Solar cycle effects on geomagnetic Pi 2 pulsations

Rapid-run magnetograms of more than 6000 Pi 2 events generally associated with bay disturbances observed at Onagawa, Japan, and Fredericksburg, Virginia, during the years from 1956 through 1966 were analyzed to search for solar cycle effects. Yearly occurrence frequency of the Pi 2's including not only large amplitudes but also medium and small ones showed an inverse relation with solar activity. The local time of the maximum occurrence of Pi 2 changed from year to year between 22 h and 01 h LT. The daily occurrence frequency of Pi 2 seemed to have a systematic recurrence tendency caused by the solar rotation. The Pi 2 period decreased from 1957 to 1960 and increased from 1962 to 1965, depending on the magnitude of the accompanying bay disturbance. In relation to these solar cycle variations of Pi 2, an occurrence mechanism of magnetic field oscillations at the time of Pi 2 events is discussed based on the data at 14 world-distributed stations.