Resonant Cavities and Waveguides in the Ionosphere and Atmosphere

R. L. Lysak, A. Yoshikawa

Research output: Chapter in Book/Report/Conference proceedingChapter

20 Scopus citations


The strong inhomogeneities in plasma parameters in the ionosphere and adjacent regions can trap waves in the upper end of the ULF range (Pc1/Pi1). The topside ionosphere is characterized by a rapidly increasing Alfvén speed with a scale height on the order of 1000 km. Shear-mode Alfvén waves in this region can be partially trapped at frequencies in the 0.1-1.0 Hz range. The same structure can trap fast-mode compressional waves in this frequency band. Since these waves can propagate across magnetic field lines, this structure constitutes a waveguide in which energy can propagate at speeds comparable to the Alfvén speed, typically on the order of 1000 km/s. Hall effects in the ionosphere couple these two wave modes, so that the introduction of a field-aligned current by means of a shearmode Alfvén wave can excite compressional waves that can propagate in the waveguide. In the limit of infinite ionospheric conductivity, these waves are isolated from the atmospheric fields; however, for finite conductivity, ionospheric and atmospheric waves are coupled. Transverse magnetic modes in the atmosphere can propagate at ULF frequencies and form global Schumann resonances with the fundamental at 8 Hz. It has been suggested that signals that propagate at the speed of light through this atmospheric waveguide can rapidly transmit signals from the polar region to lower latitudes during sudden storm commencements.

Original languageEnglish (US)
Title of host publicationMagnetospheric ULF Waves
Subtitle of host publicationSynthesis and New Directions
Number of pages18
ISBN (Electronic)9781118666319
ISBN (Print)0875904343, 9780875904344
StatePublished - Mar 18 2013

Bibliographical note

Publisher Copyright:
© 2006 by the American Geophysical Union.


  • Dynamics of a particle
  • Magnetohydrodynamic instabilities
  • Magnetohydrodynamic waves
  • Magnetosphere
  • Magnetospheric physics


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