Production of small-scale Alfvén waves by ionospheric depletion, nonlinear magnetosphere-ionosphere coupling and phase mixing

A. J.B. Russell*, A. N. Wright, A. V. Streltsov

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

20 Citations (Scopus)


Rockets and satellites have previously observed small-scale Alfven waves inside large-scale downward field-aligned currents, and numerical simulations have associated their formation with self-consistent magnetosphere-ionosphere coupling. The origin of these waves was previously attributed to ionospheric feedback instability; however, we show that they arise in numerical experiments in which the instability is excluded. A new interpretation is proposed in which strong ionospheric depletion and associated current broadening (a nonlinear steepening/wave-breaking process) form magnetosphereionosphere waves inside a downward current region and these oscillations drive upgoing inertial Alfven waves in the overlying plasma. The resulting waves are governed by characteristic periods, which are a good match to previously observed periods for reasonable assumed conditions. Meanwhile, wavelengths perpendicular to the magnetic field initially map to an ionospheric scale comparable to the electron inertial length for the low-altitude magnetosphere, but become shorter with time due to frequency-based phase mixing of boundary waves (a new manifestation of phase mixing). Under suitable conditions, these could act as seeds for the ionospheric feedback instability.

Original languageEnglish
Pages (from-to)1450-1460
Number of pages11
JournalJournal of Geophysical Research: Space Physics
Issue number4
Publication statusPublished - 3 Apr 2013


  • Magnetosphere-ionosphere coupling
  • Small-scale Alfven waves
  • Ionospheric depletion
  • Phase mixing
  • Magnetosphere-ionosphere waves
  • Ionospheric feedback instability
  • Quiet auroral arcs
  • Field-line resonances
  • Dynamic magnetosphere
  • Electric fields
  • Model
  • Acceleration
  • Cavity


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