Studies on the Disturbances in F2 Layer Associated with Geomagnetic Disturbances

抄録

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.