Problems of physics of Pc1 geomagnetic pulsations: On the 90th anniversary of discovery of pearls

“Pearl necklaces”, or simply “pearls”, are undoubtedly the true adomment of the rich diversity of ultra-low-frequency electromagnetic waves in Earth’s magnetosphere. They are noted for outstanding beauty of their form and the mystery of their origin. Pearls were first observed by E. Sucksdorff and L. Harang in 1936. This article celebrates the anniversary of their discovery. It briefly outlines the so-called standard model of pearl excitation and propagation. The key importance of the standard model’s fundamental principles in planning research and interpreting the results obtained is emphasized. We point out difficulties with the standard model, particularly the deviation from antisymmetry in the appearance of pearls at conjugate points. An alternative model is proposed which is based on the concept of an ion-cyclotron resonator located in the equatorial zone of the outer radiation belt. It is hypothesized that the excitation of a discrete sequence of pearls is caused by ponderomotive self-Q-modulation of the ion-cyclotron resonator.