The significant role of nonlinear wave–particle interactions in the macrodynamics and microdynamics of the Earth’s outer radiation belt has long been recognised. Electron dropouts during magnetic storms, microbursts in atmospheric electron precipitation, and pulsating auroras are all associated with the rapid scattering of energetic electrons by the whistler-mode chorus, a structured electromagnetic emission known to reach amplitudes of about \(1\%\) of the ambient magnetic field. Despite the decades of experimental and theoretical investigations of chorus and the recent progress achieved through numerical simulations, there is no definitive theory of the chorus formation mechanism, not even in the simple case of parallel (one-dimensional) propagation. Here we follow the evolution of these theories from their beginnings in the 1960s to the current state, including newly emerging self-consistent excitation models. A critical review of the unique features of each approach is provided, taking into account the most recent spacecraft observations of the fine structure of chorus. Conflicting interpretations of the role of resonant electron current and magnetic field inhomogeneity are discussed. We also discuss the interplay between nonlinear growth and microscale propagation effects and identify future theoretical and observational challenges stemming from the two-dimensional aspects of chorus propagation.

非线性波粒相互作用在地球外辐射带的宏观动力学和微观动力学中的重要作用早已得到认可。磁暴期间的电子丢失、大气电子沉淀中的微爆和脉动极光都与高能电子通过哨子模式合唱的快速散射有关，这是一种结构化的电磁发射，已知其振幅约为 \(1\%\ )的环境磁场。尽管对合唱进行了数十年的实验和理论研究，并且最近通过数值模拟取得了进展，但尚无关于合唱形成机制的明确理论，即使是在平行（一维）传播的简单情况下也是如此。在这里，我们跟踪这些理论从 1960 年代开始到现在的演变，包括新出现的自洽激发模型。考虑到最近航天器对合唱精细结构的观测，对每种方法的独特特征进行了批判性审查。讨论了对共振电子流和磁场不均匀性作用的相互矛盾的解释。