On resonance properties of the Earth's magnetosphere

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   The Earth's magnetosphere is formed by the interaction of the solar wind
   with the geomagnetic field and look like almost an empty cavity with very
   rarefied plasma. The boundary of the magnetosphere (magnetopause) is quite
   sharp from the side of oncoming solar wind and becomes blurred with
   distance in the geotail. Such structure of the magnetosphere was the basis
   for consideration the magnetosphere as a giant natural MHD resonator.
   Eigen-oscillations of the resonator appear in the form of various MHD
   oscillations - Alfven waves and fast (FMS) and slow (SMS) magnetosonic
   waves. Alfven and SMS waves propagate almost along the geomagnetic field
   lines. Because the footpoints of all field lines lie on the
   high-conductive ionosphere, which reflects well these MHD oscillations,
   they form a standing waves along the field lines. Alfven waves are the
   only ones of MHD oscillations, where the electric field component in the
   direction along the magnetic field lines is exited. This makes it possible
   to change the pitch angle distribution of the magnetospheric plasma
   particles, which leads to their precipitation into the ionosphere and
   formation of aurora.

   Both the Alfven and SMS waves can be excited in the magnetosphere by their
   interaction with fast magnetic sound on the resonance surfaces. FMS waves
   can penetrate into the magnetosphere from the solar wind, or be excited in
   shear flow at the magnetopause, when solar wind flowing around the
   magnetosphere (Kelvin-Helmholtz instability). Inhomogeneity of the Earth's
   plasma creates cavity resonators for FMS waves in the magnetosphere, which
   eigen-frequencies are allocated in the observations in the lowest
   frequency parts of geomagnetic pulsation spectra. SMS waves, unlike the
   Alfven waves, strongly decay usually during the interaction with the
   background plasma. This enables the transfer of momentum from the solar
   wind into the magnetosphere with the flux of FMS waves and subsequent
   resonant excitation of SMS waves that transmit impulse to background
   magnetospheric plasma. One of the branches of the magnetospheric
   convection can be formed in this way in the geomagnetic tail lobes
   adjacent to the magnetopause.