The Relationship between Stealth CMEs and Coronal Holes: Origin, Interaction, and Geoeffectiveness

The current solar cycle is unique in that levels of activity are the lowest for any cycle since the space age in terms of a shortage of strong geomagnetic storms and high-energy particle events (e.g. ground-level events (GLEs)). This low level of activity has brought about unique challenges. One of these is the rise in "stealth CMEs," which are CMEs observed in coronagraph data but not in coronal images, especially in disk view. These events were identified during the deep minimum of cycle 23/24 and appear to be increasing. Since solar cycle 25 brings with it the possibility of yet another low activity cycle, it is very likely that the number of stealth CMEs will remain a significant fraction of ejecta. Thus a better understanding of their eruption mechanisms, the timescale over which on-disk observations must be made for unambiguous identification, and a reliable association with ICME events at 1 AU are of paramount importance to space weather prediction in the coming cycle. It is not yet clear if stealth CMEs represent a new class of CMEs that cannot not be explained in terms of standard models. However, they cannot be ignored. Under certain circumstances these events have been known to drive large geomagnetic storms. We investigate the existence of mismatched polarity reversals in the magnetic field and electron strahl measured in situ within ICMEs associated with stealth CMEs. We discuss the plausibility of interaction with solar wind emanating from coronal holes as a key element of stealth CME eruption as evidenced by expanding coronal hole boundaries during eruption and the presence of interchange reconnection within ICMEs.