A close relation between Ionospheric absorption of cosmic radio noise and chorus intensity at the auroral zone is found for diurnal variations of them on geomagnetically 5 quiet days, those on geomagnetically 5 disturbed days, and storm-time variations of them using the data at College, Alaska for periods of no polar-cap absorption from September, 1959 to December, 1960. Then we discuss the relation of the cosmic noise absorption to the chorus and to geomagnetic pulsation at the auroral zone, and do also possible mechanisms of VLF emissions in the outer exosphere.

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The relation of low-energy solar cosmic ray events to the type IV solar radio outbursts is examined statistically, using the data obtained during the IGY (1957-1958) and the IGC (1959). The solar radio emission data include those at frequencies 167, 200, 500, 1000, 3000 and 9500Mc/s. With respect to the sun-earth transit time of those cosmic rays, it is found that there are two types, viz., F type (Fast type) and S type (Slow type), their transit time being shorter in F type particles than in S type particles. These two types (F and S types) correspond to the different characteristics of type IV outbursts spectra. It is found that the intense emission in the centimeter-wave region of type IV outbursts is closely related to the generation of solar cosmic rays. The mechanisms of their acceleration in the solar atmosphere and their propagation in relation to type IV outbursts are also examined.

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The rate of energy penetration of VLF (10Kc) radio waves through a sharp ionospheric boundary under a constant magnetic field is calculated and the directions of the ray and the wave normal at the boundary are discussed.
For the case in which the VLF radio waves go up into the ionosphere from free space below, a rigorous calculation is performed using Bremmer's method and the existence of a quasi-Brewster's angle is ascertained.
In the case in which the waves come downwards from above, an approximate method is set up for the calculation and it is shown that the VLF waves can penetrate down to the earth's surface, only when the wave normal lies in a narrow band of angle near the normal of the boundary. In this case the ray direction of the penetrating waves is close to the magnetic field.

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