Antisymmetric standing wave structure associated with the compressional Pc 5 pulsation of November 14, 1979

Abstract

Model calculations are performed to explain ion and electron flux pulsations observed at geostationary orbit in association with the compressional Pc 5 magnetic pulsation of November 14, 1979. The amplitude of the flux perturbation is calculated based on the observed value of the wave frequency, the azimuthal wave number, and the average distribution f(W, α) of the particles, for assumed forms of a standing wave structure along the ambient magnetic field. A theory developed by Southwood and Kivelson is followed to calculate the changes in energy and the location of the guiding center, which are experienced by particles in a given wave, and the consequential modulation of particle fluxes. It is found that if the compressional magnetic field component b∥ of the wave has a symmetric structure about the equator, net acceleration of the particles contributes significantly to the total amplitude of flux pulsations; whereas if b∥ has an antisymmetric structure, the total energy is conserved with the exchange of perpendicular and parallel energy leading to the modulation of the pitch angle distribution as the dominant cause of the flux pulsation. For the latter case, local magnetic field compression and the pitch angle dependence of the average particle distribution determine the amplitude of the flux pulsation. We find that antisymmetric models of b∥ reproduce the observations better than symmetric models. This result implies that there exists a class of compressional Pc 5 waves that do not have a fundamental standing wave structure.

Multispacecraft Cluster observations of quasiperiodic emissions close to the geomagnetic equator

“…We believe that this situation might be understood in terms of meridional oscillations of the node of the antisymmetric compressional wave [ Takahashi et al , ; Korotova et al , ]. If we assume the antisymmetric structure of the magnetic field [ Takahashi and Higbie , ], there is a node of the field‐line displacement located in the vicinity of the geomagnetic equator. However, the node is not stationary, but it oscillates with the wave.…”

On the drift magnetosonic waves in anisotropic low beta plasmas

“…Compressional waves are observed in magnetosphere 28,29 and in the magnetosheath of different planets. 30,31 Compressional waves found their applications in the nonlinear soliton like structure formation as the result of coupling of Alfv en and magnetosonic waves as investigated in the dawn flank of the magnetotail 32 and in electrons acceleration up to relativistic energies ($10 keV-few MeV) detected in the Van Allen radiation belts using data from cluster 3.…”

THEMIS observations of compressional poloidal pulsations in the dawnside magnetosphere: A case study

“…[6] Only a few observations of the nodal structure of Pc5 pulsations have been made and owing to insufficient spatial coverage of the data various standing wave models for Pc5 pulsations were suggested [Walker et al, 1982;Pokhotelov et al, 1985Pokhotelov et al, , 1986Takahashi and Higbie, 1986;Zhu and Kivelson, 1994]. Nagano and Araki [1983] performed a statistical study of the long-lasting compressional pulsations from GOES 3 (~5°N geomagnetic latitude) and GOES 2 (~10°N) to determine latitudinal wave properties and argued that the waves have a significant amplitude only near the equator.…”