Coronal Holes and Fast Solar Wind

The dark spot across the north pole of the Sun – as captured in this image on July 31, 2020, from NASA’s Solar Dynamics Observatory, or SDO – is an area of relatively cooler material in the solar atmosphere, known as a coronal hole. Coronal holes are regions on the Sun where the magnetic field is open to interplanetary space, sending solar material speeding out in a high-speed stream of solar wind.  (The extreme ultraviolet light in this SDO image is normally invisible to the eye, but is colorized here in bronze.)

In this case, instruments such as those on NOAA’s DSCOVR spacecraft observed a high-speed stream arrival on Aug. 2. and climb in speed over the next couple days, as can be seen in the graph of the solar wind speed shown here.

Coronal holes appear throughout the Sun’s approximately-11-year solar cycle, but can last for much longer periods of time during solar minimum – a period of time when activity on the Sun is substantially diminished, and which the Sun is just beginning to wake up from now.