ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-20-879-2002 Modelling interplanetary CMEs using magnetohydrodynamic simulations Cargill P. J. 2 1 Schmidt J. M. Space and Atmospheric Physics The Blackett Laboratory Imperial College London SW7 2BW, UK Correspondence to: P. J. Cargill (p.cargill@ic.ac.uk) 31 07 2002 20 7 879 890 Copyright: © 2002 P. J. Cargill 2002 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://angeo.copernicus.org/articles/20/879/2002/angeo-20-879-2002.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/20/879/2002/angeo-20-879-2002.pdf

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.<br><br><b>Key words.</b> Interplanetary physics (interplanetary magnetic fields) Solar physics, astrophysics, and astronomy (flares and mass ejections) Space plasma physics (numerical simulation studies)