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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 22, issue 7
Ann. Geophys., 22, 2555–2563, 2004
© Author(s) 2004. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Spatio-temporal analysis and multipoint measurements in space...

Ann. Geophys., 22, 2555–2563, 2004
© Author(s) 2004. This work is distributed under
the Creative Commons Attribution 3.0 License.

  14 Jul 2004

14 Jul 2004

Multipoint investigation of the source region of storm-time chorus

O. Santolík1,2, D. A. Gurnett1, and J. S. Pickett1 O. Santolík et al.
  • 1Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242-1479, USA
  • 2Now at Faculty of Mathematics and Physics, Charles University, Prague, and at Institute of Atmospheric Physics, Czech Academy of Sciences, Prague, Czech Republic

Abstract. In this case study we investigate the source region of whistler-mode chorus located close to the geomagnetic equator at a radial distance of 4.4 Earth radii. We use measurements from the four Cluster spacecraft at separations of less than a few hundreds of km, recorded during the geomagnetic storm of 18 April 2002. The waveforms of the electric field fluctuations were obtained by the WBD instruments in the frequency range 50Hz-9.5kHz. Using these data, we calculate linear and rank correlation coefficients of the frequency averaged power-spectral density measured by the different spacecraft. Those coefficients have been recently shown to decrease with spacecraft separation distance perpendicular to the static magnetic field cchor03 with a characteristic scale length of 100km. We find this characteristic scale varying between 60 and 200km for different data intervals inside the source region. We examine possible explanations for the observed large scatter of the correlation coefficients, and we suggest a simultaneously acting effect of random positions of locations at which the individual chorus wave packets are generated. The statistical properties of the observations are approximately reproduced by a simple 2-D model of the source region, assuming a perpendicular half-width of 35km (approximately one wavelength of the whistler-mode waves) for the distribution of power radiated from individual active areas.

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