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Astron. Astrophys. 335, 1101-1110 (1998)

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Particle acceleration efficiency and MHD characteristics of CIR-related shocks

H.-T. Claßen 1, G. Mann 1 and E. Keppler 2

1 Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany
2 Max-Planck-Institut für Aeronomie, Postfach 20, D-37191 Katlenburg-Lindau, Germany

Received 15 July 1997 / Accepted 28 April 1998

Abstract

During its southbound journey the Ulysses spacecraft crossed a series of corotating interaction regions (CIRs) building up due to the interaction of fast and slow solar wind streams. We analyse the forward and the reverse shocks marking off the 18 CIR encounters between July 1992 and December 1993. Our investigations look for a correlation between the particle acceleration efficiency expressed by the particle flux measured at the time of shock crossing and the MHD characteristics of the shocks; i.e., Alfven-Mach number ([FORMULA]), density and magnetic field compression ratios ([FORMULA], [FORMULA]), and the angle between shock normal and upstream magnetic field ([FORMULA]). The results of this analysis show that the highest fluxes of 300 keV electrons and 1 MeV protons are observed when the conditions [FORMULA] and [FORMULA] are simultaneously fulfilled by the shocks. These investigations are supplemented by a computation of the first critical Alfven-Mach number for typical parameters of CIR-related shocks. Furthermore, we discuss possible acceleration mechanisms by an analysis of the spectral indices of protons and Helium.

Key words: solar wind – interplanetary medium – acceleration of particles – shock waves

Send offprint requests to: H.-T. Claßen

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© European Southern Observatory (ESO) 1998

Online publication: June 26, 1998
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