The occurrence and speed of CMEs related to two characteristic evolution patterns of helicity injection in their solar source regions

Long-term (a few days) variation of magnetic helicity injection was calculated for 28 solar active regions that produced 47 coronal mass ejections (CMEs) to find its relationship to the CME occurrence and speed using SOHO/MDI line-of-sight magnetograms. As a result, we found that the 47 CMEs can be categorized into two different groups by two characteristic evolution patterns of helicity injection in their source active regions, which appeared for 0.5-4.5days before their occurrence: (1) a monotonically increasing pattern with one sign of helicity (GroupA; 30 CMEs in 23 active regions) and (2) a pattern of significant helicity injection followed by its sign reversal (GroupB; 17 CMEs in 5 active regions). We also found that CME speed has a correlation with average helicity injection rate with linear correlation coefficients of 0.85 and 0.63 for GroupA and GroupB, respectively. In addition, these two CME groups show different characteristics as follows: (1) the average CME speed of GroupB (1330kms^-1) is much faster than that of GroupA (870kms^-1), (2) the CMEs in GroupA tend to be single events whereas those in GroupB mainly consist of successive events, and (3) flares related to the CMEs in GroupB are relatively more energetic and impulsive than those in GroupA. Our findings therefore suggest that the two CME groups have different pre-CME conditions in their source active regions and different CME characteristics.