Narrow Coronal Mass Ejections

Narrow coronal mass ejections (CMEs), defined arbitrarily as events whose apparent angular width is 15° or less, are a small subset of all CMEs. Little is known of the properties of these events and whether these properties differ from those of the larger, more typical CMEs. We have included in this study 15 narrow CMEs observed in the period from 1999 March through December, and we have examined their structure, angular size, projected radial velocity (speed), and likely surface associations. We find it useful to break these events into two classes: structured and unstructured. Unstructured narrow events are generally narrower and slower than the structured events, but both classes of narrow CMEs exhibit speeds similar to those of larger CMEs. We found that 11 of 15 events studied may be traced to regions on the solar surface near a relatively sharp bend in a polarity-reversal line, as revealed from Hα synoptic maps. We contrast the properties of the narrow CMEs with those of the larger CME population.