Multipoint observations of spatial and temporal characteristics of Pc 4-5 pulsations in the dayside magnetosphere and particle signatures.

Abstract

<p>We use  multipoint magnetic field, plasma  and particle observations to study the spatial, temporal  and spectral characteristics of Pc 4-5 pulsations   observed  in the recovery phase of a strong magnetic storm on January 1, 2016.   The magnetosphere was compressed and periodic increases of the total magnetic field strength occurred every 20-40 min at the times of generation of the pulsations.  The frequencies of the Pc4 pulsations varied  from 14 mHz to 25 mHz with radial distance. An explanation for this behavior can be given in terms of standing Alfvén waves along resonant field lines.  By contrast, Fourier analysis of the magnetic field observations  shows that the compressional  Pc5 pulsations  exhibited  similar spectra at different radial distances.  The long duration of the Pc5 pulsations and their nearly constant frequencies indicate that the plasma conditions in the morning sector of magnetosphere were stable for more than two hours.  The Pc4 and Pc5   pulsations displayed wave properties consistent with the second harmonic waves. The energetic particles   observed by Van Allen Probes and GOES 15  exhibited  a 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.   We searched for possible solar wind triggers and discussed generation mechanisms for the compressional Pc5 pulsations  in terms of drift mirror instability and  drift bounce resonance. </p>