An explanation of anomalous variations of the maximum electron density (proportinal to (f₀F2)²) and its height (h_pF2) of the F2 region is attempted. For this purpose, the reexamination of the behaviours of f₀F2, h_pF2 and h′F2 in three seasons during sunspot maximum and minimum, is made and some interesting results are obtained. They are the followings. (i) The geomagnetic control of f₀F2 is conspicuous in low and middle latitudes in there seasons. But above middle latitudes the geographic control is remarkable. This is applied above 30° in winter (greatest secχ) and equinox. (ii) f₀F2 above 20° in December distributes approximately in such a way as f₀F2∝cos^1/2χ during sunspot minimum, but its distribution during sunspot maximum deviates from this line. (iii) The greater the zenith angle, the greater the increase of electron density from s. s. min. to s. s. max., and thus the magnitude of the seasonal anomaly of f₀F2 is amplified far more during sunspot maximum than the minimum (iv) The value of h_pF2 is greatest at geomagnetic equator throughout the year. (v) h_pF2 becomes larger during sunspot maximum than the minimum. (vi) h_pF2 in December does not increase at higher latitudes and rather decreases.
From these facts it seems that the variations of f₀F2 and h_pF2 are controlled not only by the geomagnetic cause, but also by the cause which relates to the geographic latitude or solar activity. We investingate the geomagnetic distortion of daily variation of electron density due to the vertical electron drift, taking the diurnal and semi-durnal components into consideration, and show that the trough in geomagnetic equator can be explained by this drift. The velocities of two kinds of drift are deduced directly from the data. A reason for geographic control is described. It is shown that the seasonal anomaly of f₀F2 cannot be accounted for only by the vertical drift. Therefore in order to explain the seasonal anomaly of f₀F2 and other phenomena, (iii)-(iv), mentioned above, we suggest that there is at least the seasonal variation of the height distribution of the particle responsible for the F2 region.

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The existence of some correlation between the geomagnetic storm and the ionospheric F2 layer disturbance has long been investigated since the early stages of ionospheric researches. Recenty, this problem has been studied by many investigators not only from geophysical interest but also under the necessity of improving radio communications.
The main course of investigation on F2 disturbance, which has been studied by the author for the last three years, is summarized as follows:
(1) The separation of variations in f⁰F2 and h′F2 associated with geomagnetic storms into two parts depending on the universal time and local time, the so-called Dst(F2) and S_D(F2), respectively, was clarified.
(2) The devlopment process of the F2 disturbance was investigated in respect to each of D_st(F2) and S_D(F2). It is concluded that S_D(f⁰F2) exists in the earlier stage of geomagnetic storm and D_st(f⁰F2) grows in the comparatively later stage.
(3) The latitudinal and seasonal characteristics were shown.
(4) Investigations were made in the behaviour of the F2 layer according to the different levels of geomagnetic activities. Results showed that the F2 layer disturbance was generally in proportion to the geomagnetic activities, except for D_st(f⁰F2) variation in winter.
(5) As to the successive yearly variation of, ionospheric disturbance, it was found that the phase of S_D(F2) would lag behind according to the decrease of sunspot activity.

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The direct relation between the geomagnetic S_q variation and the vertical electron drift in the F2 region on the magnetic equator is examined.
It is shown that the electric field in the F2 region accompanied by S_q electric current produces the vertical drift which is sufficient to interpret the main features of the anomaly of the F2 region on the equator. It is to be noticed that the main term of the drift velocity is diurnal. The daily variations of the maximum electron density and its height in the F2 region are calculated under consideration of the vertical electron drift for the reasonable distribution of decay coefficient with altitude inferred by observed results. The calculated F2 daily variations have a striking resemblance with those observed near the magnetic equator. When the ion production takes its maximum value at about 200km, there appears a lower secondary maximum of electron density which agrees well with the observed F1 layer.
The change of characteristics of daily variations of the F2 region with the sunspot-cycle is likely to be accounted for by a slight shift of the phase of the drift.

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The early Pleistocene basaltic lavas at Kawajiri-misaki (Cape Kawajiri) have in general reverse natural remanent magnetism (N. R. M.), while at a part of the place both specimens of reverse and normal N. R. M. are found with their positions as intermixed, despite that they have been taken from the same rock block, and with their intensities ranging from 10^-4 to 10^-2c. g. s. e. m. u./g. This fact seems to suggest that there is much room for the discussion regarding the idea that the reverse N. R. M. of the lavas would have been caused by a reverse geomagnetic field assumed to have occurred at the age of the ejection of the lavas.

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