  Propagation of coronal mass ejections (CMEs) from the Sun far into
interplanetary space is not well understood due to limited observations. In
this study we examine the propagation characteristics of two geo-effective
CMEs, which occurred on 2005 May 6 and 13, respectively. Significant
heliospheric consequences associated with the two CMEs are observed, including
interplanetary CMEs (ICMEs) at the Earth and Ulysses, interplanetary shocks, a
long-duration type II radio burst, and intense geomagnetic storms. We use
coronagraph observations from SOHO/LASCO, frequency drift of the long-duration
type II burst, in situ measurements at the Earth and Ulysses, and
magnetohydrodynamic (MHD) propagation of the observed solar wind disturbances
at 1 AU to track the CMEs from the Sun far into interplanetary space. We find
that both of the two CMEs underwent a major deceleration within 1 AU and
thereafter a gradual deceleration when they propagated from the Earth to deep
interplanetary space due to interactions with the ambient solar wind. The
results also reveal that the two CMEs interacted with each other in the distant
interplanetary space even though their launch times on the Sun were well
separated. The intense geomagnetic storm for each case was caused by the
southward magnetic fields ahead of the CME, stressing the critical role of the
sheath region in geomagnetic storm generation, although for the first case
there is a corotating interaction region involved.
