The Effect of an Ocean on Magnetic Diurnal Variations

Roden, Robert B.

doi:10.1111/j.1365-246x.1964.tb03859.x

Cited by 54 publications

(20 citation statements)

References 10 publications

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“…On the other hand, it has sometimes been pointed out that the geomagnetic variation anomalies in Japan might be due to the effects of the sea surrounding Japan (e. g., RODEN, 1964). According to RIKITAKE (1961) and RIKITAKE and SASAI (1969), it seems unlikely, however, that the anomalies in Japan are accounted for by the effects of the sea only.…”

Section: Introductionmentioning

confidence: 96%

Electrical conductivity anomalies beneath the Japan arc.

Honkura

1974

J. geomagn. geoelec

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As a result of intensive observations of geomagnetic variations over many years, the overall distribution of anomalous Z fields has become clear in Japan. One of the anomalies, the central Japan anomaly, has been accounted for by a depression of a highly conducting layer in the mantle beneath Japan, although the effect of the sea on the anomaly has not been brought out quite clearly. The period dependence of the anomalies along lines across central and northeastern Japan is examined by making use of the transfer function technique. Anomalous Z fields can be traced on a few islands in the Pacific Ocean south of central Japan, although they are strongly contaminated by island effects there. It is found out that the central Japan anomaly has a strong period dependence. The anomaly along the line across northeastern Japan also has a strong period dependence which is slightly different in its characteristics from that for the central Japan anomaly. Numerical calculations of electromagnetic induction based on the method given by JONES and PASCOE (1971), have been made for two-dimensional models, and the calculated transfer functions are compared with the observed ones. As a result, it is found out that the sea surrounding the Japan Islands plays an important role on both the anomalies. The anomaly in the central part of Japan, however, cannot be accounted for by the sea only. On the basis of these calculations, possible electrical conductivity models beneath the central and northeastern parts of Japan are put forward. It is concluded that a highly conducting layer seems likely to lie at a depth of 30km beneath the Philippine Sea and the Japan Sea. Anomalous Z fields associated with ssc's, geomagnetic bays and similar changes have been found on Oshima, Miyake-jima and Hachijo-jima Islands. Such an island effect is certainly caused by the induced electric currents which are distorted by the low conductivity of the island. However, the calculated effect does not agree with the observed one when electromagnetic coupling between the sea and the conducting layer in the mantle is ignored. A detailed study of electromagnetic coupling suggests that a highly conducting layer lies close to the earth's surface beneath the northern part of the Izu-Bonin arc.

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Section: Introductionmentioning

confidence: 96%

Electrical conductivity anomalies beneath the Japan arc.

Honkura

1974

J. geomagn. geoelec

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“…Calculations of Ashour [1971b] as well as model experiments of Roden [1964] indicate that possibility 1 is capable of generating a su•ciently large Z/H. However, both of these tend to exaggerate the induced currents because of the abnormally high vertical component of the primary field.…”

Section: B Local Modelsmentioning

confidence: 99%

“…This is understandable considering the decrease in vertical component caused by the image currents. One of the first applications of scale models to electromagnetic induction was an attempt byRoden [1964] to account for the Japanese anomaly. He used a purely vertical primary field, no conductosphere, and a fiat earth approximation.…”

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confidence: 99%

The geomagnetic coast effect

Parkinson¹,

Jones²

1979

Reviews of Geophysics

121

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“…RIKITAKE (1964), who, along with his co-workers has studied geomagnetic variations in Japan in considerable detail, suggested in a short note presented to the IUGG Symposium on the Upper Mantle Project at Berkeley in 1963 that the major cause of the anomalous behaviour of the vertical magnetic field component near the Japanese coast is the complicated mantle structure beneath Japan. RODEN (1964) studied the effect of the Pacific Ocean on magnetic variations in Japan by the use of an analogue model and theoretical calculations and felt that the mantle structure is not the only cause of the anomalous effects, but there is some contribution due to currents induced in the ocean By using seismic and magnetic data, LAMBERT and CANER (1965) investigated the mantle structure beneath the British Columbia coastline. Also, Dosso (1966) has used analogue models of different coastal structures and examined the behaviour of the phases and amplitudes of the surface E and H components.…”

Section: Introductionmentioning

confidence: 99%

Investigation of the Coastal Effect by Three Numerical Models

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Ainslie

Jones

1973

J. geomagn. geoelec

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The geomagnetic effects of a coastline are investigated for the E polarization case. Calculations of the amplitudes and phases of the surface electric and magnetic field components are given for three different two-dimensional models. The calculated values for these models show the effects of electric currents in the ocean and in the mantle. Two different frequencies of the sinusoidally time varying fields are used, and so skin effects are also shown in the results. The results show the similarity of a coastal effect due to the ocean alone and a coastal effect due to the ocean and mantle.

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The Effect of an Ocean on Magnetic Diurnal Variations

Cited by 54 publications

References 10 publications

Electrical conductivity anomalies beneath the Japan arc.

Electrical conductivity anomalies beneath the Japan arc.

The geomagnetic coast effect

Investigation of the Coastal Effect by Three Numerical Models

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