The solar region with open magnetic field lines that releases high-speed solar wind is a coronal hole. It is not a literal hole in the Sun, but a cooler, less dense area of the corona that appears dark in extreme-ultraviolet and X-ray images.
In most of the corona, magnetic field lines form closed loops that help confine hot plasma. Inside a coronal hole, many field lines remain open and extend outward into interplanetary space. Plasma can escape along these channels, producing the fast solar-wind component, commonly traveling about 600–800 kilometers per second near Earth’s orbit.
Coronal holes are especially prominent near the solar poles during periods of low solar activity, though they can also form at lower latitudes during other phases of the roughly 11-year solar cycle. When a fast stream from a persistent coronal hole catches slower solar wind ahead of it, the interaction can create recurring geomagnetic activity and auroras.