SOLAR-CYCLE EFFECT ON PC 3 GEOMAGNETIC-PULSATIONS

Hypotheses about long-period variations (i.e., seasonal, annual, and s olar cycle) of geomagnetic pulsations have existed since the intensive research started. Nevertheless, insufficiently long data series preve nted a conclusive and unambiguous detection of such variations. The Na gycenk observatory (Hungary) at an L value slightly below 2 has a puls ation time series including three solar cycles. Based on these data, p eriod changes of Pc 3 pulsations are presented here, and an indirect c onnection with the yearly variation of the pulsation activity is suppo sed, both being due to changes of the magnetospheric plasma density. L onger periods of the pulsations around solar activity maxima should be due to higher particle concentrations at the respective shell of fiel d lines, while 11-year average periods are influenced by long-term cha nges of the interplanetary magnetic field.