巻号一覧
36 巻, 3 号
選択された号の論文の3件中1～3を表示しています
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M. J. S. JOHNSTON, R. J. MUELLER, R. H. WARE, P. M. DAVIS1984 年 36 巻 3 号 p. 83-95
発行日: 1984年
公開日: 2010/09/14
ジャーナル フリーA linear regression on standard deviations of differential proton magnetometer measurements at distances from a few meters to 50 kilometers indicates a standard deviation of hourly means that varies with site separation as σ=a+bd where a=0.07±0.08nT, b=0.01±0.003nT/km and d is the site separation in kilometers. At a few meters separation, for sites with low cultural noise in both seismically inactive and active regions, the standard deviation of hourly mean data has a mean of 0.12±0.03nT for instruments with 0.25nT sensitivity and 0.07±0.01nT for instruments with 0.125nT sensitivity. The least-count noise contributions are expected to be less than 0.06nT and 0.03nT, while undetermined instrument noise appears to contribute 0.10 and 0.06nT respectively. Instrument temperature sensitivity does not exceed 0.001nT/°C over a range from-6°C to 21°C. For typical site separations of 10 to 15km throughout the San Andreas fault, estimates of σ for hourly mean data range from 0.15 to 0.3nT depending on local magnetization characteristics. Spectral density estimates indicate difference field noise power decreases with increasing frequency at about 3 db/octave. Dominant spectral peaks occur at diurnal harmonics and at the tidal M2 frequency. Geomagnetic difference-field noise limits measurement capability at all frequencies below about 2 c.p.h. Where instrument precision starts to limit detection capability, instruments of higher sensitivity may be useful.抄録全体を表示PDF形式でダウンロード (1197K) -
P. O. EZEMA, C. A. ONWUMECHILI1984 年 36 巻 3 号 p. 97-111
発行日: 1984年
公開日: 2010/09/14
ジャーナル フリーThe profile study involved the evaluation of the effect of the equatorial electrojet on magnetic variations for stations lying between geographic latitudes 14°N and 5°N or dip latitude 4°N and 8°S; and longitude 8°E. An attempt was made to use the strong non-uniform source field of the jet for day effects to make a sounding of average electrical conductivity as a function of depth. Results obtained from the analysis of data show consistency with FORBUSH and CASAVERDOE (1961) and with ONWUMECHILI and OGBUEHL (1967). A model based on the observed Sq shows that the depth of penetration is about 600km while a model based on the day time fast fluctuations shows that at periods of about one hour the depth of penetration lies between 400km and 600km.抄録全体を表示PDF形式でダウンロード (1026K) -
S. DUHAU, A. M. OSELLA1984 年 36 巻 3 号 p. 113-120
発行日: 1984年
公開日: 2010/09/14
ジャーナル フリーThe geomagnetic daily variations in Central Africa are separated into their parts of external and internal origin and from these parts the depth of the non-conducting layer in that zone is found using methods previously discussed by the authors. A sharp latitudinal gradient in this depth is found in the interval (-400km, 600km) around the dip equator.抄録全体を表示PDF形式でダウンロード (627K)
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