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Volume 18, issue 4
Ann. Geophys., 18, 406–410, 2000
© European Geosciences Union 2000
Ann. Geophys., 18, 406–410, 2000
© European Geosciences Union 2000

  30 Apr 2000

30 Apr 2000

Magnetospheric lion roars

W. Baumjohann1, E. Georgescu2,1, K.-H. Fornacon3, H. U. Auster3, R. A. Treumann1, and G. Haerendel1 W. Baumjohann et al.
  • 1Max-Planck-Institut für extraterrestrische Physik, Garching, Germany
  • 2Institut for Space Sciences, Bucharest, Romania
  • 3Institut für Geophysik und Meteorologie, TU Braunschweig, Germany
  • Correspondence to: W. Baumjohann

Abstract. The Equator-S magnetometer is very sensitive and has a sampling rate normally of 128 Hz. The high sampling rate for the first time allows detection of ELF waves between the ion cyclotron and the lower hybrid frequencies in the equatorial dawnside magnetosphere. The characteristics of these waves are virtually identical to the lion roars typically seen at the bottom of the magnetic troughs of magnetosheath mirror waves. The magnetospheric lion roars are near-monochromatic packets of electron whistler waves lasting for a few wave cycles only, typically 0.2 s. They are right-hand circularly polarized waves with typical amplitudes of 0.5 nT at around one tenth of the electron gyrofrequency. The cone angle between wave vector and ambient field is nearly always smaller than 1°.

Key words: Magnetospheric physics (magnetospheric configuration and dynamics; MHD waves and instabilities; plasma waves and instabilities)

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