In Situ Observations of Whistler‐Mode Chorus Waves Guided by Density Ducts

Abstract

AbstractIn this paper, we report the proof of the existence of density ducts in the Earth's magnetosphere by studying in situ observations of whistler‐mode chorus waves using NASA's Van Allen Probe‐A data. Chorus waves, originally excited inside the density ducts with wave normal angles (WNAs) smaller than the Gendrin angle at the near‐equatorial region, are efficiently confined to a limited area inside density ducts (i.e., ducted regions), and remain with small WNAs as they propagate toward higher latitudes. The ducted region becomes narrower for the higher‐frequency waves. Chorus waves with WNAs larger than the Gendrin angle are not guided by density ducts. Our study reveals that density ducts can effectively control the property and distribution of chorus waves, and may ultimately regulate electron dynamics in the Earth's or other planetary radiation belts.