Statistical Study of ICMEs with Low Carbon Charge State Plasmas Detected from 1998 to 2011

This work presents a statistical study of 219 ICMEs measured by both the ACE and WIND satellites from 1998 to 2011. ICME plasmas are defined as possessing cold materials if the carbon charge states are lower than those of the preceding solar wind by three standard deviations and the ionic temperature is lower than 10^6.05 K. A total of 69 ICMEs were identified as containing cold materials. These ICMEs tend to have speeds of approximately 400 to 500 kms^-1. And these cold materials tends to occur once or twice per ICME, with durations between 2 and 6 hours. We further identify two special types of cold materials: the ionic-cold type (IC) shows simultaneous lower mean charge states of O, Mg, Si, and Fe ions than those of the preceding solar wind, while the carbon-only cold type(COC) shows a totally opposite trend in that these ions show higher charge state than in the preceding solar wind. We found that the IC type materials have a higher proton temperature than the ICME mean value, whereas the COC type materials have a lower proton temperature than the ICME mean value. One-fourth of the cold materials are found to be related to the bright core of coronal mass ejections (CMEs). The carbon-cold only type materials imply that the filament may be a combination of coronal and chromospheric materials, or it is heated after the carbon ions freeze-in, between 1.2 solar radii and 5 solar radii, during the CME initiation. While, it is difficult to explain the proton heating process in the ionic cold type filament in CMEs.