CMEs are associated with large or magnetically-complex sunspots. Simple sunspots are bipolar, they have a N and a S region with field lines arching up connecti

CMEs are associated with large or magnetically-complex sunspots. Simple sunspots are bipolar, they have a N and a S region with field lines arching up connecting one to the other. Complex sunspots are multipolar, and the field lines therefore cross in weird ways (in the 3D solar plasma). They can change configurations suddenly, releasing a lot of energy as the magnetic field lines re-arrange to a lower-energy configuration. This magnetic reconnection is what drives CMEs (roughly speaking).