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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 24, issue 7
Ann. Geophys., 24, 1993–2004, 2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 24, 1993–2004, 2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.

  09 Aug 2006

09 Aug 2006

VLF/ELF wave activity in the vicinity of the polar cusp: Cluster observations

N. Lin1, E. S. Lee1, J. McFadden1, G. Parks1, M. Wilber1, M. Maksimovic2, N. Cornilleau-Wehrlin3, A. Fazakarley4, E. Lucek5, H. Rème6, O. Santolik7, and Q.-G. Zong8,* N. Lin et al.
  • 1Space Sciences Laboratory, UC Berkeley, Berkeley, CA 94720, USA
  • 2LESIA, Observatoire de Paris, 92195 Meudon Cedex, France
  • 3CETP/UVSQ, 10-12 Av. De l’Europe, 78140 Velizy, France
  • 4Mullard Space Science Laboratory, Univ. College, London, UK
  • 5Space and Atmospheric Physics, Imperial College, London, SW7 2BZ, UK
  • 6CESR, 9 ave du Colonel Roche, 31028Toulouse Cedex 4, Toulouse, France
  • 7Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
  • 8Center for Space Physics, Boston University, Boston, MA 02215, USA
  • *now at: Center for Atmospheric Research, University of Massachusetts Lowell, Lowell, MA 01854, USA

Abstract. Observations by the Cluster spacecraft of VLF/ELF wave activity show distinct signatures for different regions in the vicinity of high altitude polar cusps, which are identified by using magnetic field and plasma data along spacecraft trajectories. These waves include: (1) Broad band magnetic noise observed in the polar cusp at frequencies from several Hz to ~100 Hz, below the local electron cyclotron frequency, fce. Similar magnetic noise is also observed in the high latitude magnetosheath and the magnetopause boundary layer. (2) Strong broad band electrostatic emissions observed in the cusp, in the magnetosheath, and in the high latitude magnetopause boundary layer, at frequencies extending from several Hz to tens of kHz, with maximum intensities below ~100 Hz. (3) Narrow-band electromagnetic whistler waves at frequencies ~0.2–0.6 fce, frequently observed in the closed boundary layer (CBL) adjacent to the polar cusp. These waves are for the first time observed in this region to be accompanied by counter-streaming electron beams of ~100 eV, which suggests that the waves are excited by these electrons through wave-particle interaction. (4) Narrow-band electrostatic waves observed slightly above the local fce in the CBL. (5) Lion roars, observed in the high latitude magnetosheath, often in magnetic troughs of mirror mode oscillations. The above wave signatures can serve as indicators of the regions in the vicinity of the magnetospheric cusp.

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