Global Coronal Mass Ejections

Observations of the low solar corona in the extreme ultraviolet and in soft X-rays evidence a close relationship of coronal dimmings and coronal mass ejections (CMEs). Dimmings are usually interpreted as places of plasma evacuation during a CME. We characterize a CME by the apparent angular extent of associated dimmings above the solar limb and define a global CME as a CME with the total apparent extent of limb dimmings of more than 180 degree . Several examples of global CMEs are discussed. All the global CMEs identified up to now are fast full-halo CMEs associated with X-class flares (if they originate on the front side of the Sun). We demonstrate that global CMEs involve an eruption of several magnetic flux systems distributed on a large spatial scale comparable to one-half of the solar disk (true angular width around 180 degree ). We discuss possible interpretations of the global CME phenomenon and challenges it presents to CME modeling. Our results suggest a nonlocal nature of the CME eruption mechanism.