Speaker
Description
Whistler-mode waves are commonly observed in magnetized plasma environments, such as Earth’s inner magnetosphere, where wave-particle interactions play a significant role in radiation belt electron dynamics during geomagnetically active periods. Several mechanisms have been proposed for the generation of whistler-mode waves within the dense plasmasphere and plasmaspheric plumes, including local generation by anisotropic electron injection, penetration of chorus emissions from the outer zone, and nonlinear wave growth. This study investigates the generation and propagation characteristics of whistler-mode emissions during a series of plume-crossing events observed by the Van Allen Probes during an ICME-driven geomagnetic storm from April 9 to 12, 2015. The relative positioning of the probes enabled a comparative analysis of wave activity in regions with different plasma densities. Energy flux analyses from both spacecraft, simultaneously located inside and outside plume structures, indicate that the propagation of chorus waves across the plume boundary often precedes the appearance of large-amplitude plume hiss emissions. Rising-tone chorus-like waves are also observed within the plume, suggesting a contribution from nonlinear growth processes. Notably, changes in the direction of wave energy propagation are observed between plume and plasmathrough regions, with inward-directed flux in the plasmathrough between two high-density regions potentially facilitating energy transfer into the plasmasphere. Additionally, the occurrence of exohiss near the plumes shows a correlation with anisotropic electron populations, indicating local generation. These findings contribute to a deeper understanding of the relative role of different generation mechanisms and propagation of whistler-mode waves under varying plasma conditions.
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