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Ann. Geophys., 22, 2245-2254, 2004
www.ann-geophys.net/22/2245/2004/
© European Geosciences Union 2004
A numerical study of two interacting coronal mass ejections
J. M. Schmidt and P. J. Cargill
Space and Atmospheric Physics, The Blackett Laboratory, Imperial College, London, UK
Abstract. The interaction in the solar wind between two coronal mass
ejections (CMEs) is investigated using numerical simulations. We show that
the nature of the interaction depends on whether the CME magnetic structures
interact, but in all cases the result is an equilisation of the speed of the
two CMEs. In the absence of magnetic interaction, the forward shock of the
faster trailing CME interacts with the slow leading CME, and accelerates it.
When the two CMEs have magnetic fields with the same sense of rotation,
magnetic reconnection occurs between the two CMEs, leading to the formation
of a single magnetic structure: in the most extreme cases, one CME "eats"
the other. When the senses of rotation are opposite, reconnection does not
occur, but the CMEs collide in a highly non-elastic manner, again forming a
single structure. The possibility of enhanced particle acceleration in such
processes is assessed. The presence of strong magnetic reconnection provides
excellent opportunities for the acceleration of thermal particles, which
then form a seed population for further acceleration at the CME shocks. The
presence of a large population of seed particles will thus lead to an
overall increase in energetic particle fluxes, as suggested by some
observations.
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