Observations of a Comet Tail Disruption Induced by the Passage of a CME

The Solar Mass Ejection Imager observed an extremely faint interplanetary coronal mass ejection (ICME) as it passed Comet C/2001 Q4 (NEAT) on 5 May 2004, apparently causing a disruption of its plasma tail. This is the first time that an ICME has been directly observed interacting with a comet. SMEI's nearly all-sky coverage and image cadence afforded unprecedented coverage of this rarely observed event. The onset first appeared as a kink moving antisunward that eventually developed knots within the disturbed tail. These knots appeared to be swept up in the solar wind flow. We present the SMEI observations as well as identify a likely SOHO/LASCO progenitor of the CME. SMEI observed two other comets (C/2002 T7 [LINEAR] and C/2004 F4 [Bradfield] and at least five similar events during a 35-d period encompassing this observation. Although these had similar morphologies to the 5 May NEAT event, SMEI did not observe any ICMEs in these cases. Three of these were observed close to the heliospheric current sheet indicating that a magnetic boundary crossing may have contributed to the disruptions. However, there are no discernable causes in the SMEI observations for the remaining two events. ; Published in the Journal of Geophysical Research v113 A04101 p1-11, 2008.