A region on the sun which is active. Active regions contain strong magnetic fields. Flares occur within active regions. The outer atmosphere of the sun with low density and high temperature. Visible as an extended bright region about the sun during a solar eclipse.
Coronal holes are the sources of high-speed solar wind streams.
An ejection of material from the sun into interplanetary space. If the material is directed toward Earth, then the event is associated with a disturbance to the Earth's magnetic field or ionosphere. At times, the whole HF spectrum is affected, but normally the lower frequencies are affected most. Only those circuits with daylight sectors can be affected. An explosion on the sun usually releasing large amounts of energy and particles, and usually occurring within an active region.