Complex Whistler-Mode Wave Features Created by a High Density Plasma Duct in the Magnetosphere

Abstract A Van Allen Probes observation of a high-density duct alongside whistler-mode wave activity shows several distinctive characteristics: (a) - within the duct, the wave normal angles (WNA) are close to zero and the waves have relatively large amplitudes, this is expected from the classic conceptualization of ducts. (b) - at L-shells higher than the duct’s location a large “shadow” is present over an extended region that is larger than the duct itself, and (c) - the WNA on the earthward edge of the duct is considerably higher than expected. Using ray-tracing simulations it is shown that rays fall into three categories: (i) ducted (trapped and amplified), (ii) reflected (scattered to resonance cone and damped), and (iii) free (non-ducted). The combined macroscopic effect of all these ray trajectories reproduce every feature in the spacecraft observation.