In a hot gas ions and electrons bounce around with greater speed, and when they collide, more energy is released. Dark areas of the corona, seen in EUV or X-rays. The solar wind coming from coronal holes seems to move faster. Coronal holes probably occur in regions where the magnetic field does not greatly impede the flow of plasma. Weak magnetic fields, on the other hand, get instead pushed around by the plasma, which modifies their structure.
Sunspots are sources of strong magnetism.
Ions and electrons guided along such arches by their strong magnetic fields find it hard to escape. In between sunspot groups, field lines stick out like blades of grass after a rain, and plasma can ride along them outwards. Spacecraft in the solar wind observe there a weak magnetic field. The field comes out from the Sun, and is dragged out by the solar wind. CMEs are big bubbles of plasma, threaded by field lines of the Sun, which get blown away by releases of magnetic energy.