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921.
922.
923.
Lunar daily geomagnetic variations in New Zealand 总被引:1,自引:0,他引:1
J. D. McKnight 《Geophysical Journal International》1995,122(3):889-898
924.
SUMMARY
This work quantifies the extent to which disturbance phenomena contribute to the observed geomagnetic field on the time-scale of months to years. A deterministic approach was adopted in which geomagnetic monthly means were analysed in the time domain. By presupposing the time dependence of the external and induced field variations, which we assume to vary as the aa geomagnetic index, we arrived at an estimate of the relative amplitude of the disturbance to each component of the field at a number of observatories. In all some 58 000 geomagnetic monthly means from 59 observatories operating this century were analysed. Special attention was paid to the selection and validation of the data as otherwise the numerical computations would have been unduly compromised.
The results consist of 177 estimates of the relative amplitude of disturbance, one for each of three orthogonal components north ( X ), east ( Y ) and vertically down ( Z ) at each observatory. The disturbance to the X component was found to be consistently negative over the whole of the Earth's surface with an intensification in auroral regions. The disturbances to the Z component were found to be smaller than that for X except in high latitudes. Mean disturbances to the Y component were smaller still. Results were in general consistent with the dipole field of the magnetospheric ring current, aligned with, though of opposite polarity to, the Earth's main field. Typical amplitudes of the mean disturbance field from month to month were of the order 10 nT.
The results can be used to estimate the variation of the disturbance field. Subtracting this from both monthly and annual means yields an improved estimate of the field originating in the core and its secular variation. Some examples are presented. 相似文献
This work quantifies the extent to which disturbance phenomena contribute to the observed geomagnetic field on the time-scale of months to years. A deterministic approach was adopted in which geomagnetic monthly means were analysed in the time domain. By presupposing the time dependence of the external and induced field variations, which we assume to vary as the aa geomagnetic index, we arrived at an estimate of the relative amplitude of the disturbance to each component of the field at a number of observatories. In all some 58 000 geomagnetic monthly means from 59 observatories operating this century were analysed. Special attention was paid to the selection and validation of the data as otherwise the numerical computations would have been unduly compromised.
The results consist of 177 estimates of the relative amplitude of disturbance, one for each of three orthogonal components north ( X ), east ( Y ) and vertically down ( Z ) at each observatory. The disturbance to the X component was found to be consistently negative over the whole of the Earth's surface with an intensification in auroral regions. The disturbances to the Z component were found to be smaller than that for X except in high latitudes. Mean disturbances to the Y component were smaller still. Results were in general consistent with the dipole field of the magnetospheric ring current, aligned with, though of opposite polarity to, the Earth's main field. Typical amplitudes of the mean disturbance field from month to month were of the order 10 nT.
The results can be used to estimate the variation of the disturbance field. Subtracting this from both monthly and annual means yields an improved estimate of the field originating in the core and its secular variation. Some examples are presented. 相似文献
925.
926.
927.
Time changes in transfer functions of short period geomagnetic variations in 28 years from 1960 through 1987 are studied,
systemically and in detail in this paper. The results indicate that: (1) It is evident that seasonal and secular changes in
the transfer functionsA at exist the Guangzhou Geomagnetic observatory. The characteristics for seasonal changes are large in summer and smaller
in winter with main cycles of 12 and 6 months. The characteristic for secular change is a descend with a rate of 0.0025 per
year. The seasonal and secular changes in transfer functionsB are not evident. (2) The direction of Parkinson vector at Guangzhou geomagnetic observatory is clearly affected by the ocean,
and is associated with coastal effect. (3) The values of the transfer function A and B are related to geomagnetic activity
ata=0.05. Secular change is not related to geomagnetic activity, maybe it is affected in a great measure by earth conductivity
change.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica sinica,13, 480–488, 1991.
This study is part supported by Chinese Joint Seismological Science Fundation. 相似文献
928.
Crossing Honghe fracture in Yunnan Province two measuring profiles were set up, each measuring profile consisted of 8 observing
sites. Three component geomagnetic variation observations were carried out continuously and simultaneously along each profile.
Induction arrows were calculated for the periods from 8 min to 60 min. There exists a reversal axis of induction arrow between
Eryuan, Xiaguan, Weishan, Mejiang and Yongping, Yunxian, Lincang, Simao. The real arrows reverse from one side of the axis
to another side and the magnitude of the real induction arrows attenuates with increase in distance from the axis, the attenuation
in northeast side of the axis is slightly less than that in southwest side. The real induction arrows of shorter periods are
greater than those of longer periods at most of the observing sites. According to the features of the real induction arrows
and by use of numerical calculation we tried to look for the restriction which was to be attached to the possible high conductivity
zone in the area under investigation. It shows that there is a high conductivity belt west of Honghe fracture which tilts
northeastward and there is a high conductor cover over the high conductivity belt beneath most of the observing sites
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 201–210, 1992. 相似文献
929.
In this paper, the two metnods, rectangular spectrum (RS) and maximum entropy power spectrum (MES), have been used in calculating
the geomagnetic structures of the crust in Haicheng and its adjacent areas and carrying out the geomagnetic stratification
of the crust. The result of the research indicates that the crust can be devided into such three layers as nonmagnetic layer,
magnetic layer and regressive magnetic layer from the top to the bottom. It is also found the distribution of the geomagnetic
bottom interface (Curie surface) is consistent with the lower interface of the upper crust and the top interface of the middle
crust of the velocity structure of the crust. It is very interesting that the Haicheng earthquake of Feb. 4, 1975,M 7.3 occurred at the depth gradient belt of the Curie isotherm surface. So, to research on the geomagnetic layers and the
distribution characteristics of the Curie isotherm surface is meaningful in judging potential seismic foci.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 448–454, 1993.
The data of velocity and electricity materials used in this paper are as reference from the related materials of the maps
and directions etc. of Donggou-Haicheng-Dong Ujimqin Qi Geoscience Transect by Prof. Zao-Xun LU, Huai-Kuan XIA and others. 相似文献
930.
根据全国地磁台站资料质量评审中提供的信息,对全国台站1990-1991年地磁场三分量的年均值进行了分析,给出了年变率分布特征及相应的等值线图。 相似文献