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Ann. Geophys., 24, 1993-2004, 2006
www.ann-geophys.net/24/1993/2006/
© European Geosciences Union 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,*
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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