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Astron. Astrophys. 351, 385-392 (1999)


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Spectral analysis of the magnetic field inside particle propagation channels detected by Ulysses

A. Buttighoffer 1,2, L.J. Lanzerotti 2, D.J. Thomson 2, C.G. Maclennan 2 and R.J. Forsyth 4

1 Space Sciences Lab., University of California, Berkeley, CA 94720, USA
2 Lucent Technologies, Bell Laboratories, Murray Hill, NJ 07974, USA
3 Space and Atmospheric Physics, The Blackett Laboratory, Imperial College, London SW7 2BZ, UK

Received 19 August 1998 / Accepted 27 August 1999

Abstract

Prior studies have identified particle propagation channels in the interplanetary medium where nearly scatter-free propagation occurs. These channels have been identified to exist as far away from the Sun as [FORMULA]4 AU. We report here a study that has examined, using spacecraft-based instrumentation, the nature of the fluctuations of the interplanetary magnetic fields inside two such propagation channels as well as in the regions outside the channels. We show that the power spectral fluctuations of the total magnitude of the magnetic field in the entire channel duration encountered are the order of a factor of 10 lower inside the channels than outside. Somewhat surprisingly, in the 1-40 mHz frequency range, we find little change in the slope of the power law spectra from outside to inside the channels. These results provide evidence that the dominant control on the particle pitch angle diffusion coefficients in the channels is the level of power available for particle scattering, and not changes in the shape of the spectra themselves. We have examined the power spectra of each component of the magnetic field and determined that the loss of spectral power is due to a reduction of compressible fluctuations, the solenoidal components of the spectra remaining similar inside and outside the channels.

Key words: Sun: corona – Sun: particle emission – Sun: radio radiation – inteplanetary medium

Present address: LPSH UMR 8645, Observatoire de Meudon, 5 place Janssen, 92195 Meudon, France

Send offprint requests to: A. Buttighoffer (Anne.buttighofer@OBSPM.fr)

© European Southern Observatory (ESO) 1999

Online publication: November 2, 1999

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