Hypotheses about long-period variations (i.e., seasonal, annual, and solar cycle) of geomagnetic pulsations have existed since the intensive research started. Nevertheless, insufficiently long data series prevented a conclusive and unambiguous detection of such variations. The Nagycenk observatory (Hungary) at an L value slightly below 2 has a pulsation time series including three solar cycles. Based on these data, period changes of Pc 3 pulsations are presented here, and an indirect connection with the yearly variation of the pulsation activity is supposed, both being due to changes of the magnetospheric plasma density. Longer periods of the pulsations around solar activity maxima should be due to higher particle concentrations at the respective shell of field lines, while 11-year average periods are influenced by long-term changes of the interplanetary magnetic field.
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