A large northern extension of the southern polar coronal hole reached an Earth facing position on the 17th of March 2021. The high solar wind speed stream associated with this coronal hole is anticipated to arrive late on the 19th March and is expected to cause enhanced geomagnetic activity (see Categories of Geomagnetic Activity for more details about these storm levels).
On the previous solar rotation, this coronal hole caused activity to peak at STORM G1 on the 21st February. Geomagnetic storms are statistically more likely around the equinoxes, including March, with negative coronal holes becoming more geo-effective during the spring. Hence, the arrival of this high speed stream is expected to cause activity to reach storm levels to a possible maximum of STORM G2 late on the 19th or early 20th, due to the effects of a Co-rotating Interactive Region (CIR), and as we are close to the spring equinox. As the coronal hole is large in size, the high speed stream is likely to remain geo-effective for a couple of days, with further chances of STORM G1 periods possible.
The timing of coronal hole high-speed solar wind arrival can be often uncertain, but assuming clear, dark skies, there is a greater chance of seeing the aurora late on the evening of the 19th and into the 20th March. Those in Scotland, northern England and Northern Ireland have the better chance if the weather is favourable.
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