TY - JOUR

T1 - Phase-mixing poloidal alfvén wave polarisations

AU - Mann, I. R.

AU - Wright, A. N.

AU - Hood, A. W.

PY - 1997

Y1 - 1997

N2 - Standing poloidal Alfvén waves are believed to be excited by
drift-bounce resonance with energetic particle populations in the
Earth's magnetosphere. Using a fully compressible ideal MHD model, in a
cartesian geometry, we investigate the temporal evolution of localised
poloidal Alfvén waves evolving in radially inhomogeneous
magnetoplasmas. We find that the polarisation of these waves rotates
from being poloidal to toroidal in time. This polarisation rotation is
driven by the magnetic field gradients which develop as the wave fields
phase mix in time. Asymptotically, in an ideal plasma, all the wave
energy is deposited in the toroidal polarisation. We define the time
taken for the toroidal and poloidal amplitudes to become equal as the
ideal poloidal lifetime, tau = lambda(domega_A/dx)^-1 and verify the
result numerically (where lambda is the azimuthal wavenumber, and x
represents the radial direction). Further, by using the method of
multiple timescales, we analytically determine the time dependent wave
solutions and find excellent agreement with our numerical work. The
finite lifetime of ideal poloidal Alfvén waves is important if
the spatial and temporal features of both in-situ satellite and
ground-based observations are to be fully understood.

AB - Standing poloidal Alfvén waves are believed to be excited by
drift-bounce resonance with energetic particle populations in the
Earth's magnetosphere. Using a fully compressible ideal MHD model, in a
cartesian geometry, we investigate the temporal evolution of localised
poloidal Alfvén waves evolving in radially inhomogeneous
magnetoplasmas. We find that the polarisation of these waves rotates
from being poloidal to toroidal in time. This polarisation rotation is
driven by the magnetic field gradients which develop as the wave fields
phase mix in time. Asymptotically, in an ideal plasma, all the wave
energy is deposited in the toroidal polarisation. We define the time
taken for the toroidal and poloidal amplitudes to become equal as the
ideal poloidal lifetime, tau = lambda(domega_A/dx)^-1 and verify the
result numerically (where lambda is the azimuthal wavenumber, and x
represents the radial direction). Further, by using the method of
multiple timescales, we analytically determine the time dependent wave
solutions and find excellent agreement with our numerical work. The
finite lifetime of ideal poloidal Alfvén waves is important if
the spatial and temporal features of both in-situ satellite and
ground-based observations are to be fully understood.

U2 - 10.1016/S0273-1177(97)00716-3

DO - 10.1016/S0273-1177(97)00716-3

M3 - Article

SN - 0273-1177

VL - 20

SP - 489

EP - 492

JO - Advances in Space Research

JF - Advances in Space Research

IS - 3

ER -