The effect of IMF Y-component in GSE coordinate system on the low latitude horizontal intensity has been studied in detail. The relation between B_y and H is found to vary with time of the day, season and polarity of the IMF component.

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Phase anomalies of VLF radio waves were investigated in relation to geomagnetic disturbances, using data obtained from the reception of the NLK station during 37 months from August 1970 to December 1974. The horizontal component of geomagnetic field observed at Memambetsu (Japan) together with the Ap index is used as an index of intensity of a geomagnetic disturbance. Primary storm effects on the phase anomalies during nighttime with an average value of 8μsec have a tendency to occur 2 hours later than the decrease of horizontal component of geomagnetic field with an average value of 70 gammas (hourly mean value). Storm after-effects which are the main features at midlatitudes continue for 3 days with large phase anomalies and further continue for about 5 days with small ones. Phase anomalies were observed during the daytime when the solar zenith angle was about 70° and observed during severe storm periods even with a solar zenith angle of 30°. Sudden phase anomalies were observed just after magnetic Pi pulsations.

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An analysis of absolute mean hourly values of the three geomagnetic elements H, D and Z at Alibag for the period 1932-1972 has revealed clear and significant L (O₁), the geomagnetic lunar daily variation associated with the lunar atmospheric tide O₁. Partial tides are small in comparison with the phase law tides, suggesting that the variation resulting from the atmospheric tide O₁ and higher harmonics of ionospheric conductivity contribute little to L (O₁) at Alibag. Separation of L (O₁) into parts of oceanic and ionospheric origin shows that (i) primary source of L (O₁) in Z is the oceanic dynamo; (ii) smaller amplitude of the first harmonic of L (O₁) compared to that of the second, contrary to expectation, is not due to the influence of oceanic dynamo contribution on L (O₁). It is inferred that even yearly L (O₁) contains some contribution from L (M₂), lunar variation associated with the atmospheric tide M₂. Next, by applying the formulae due to Winch, the seasonal harmonics of L (O₁) and L (M₂) are corrected for the possible contamination of one by the other. It is found that seasonal progression of L (O₁) and L (M₂) prior to and after the removal of the effect of one from the other remains the same.

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The occurrence of the afternoon counter-electrojet events has been investigated from extensive data of the equatorial station at Trivandrum over a period of 19 years. Seasonal variation reveals a hitherto unreported secondary occurrence peak in January, in which month a disproportionately large number of strong counter-electrojet events is noticed. The peak of the occurrence follows the minimum in sunspot activity by an interval of a little over one year. When the occurrence is examined separately for days of A (Away) and C (Toward) polarities of the Interplanetary Magnetic Field, it is noticed that the peak occurrence in local summer, observed for these events, shifts towards the vernal equinox for the A-sector events; for C-sector events there is a suggestion of a shift of the peak from summer towards the autumnal equinox.

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One hundred and twenty-five (125) oriented samples (286 specimens) were obtained from thirty-three (33) sites in metavolcanic rocks and diabase dyke swarms from the ophiolite complex of Thetford Mines in the Appalachians of Southern Quebec (longitude: 71°00′-71°45′W, latitude: 45°45′-46°15′N). The metavolcanic rocks are massive or pillowed (mainly) lavas of andesitic and mostly basaltic composition and the dyke swarms are composed of basaltic and doleritic diabases; both lithological groups are metamorphosed to the subgreenschist (pumpellyite) facies. Pyroclastics, tuffs and volcanic agglomerates are also present in minor quantities.
The NRM intensities of the metalavas and diabases are very weak. Magnetic, titanomagnetite and occasional grains of hematite are the magnetic memory carriers. Native iron was also detected in minute quantities. In order to obtain some pertinent information relative to the stability of the NRM component, stepwise alternating field (AF) demagnetization was conducted on 30% of the specimens in the 50-800 Oersteds range and the others were demagnetized at an optimum AF intensity. Approximately 10% of the specimens underwent thermal treatment in the 100-550°C range; thermal demagnetization was judged less efficient than AF demagnetization and for this reason, the remaining specimens were all AF demagnetized.
After AF treatment, the paleopole position of the tilted ophiolite complex is 206° to 09°S (d_m=16°, d_p=10°, K=61), i. e. 26°E, 09°N (normal polarity).
Petrological and magnetic studies of the ophiolite complex of Thetford Mines indicate that the basaltic and doleritic diabase dykes which feed the overlying pillow lavas in the Thetford Mines complex have NRM intensities and Koenigsberger ratios which are comparable to those of the layer of pillow lavas. As the NRM intensities of both the pillow lavas and the diabase dyke swarms are low, they ought to be relatively unimportant contributors to magnetic anomalies. The large NRM intensities and Koenigsberger ratios of the gabbroic layer and particularly the harzburgite, dunite, wehrlite and pyroxenite of Thetford Mines suggest that the ultramafic layers are the most significant magnetic sources which might well explain the younger marine anomalies. Surface alteration and low temperature oxidation may, however, be partly responsible for the low NRM intensities of the relatively thin (1km-thick) layer of pillow basalts of this ancient sea floor.
The absence of a reliable model of the source(s) of the magnetic lineations is a serious handicap in the solution of numerous geological and geophysical problems such as dyke intrusion models of seafloor spreading geomagnetic reversal time-scale and paleogeographic reconstruction (BANERJEE et al., 1974). This study is concentrated on these two last aspects.

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The behaviour of the time-varying electromagnetic fields over the Vancouver Island region is investigated using a scaled analogue model. The results show that conductive channelling in the shallow seawater channel around the island is important for both E and H polarization of the inducing field and for all frequencies studied. It appears that channelled telluric currents flow along either side of Vancouver Island with some diffusion of current into the continent to the southeast of the island. For the H polarization case there is some evidence of current flow around the SE tip of Vancouver Island as well. The results also show the effects of local confinement of current whereby the direction of telluric flow is modified by the geometry of the seawater channel.

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