Some features of Pc5 pulsations during a solar cycle

The morphological features of Pc5 pulsations during a solar cycle are studied using Fort Churchill data for the years 1962 to 1972. Some of the characteristics noted are as follows: (1) Increasing sunspot numbers show little influence on the diurnal variations of the occurrence, amplitude and the period except perhaps some noticeable change in the absolute magnitude of these parameters during different hours of the day. (2) The morning occurrence peak dominates during all phases of the solar cycle. (3) With increasing magnetic activity the day side region(s) of generation of Pc5 is found to shift closer to the subsolar point and in the midnight sector, the occurrence region seemed to shift towards earlier hours with increasing magnetic activity and towards later hours with increasing sunspot numbers. (4) The amplitude of Pc5 pulsations is directly related to all the levels of magnetic activity. (5) The periods of Pc5 pulsations show strong correlation with increasing sunspot numbers and the amplitude and occurrences are found to vary in accordance with the magnetic activity all through the cycle. (6) The annual and semi-annual variations of Pc5 parameters have been demonstrated especially for the pulsations occurring in the morning close to 8 +- 1 h LT and for those occurring near the midnight hours. (7) a suspected 27-day recurrence tendency has been clearly noticed for the occurrence, amplitude and period of Pc5 pulsations. (author)