Also known as a coronal hole, it just means there’s a large dark area in the atmosphere that is cooler than its surroundings.

Source: https://www.huffingtonpost.co.uk/entry/where-northern-lights-uk-march_uk_6425626ee4b02a8d518cc4a7

Data from RHESSI provided vital clues about solar flares and their associated coronal mass ejections.

Source: https://ummid.com/news/2023/april/18.04.2023/retired-nasa-satellite-to-crash-into-earth-wednesday.html

"There is a recent idea that coronal loops might just be optical illusions," said Terry Kucera, STEREO project scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

Source: https://phys.org/news/2023-08-years-nasa-stereo-a-spacecraft-earth.html

The space weather phenomena has been triggered by a "coronal hole" in the outer layer of the Sun's atmosphere - the second to manifest in the last week.

Source: https://www.express.co.uk/news/science/1752762/northern-lights-northern-scotland-space-weather

This week, multiple coronal mass ejections (CMEs) were emitted by the sun and traveled at high speeds towards Earth, impacting our planet's magnetic field and resulting in auroras.

Source: https://www.dailymail.co.uk/galleries/article-12810421/Huge-solar-storm-strike-Earth-bring-Northern-Lights.html?ns_mchannel=rss&ns_campaign=1490&ito=1490