An investigation into the spectral parameters of ultra-low-frequency (ULF) waves in the polar caps and magnetotail

The present case study is focused on fluctuations at similar to 1.5 mHz observed on open field lines in both of the polar caps in ground-based geomagnetic data and in the electron concentration in the Northern Hemisphere ionosphere. Coherent pulsations with a relatively narrow narrowband-like spectra and a higher fraction of transversal components in the total spectral power are also observed by the Cluster satellites in the magnetotail magnetic field. Interestingly, the pulsations in the magnetotail started after pulsations over a similar frequency range observed in the solar wind dynamic pressure and interplanetary magnetic field (IMF) had been switched off. This suggests evidence of an internal resonant magnetotail mode which is normally masked by a higher-amplitude broadband ultra-low-frequency (ULF) "noise" of extra-magnetospheric origin.