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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 26, issue 6
Ann. Geophys., 26, 1665–1670, 2008
https://doi.org/10.5194/angeo-26-1665-2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 26, 1665–1670, 2008
https://doi.org/10.5194/angeo-26-1665-2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.

  11 Jun 2008

11 Jun 2008

Frequencies of wave packets of whistler-mode chorus inside its source region: a case study

O. Santolik1,2, E. Macusova1,2, E. E. Titova3, B. V. Kozelov3,4, D. A. Gurnett1, J. S. Pickett1, V. Y. Trakhtengerts5,†, and A. G. Demekhov5 O. Santolik et al.
  • 1University of Iowa, Iowa City, Iowa, USA
  • 2permanently at Institute of Atmospheric Physics CAS, Prague and Charles University, Faculty of Mathematics and Physics, Prague, Czech Republic
  • 3Polar Geophysical Institute, Apatity, Russia
  • 4Department of Physics and Technology, University of Tromsø, Tromsø, Norway
  • 5Institute of Applied Physics, Nizhny Novgorod, Russia
  • deceased

Abstract. Whistler-mode chorus is a structured wave emission observed in the Earth's magnetosphere in a frequency range from a few hundreds of Hz to several kHz. We investigate wave packets of chorus using high-resolution measurements recorded by the WBD instrument on board the four Cluster spacecraft. A night-side chorus event observed during geomagnetically disturbed conditions is analyzed. We identify lower and upper frequencies for a large number of individual chorus wave packets inside the chorus source region. We investigate how these observations are related to the central position of the chorus source which has been previously estimated from the Poynting flux measurements. We observe typical frequency bandwidths of chorus of approximately 10% of the local electron cyclotron frequency. Observed time scales are around 0.1 s for the individual wave packets. Our results indicate a lower occurrence probability for lower frequencies in the vicinity of the central position of the source compared to measurements recorded closer to the outer boundaries of the source. This is in agreement with recent research based on the backward wave oscillator theory.

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