Multiple-timescales analysis of ideal poloidal Alfvén waves.

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Abstract

Time-dependent analytic solutions for the evolution of undriven ideal standing poloidal Alfven waves are considered in a box model magnetosphere. Assuming an ''aximuthal'' variation of exp i lambda y, where lambda is large, we use the asymptotic method of multiple timescales to determine analytic solutions over the long timescale a defined by sigma = epsilon t, where epsilon 1/lambda. Our asymptotic poloidal Alfven wave solutions (with lambda >> k(x), k(z)) accurately reproduce the undriven ideal wave polarization rotation from poloidal to toroidal in time determined numerically by Mann and Wright [1995]. Using the same asymptotic method, we further consider the evolution of radially localized large lambda Alfven waves. We find that undriven waves having k(x), lambda >> k(z), oscillating in a radially inhomogeneous plasma remain incompressible to leading order and experience similar asymptotically toroidal behavior as t --> infinity. Consequently, undriven poloidal Alfven waves and, in general, transversally localized large lambda ideal Alfven wave disturbances have a finite lifetime before they evolve into purely decoupled toroidal Alfven waves. This polarization rotation may be apparent in waves driven by the drift-bounce resonance mechanism in situations where the wave evolution occurs more rapidly than ionospheric damping. This can be possible on the dayside of the magnetosphere, with the evolution more likely to be observable toward the end of a temporal wave packet when the driving mechanism is no longer operative.

Original languageEnglish
Pages (from-to)2381-2390
Number of pages10
JournalJournal of Geophysical Research
Volume102
Issue numberA2
DOIs
Publication statusPublished - 1 Feb 1997

Keywords

  • FIELD LINE RESONANCE
  • GEOMAGNETIC-PULSATIONS
  • MAGNETIC PULSATION
  • SYNCHRONOUS ORBIT
  • GIANT PULSATION
  • PG-PULSATION
  • MAGNETOSPHERE
  • PLASMA
  • RADAR
  • OSCILLATIONS

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