On the correlation between Broad-Band ELF wave power and ion fluxes in the cusp

Abstract. We present a study of Broad-Band Extremely Low Frequency (BB-ELF) electric fields in the mid-altitude (4–6 Earth radii) cusp during periods of southward interplanetary magnetic field, using data from the Cluster spacecraft. Magnetospheric boundary layers are identified and classified according to particle precipitation characteristics. We find that the BB-ELF is contained within the cusp ion precipitation region, and its onset is closely co-located with the equatorward edge of the cusp ion dispersion signature. Previous studies have shown a positive correlation between BB-ELF and downward ion number flux. In this study, we compare the correlation coefficients of BB-ELF wave power versus the ion number and energy fluxes for upward, downward and total field-aligned fluxes. There is a greater degree of correlation between the total field-aligned flux and wave power than between the downward flux and wave power, which indicates that the BB-ELF wave generation is independent of ion beam direction. Our results support the idea of a local ion – BB-ELF wave interaction.