A study is presented of the D-region winter anomaly, observed by ground based measurements of long-distance VLF radio wave propagation and HF radio wave vertical sounding at several stations located in and near Japan over 3 winters from 1974 to 1977. These winters have different meteorological conditions (i. e., a mayor stratospheric sudden warming in the winter 1976/77, a minor warming in 1974/75 and no warmings in 1975/76). The activity of the anomaly is compared with that of planetary-scale waves using atmospheric data in the lower stratosphere and radiance data in the upper stratosphere and mesosphere obtained by the PMR (Pressure Modulator Radiometer) on board Nimbus 6 satellite. The latitudinal extent and duration of the anomaly are shown to be primarily controlled by the amplification of planetary-scale wave with zonal wavenumber 1. When a major warming took place as a result of an unusual amplification of wave 1, an intense event of the anomaly was observed for a long time. However, the low-latitude boundary was high (≥40°N). The situation was similar with the case of minor warming except that the low-latitude boundary was normal (-35°N). When the wave 1 was amplified but no warmings were observed, relatively weak events of the anomaly occurred. The duration was dependent on the wave 1 activity but generally short. The low-latitude boundary became low in latitude (-30°N) with the wave 1 activity. It is further demonstrated that a localized temperature increase excited by the vertical propagation of wave 1 into the mesosphere has a close relation to the enhancement of electron density in the D-region during winter anomalous days. This suggests that the decrease of effective electron recombination coefficient due to the temperature increase is a primary cause of the winter anomaly.

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An expression for the field induced by the ionospheric current system at equatorial latitudes, due to the presence of a mantle with a non-uniform boundary in the north-south direction was obtained using conformal mapping. The induced field was then calculated for the particular case of a semi-elliptical rise of the mantle, and the result applied to the equatorial zone of Peru, where a latitudinal gradient in the depth of the non-conducting layer had been found in previous work. Finally, the results were correlated with the tectonic features of the studied zone.

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In 1981 and 1982 intensive observations of the geomagnetic field were carried out in a possible seismic gap region in the western part of the North Anatolian Fault Zone to trace on active fault and also to accumulate geomagnetic data for earthquake prediction research. The data of magnetic anomalies obtained from profile measurements across the fault were interpreted to reveal an anomalous magnetic structure associated with the active fault. In order to confirm our results thus derived in the Iznik-Mekece area, similar observations were also made at Ismetpasa where fault traces are well known as well as creep for the North Anatolian Fault Zone.
It is concluded that highly magnetized dike-like bodies exist extensively along active fault lines in the North Anatolian Fault Zone. This characteristic feature can be utilized for studies of active fault location and also for tectonomagnetic studies.

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A change in the declination of magnetization with plate rotation has been quantitatively estimated. This effect should be taken into consideration in discussing the tectonic rotation of a given region in paleomagnetism. Unless there has been tectonic rotation of the region we can determine the “paleolongitude” from this calculation. An attempt to determine the “paleolongitude” has been made in the case of Chichijima in the Bonin islands. In comparison with the declination calculated from the geomagnetic anomalies on Chichijima, we discuss the possibility that the Bonin islands have drifted from the Pacific Ocean.

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