Abstract
The observed anticorrelation between the 11-year solar activity cycle and the appearance of Pc 1 geomagnetic pulsations as well as the resonance structure of the electromagnetic noise spectrum (SRS) in the frequency range 0.1–10 Hz is explained on the basis of the role of the ionospheric Alfvén resonator (IAR) in the formation of both phenomena. The reflection coefficient R of Alfvén waves from the IAR determines the threshold of the cyclotron instability (CI) which is the cause of Pc 1 pulsations. At the same time, the quality of the IAR, which varies synchronously with R, controls the SRS modulation depth. It is shown that the decrease of the maximum value of |R| during the maximum phase of the solar activity cycle remarkably increases the CI threshold and sharply decreases the modulation depth of SRS, thus decreasing the occurrence probability of both phenomena.
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