Novel EMIC Wave Propagation Pathway Through Buchsbaum Resonance and Inter-Hemispheric Wave Interference: Swarm Observations and Modeling

In situ conjugate electromagnetic ion cyclotron (EMIC) waves observed by the Swarm mission in both hemispheres are presented. A complex and unusual pattern of Alfvenic EMIC wave energy is observed, with a mid-latitude peak close to the source at L =3.3, as well as a secondary lower L-peak. A wave propagation model reveals that the secondary peak at L =1.7 may be explained by wave power being redirected equatorward due to the Buchsbaum resonance, crossing and interfering with the same EMIC wave power propagating equatorwards from the opposite hemisphere. This interference creates a coherent equatorial driver for a low-L field line resonance at the secondary peak, and which is associated with strong shear-to-fast mode coupling in the ionosphere. This behavior complicates the interpretation of low-Earth orbit EMIC data for applications assessing radiation belt loss. Combined low Earth orbit observations and modeling enable these novel and localized magnetosphere-ionosphere EMIC wave propagation pathways to be identified.