Multispacecraft Observations of Pc 4 -5 Pulsations in the Dayside Magnetosphere: Particle Signatures.

We use magnetic field, plasma, and particle observations from multiple locations to study the spatial, temporal, and spectral characteristics of Pc4-5 pulsations observed after a strong magnetic storm. The region where the Pc4-5 pulsations were generated occupied a wide longitudinal region in the dayside magnetosphere. Near noon their peak to peak amplitudes reached 16 nT in the compressional component. The magnetic field spectra calculated from Van Allen Probes showed that magnetospheric plasma conditions were stable for more than two hours. We investigated wave modes and their nodal structure. We demonstrate that when the magnetic field waves had a strong compressional component, the spacecraft observed meridional sloshing of the node that was confined in latitude between 0.23 Re and -0.8 Re and its amplitude did not exceed 0.5 Re. Clear signatures of this meridional sloshing of the node were seen in the fluxes of electrons and electron density observed by MagEIS and HOPE, respectively. The particles observed by the Van Allen Probes exhibited regular periodicity over a broad range of energies from tens of eV to 2 MeV with periods corresponding to those of the compressional component of the ULF magnetic field waves, and the electron and proton fluxes and the magnetic field oscillated out of phase. We discuss possible mechanisms of generation of Pc 4 -5 pulsations in terms of drift mirror instability and drift bounce resonance.