抄録
The irregular pulsations of Pi2 class are reported to contain most often pulsations of shorter periods in the range of Pils, probably forming the fine structure of Pi2 pulsations. The properties of such short period pulsations are studied utilizing the data obtained during 1967-74 at Choutuppal (geomagnetic latitude: 7°28′N), India. The study reveals a clear influence of background magnetic activity on the occurrence of shorter period components, an appreciable seasonal dependence of fine structure activity and a systematic change in the nature of this dependence during the course of a Solar Cycle, in that the equinoxial season predominates in the fine structure activity during years around sunspot maximum, while during years away from solar maximum the activity is more pronounced during winter season. The period distribution of short period activity from a detailed power spectral analysis revealed clear peaks around 5.5, 11.0, and 16.5sec. It is suggested that at least part of the equatorial Pi2 fine structure, particularly the signals with periods around 10.0sec and more be viewed as due to resonance of innermost cavity of magnetosphere, triggered by the impulsive disturbances generated at the boundary or outside of the magnetosphere.
