequency modulation (FM) over those for time independent mutual inductance.","PeriodicalId":156587,"journal":{"name":"Journal of geomagnetism and geoelectricity","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125031401","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: 1

The Impact of Solar Irradiance on the Maunder Minimum Climate 太阳辐照度对蒙德极小期气候的影响

Journal of geomagnetism and geoelectricity Pub Date : 1997-07-20 DOI: 10.5636/JGG.49.957

B. Mendoza, R. Garduño, J. Adem

引用次数: 1

Effect of Anomalous Cross-Field Diffusion on the Field-Aligned Current Generation 反常跨场扩散对场向电流产生的影响

Journal of geomagnetism and geoelectricity Pub Date : 1997-07-20 DOI: 10.5636/JGG.49.923

Takashi Yamamoto, S. Inoue, C. Meng

{"title":"Effect of Anomalous Cross-Field Diffusion on the Field-Aligned Current Generation","authors":"Takashi Yamamoto, S. Inoue, C. Meng","doi":"10.5636/JGG.49.923","DOIUrl":"https://doi.org/10.5636/JGG.49.923","url":null,"abstract":"First, on the basis of the satellite observations of the broadband electrostatic noise and the Alfven wave noise in the auroral magnetosphere, within a frame of the quasi-linear theory we show that the proton (anomalous cross-field) diffusion coefficient averaged over the flux tube is likely to reach a significant fraction of the Bohm rate at least in the disturbed periods. Second, as an extension of recently proposed model that a pair of the region 1 and region 2 field-aligned currents (FACs) can be generated as a result of \"natural distortion\" of the hot plasma torus (HPT) in the magnetosphere under the influence of the usually prevailing convection with twin vortex cells (when the interplanetary magnetic field (IMF) is southward), we study the possible effect of the anomalous cross-field diffusion on the large-scale FACs resulting from the HPT polarization. In the magnetosphere, the hot (≥ 1 keV) plasma particles are primarily distributed in a magnetic shell which is connected to two ovals of diffuse auroras on the northern and southern polar ionospheres. Such hot plasma population is called the hot plasma torus (HPT). The numerical calculations specifically show that primary modification of the FAC pattern by this effect is the appearance of the triple FAC structure (i.e., upward FAC zone sandwiched between two downward FAC zones) in the midnight sector, which can be identified from the satellite observations at least during substorm periods. As a direct consequence of formation of such a triple FAC structure, the Harang discontinuity appears in the electric potential pattern. Thus the formation of the Harang discontinuity can be understood as a result of the HPT polarization by both effects of magnetic drift and anomalous cross-field diffusion.","PeriodicalId":156587,"journal":{"name":"Journal of geomagnetism and geoelectricity","volume":"144 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125645359","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: 6

Self-Potential Changes and Subsurface Hydrothermal Activity Accompanying the 1990-1995 Eruption of Unzen Volcano 1990-1995年云仙火山喷发伴随的自电位变化和地下热液活动

Journal of geomagnetism and geoelectricity Pub Date : 1997-07-20 DOI: 10.5636/JGG.49.977

T. Hashimoto

{"title":"Self-Potential Changes and Subsurface Hydrothermal Activity Accompanying the 1990-1995 Eruption of Unzen Volcano","authors":"T. Hashimoto","doi":"10.5636/JGG.49.977","DOIUrl":"https://doi.org/10.5636/JGG.49.977","url":null,"abstract":"The evolution of a hydrothermal system beneath the Unzen Volcano, one of the dacitic volcanoes in Shimabara peninsula, southwest Japan, was investigated by self-potential (SP) observations during the 1990-1995 eruption events. SP changes accompanying the eruption can be divided into three stages. In the first stage, March through June of 1991, the rapid growth of a distinct positive SP anomaly was detected by continuous observation in the vicinity of a lava dome which began extrusion in May 1991. The positive anomaly is thought to be caused by hydrothermal upflows induced around the intruded magma through electrokinetic coupling. In the second stage, July 1991 through December 1993, the lava dome erupted in an exogenous manner. The growth of a dipolar SP anomaly was detected by repeated surveys during this stage. The cause of this SP change is thought to be electrokinetic potentials associated with shallow hydrothermal circulation which grew at the west of the lava dome for over two years. In the third stage, from the beginning of 1994, the dome growth became endogenous. SP showed concentric increase around the dome. This SP change probably suggests the expansion of upflow zone at high temperature in shallow levels.","PeriodicalId":156587,"journal":{"name":"Journal of geomagnetism and geoelectricity","volume":"87 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124140145","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: 5