Correspondence between whistler mode ducts and chorus emissions observed on the Cluster spacecraft

Chorus emissions are intense naturally occurring plasma waves generated outside the plasmapause near the magnetic equatorial plane. Chorus often appears in two frequency bands, with an upper band above f_ce/2 and a lower band below f_ce/2, where f_ce denotes equatorial gyrofrequency. Bell et al. [2009] proposed that the source region for this configuration, known as banded chorus, consists of whistler mode ducts of depleted electron density for upper band chorus and ducts of either enhanced or depleted density for lower band chorus. This paper provides support for this model by showing that the requisite ducts generally exist near the magnetic equatorial plane. We also present two examples of banded chorus and discuss how these cases may be related to the duct structure.