Frequency‐Dependent Latitudinal Distributions of Plasmaspheric Plume Hiss Directionality and Amplitude

Abstract Plasmaspheric plume hiss plays a crucial role in shaping Earth's electron radiation belts and influencing magnetosphere–ionosphere energy coupling. However, its generation mechanism remains contested between cyclic‐linear and localized‐nonlinear models. By analyzing over 64,000 high‐resolution plume hiss wave segments from the Van Allen Probes (1 January 2013–31 July 2019), we identify a distinct frequency dependence in their latitudinal distributions of directionality and amplitude. For high‐frequency hiss, bidirectional propagation is sharply confined near the magnetic equator, beyond which poleward‐propagating waves overwhelmingly dominate, and the wave amplitude increases obviously with latitude. These signatures are consistent with a rapid, single‐pass, equatorially confined, nonlinear amplification process. In contrast, low‐frequency hiss exhibits a high prevalence and wide latitudinal extension of bidirectional propagation, with relatively smooth amplitude variations. This pattern supports a generation scenario involving slower growth, potentially linear or nonlinear, that is coupled with wave bounce motion along magnetic field lines.