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Ann. Geophys., 22, 661-671, 2004
www.ann-geophys.net/22/661/2004/
© European Geosciences Union 2004
Predictions of the arrival time of Coronal Mass Ejections at 1AU: an analysis of the causes of errors
M. Owens and P. Cargill
Space and Atmospheric Physics, The Blackett Laboratory, Imperial College, London SW7 2BW, UK
Abstract. Three existing models of Interplanetary Coronal Mass Ejection (ICME) transit between the Sun and
the Earth are compared to coronagraph and in situ observations: all three models are found to
perform with a similar level of accuracy (i.e. an average error between observed and predicted 1AU
transit times of approximately 11h). To improve long-term space weather prediction,
factors influencing CME transit are investigated. Both the removal of the plane of sky projection
(as suffered by coronagraph derived speeds of Earth directed CMEs) and the use of observed values
of solar wind speed, fail to significantly improve transit time prediction. However, a correlation is
found to exist between the late/early arrival of an ICME and the width of the preceding sheath
region, suggesting that the error is a geometrical effect that can only be removed by a more accurate
determination of a CME trajectory and expansion. The correlation between magnetic field intensity
and speed of ejecta at 1AU is also investigated. It is found to be weak in the body of the ICME,
but strong in the sheath, if the upstream solar wind conditions are taken into account.
Key words. Solar physics, astronomy and astrophysics
(flares and mass ejections) – Interplanetary physics (interplanetary
magnetic fields; sources of the solar wind)
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