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Ann. Geophys., 20, 879-890, 2002
www.ann-geophys.net/20/879/2002/
© European Geosciences Union 2002
Modelling interplanetary CMEs using magnetohydrodynamic simulations
P. J. Cargill and J. M. Schmidt
Space and Atmospheric Physics The Blackett Laboratory Imperial College London SW7 2BW, UK
Correspondence to: P. J. Cargill (p.cargill@ic.ac.uk)
Abstract. The dynamics of
Interplanetary Coronal Mass Ejections (ICMEs) are discussed from the viewpoint
of numerical modelling. Hydrodynamic models are shown to give a good zero-order
picture of the plasma properties of ICMEs, but they cannot model the important
magnetic field effects. Results from MHD simulations are shown for a number of
cases of interest. It is demonstrated that the strong interaction of the ICME
with the solar wind leads to the ICME and solar wind velocities being close to
each other at 1 AU, despite their having very different speeds near the Sun. It
is also pointed out that this interaction leads to a distortion of the ICME
geometry, making cylindrical symmetry a dubious assumption for the CME field at
1 AU. In the presence of a significant solar wind magnetic field, the magnetic
fields of the ICME and solar wind can reconnect with each other, leading to an
ICME that has solar wind-like field lines. This effect is especially important
when an ICME with the right sense of rotation propagates down the heliospheric
current sheet. It is also noted that a lack of knowledge of the coronal
magnetic field makes such simulations of little use in space weather forecasts
that require knowledge of the ICME magnetic field strength.
Key words. Interplanetary physics (interplanetary
magnetic fields) Solar physics, astrophysics, and astronomy (flares and mass
ejections) Space plasma physics (numerical simulation studies)
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