Problems of the Pc1 magnetospheric wave theory. A review

The Pc1 ultralow-frequency electromagnetic waves (frequency range 0.2–5 Hz), also known as pearl necklace, are a unique phenomenon in near-Earth space physics. Many properties of pearls remain a mystery, despite the research of prominent cosmophysicists for more than half a century. In the proposed review, we briefly outline the main points of the so-called standard model, which is widely used to interpret Pc1. Next, we focus on the criticism of the standard model and on the identification of open problems in the Pc1 theory. The general conclusion is that it is necessary to develop new ideas outside the framework of the standard model in order to understand the processes of excitation and propagation of Pc1 waves in Earth’s magnetosphere.