The relations between magnetospheric chorus and hiss inside and outside the plasmasphere boundary layer: Cluster observation

Magnetospheric whistler mode emissions (chorus and hiss) can play an important role in acceleration and loss of energetic electrons by wave‐particle interaction. Here we present a first report of two events in the simultaneous observations of chorus and hiss by the Cluster constellation. During the event of 30 August 2001, one spacecraft observed chorus in the plasmasphere boundary layer (PBL), and three spacecraft observed hiss in the plasmasphere. In the event of 18 November 2002, one Cluster spacecraft observed hiss inside the plasmasphere, and the other three spacecraft observed chorus outside the plasmasphere. The correlation between chorus and hiss waves in both events are analyzed via intensity comparison and cross‐correlation analysis. It is found that chorus and hiss waves have significant correlation in the first event but have no correlation in the second event. Furthermore, we perform a ray‐tracing study to investigate the correlation by adopting two typical density models: the MTotal density model associated with the PBL structure and the global core density model. Simulation results demonstrate that chorus waves outside the plasmapause can propagate into the plasmasphere and possibly evolve into hiss waves under the MTotal density model, supporting the previous finding that the plasmaspheric hiss may originate from discrete chorus emission. However, chorus cannot travel into the plasmasphere under the global core density model. This paper presents a first result that chorus has more opportunity to propagate into the plasmasphere through the PBL than through the plasmapause. The results suggest that the gradual density variation of the PBL appears to favor the inward propagation of whistler mode waves.