Field-aligned structure of the storm time Pc 5 wave of November 14–15, 1979


  • K. Takahashi,

  • J. F. Fennell,

  • E. Amata,

  • P. R. Higbie


Magnetic field data from the four satellites SCATHA (P78-2), GOES 2, GOES 3, and GEOS 2 have been analyzed to examine the magnetic field-aligned structure of a storm time Pc 5 wave that occurred on November 14–15, 1979. The wave had both transverse and compressional components. At a given instance the compressional and the radial components oscillated in phase or 180° out of phase, and the compressional and the azimuthal components oscillated +90° or −90° out of phase. In addition, each component changed its amplitude with magnetic latitude: the compressional component had a minimum at the magnetic equator, whereas the transverse components had a maximum at the equator and minima several degrees off the equator. A 180° relative phase switching among the components occurred across the latitudes of amplitude minima. From these observations the field line displacement of the wave is confirmed to have an antisymmetric standing structure about the magnetic equator with a parallel wave length of a few earth radii. We also observed other intriguing properties of the wave such as different parallel wave lengths of different field components and small-amplitude second harmonics near the nodes. A dielectric tensor appropriate for the ring current plasma is found to give an explanation for the relation between the polarization and the propagation of the wave. However, plasma data available from SCATHA does not support either the drift mirror instability of A. Hasegawa (1969) or the coupling between a drift mirror wave and a shear Alfvén wave as discussed by A. D. M. Walker et al. (1982).