The Space Weather News for May 23, 2021 reads (with some highlighting by me)

Yesterday, the sun produced a sequence of solar flares unlike anything we've seen in years movie. Earth-orbiting satellites detected a dozen explosions in the magnetic canopy of sunspot AR2824. One of them emitted a radio burst so strong, it drowned out static from lightning storms on Earth and was recorded at midnight by listening stations in the Arctic. NOAA forecast models suggest that a CME might hit Earth's magnetic field on May 26th.

As non-expert of that field, I have a couple of comprehension questions:

  1. What is a "magnetic canopy of a sunspot"? Is there a definition for that, or does it just mean "magnetic flux tube coming originating at the sunspot"?
  2. Why is that solar flare so spectacular? Which parameters are the most extreme ones? Where could I find more on the statistics of those parameters? What exactly does "in years" mean here? How rare are which parameters of the May-23-flare?
  3. How are sunspots named? A quick search showed that AR2824 seems to be around for quite a while, but I did find anything about whether that is a simple counter, or there are different prefixes, other than AR.
  4. It is said that the "CME might hit Earth's magnetic field", which is probably not same as "it will hit Earth", or is it? Could somebody please guide me how this is read from the (above linked) NOAA forecast model graphs? Do these models give a probablity of a CME reaching Earth? How likely is it that this CME might disturb any satellite?

In short: I would appreciate a quantified and expanded version of the quoted news, enriched with some definitions for the non-experts.

References and related questions

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    $\begingroup$ That's a lot of questions for a single post... Number #3 and #4 would deserve their own, separate questions IMHO. $\endgroup$ Commented May 24, 2021 at 10:09
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    $\begingroup$ The author of Space Weather News is a space weather enthusiast. The last few years have been rather boring from a space weather perspective. The entirety of solar cycle 24 was rather boring from a space weather perspective. Now we're on the brink of solar cycle 25. Maybe that won't be so boring. (Some think it will be even more boring than solar cycle 24.) Think of him as the equivalent of tornado hunters who get excited at the report of the first F1 tornado of the year, and even more excited about the first F2. That's all this event was, the equivalent of the first F2 tornado of the year. $\endgroup$ Commented May 24, 2021 at 10:37
  • $\begingroup$ Now, that there are already 3 answers, it seems unwise to separate my questions, but I maybe ask a related one focusing on the "sunspot names". This question was mainly targeting the issue that the press release confused me. $\endgroup$
    – B--rian
    Commented May 25, 2021 at 7:33
  • $\begingroup$ @Jean-MariePrival I just asked Are sunspots named or individually tracked $\endgroup$
    – B--rian
    Commented May 25, 2021 at 15:56

3 Answers 3


How are the solar flares from May 23, 2021 extraordinary?

They weren't at all extraordinary. The Sun has been quiescent for the last three or so years. This quiescence is typical of the period between solar cycles. Solar cycle 25 is finally becoming a tiny bit active.

What is a "magnetic canopy of a sunspot"?

Bad prose. An active region on the Sun is an area with an especially strong magnetic field.. Normally the magnetic field lines surrounding an active region are closed; they loop back toward the Sun. I guess one could call this looping the "magnetic canopy of a sunspot." Occasionally the loops break. That break of the loop results in a solar flare or a coronal mass ejection.

Why is that solar flare so spectacular?

It wasn't. That active region resulted in 9 C class flares and 2 M class flares. That's nothing compared to what we will see in a few years, and those in turn most likely will be nothing compared to the Carrington Event. The Sun is coming out of its solar minimum slumber.

How are sunspots named?

Sunspots are neither named nor numbered. Active regions on the Sun however are numbered, and have been since 05 January 1972. Active regions can have several sunspots, or none. The numbering of active regions is consecutive. The standard practice is to report only the last four digits and the date.

It is said that the "CME might hit Earth's magnetic field", which is probably not same as "it will hit Earth", or is it?

CMEs typically hit the Earth's magnetic field rather than the Earth. Only the very strongest CME's can punch through the Earth's magnetic field. People living at high latitudes might see some nice auroras (aurora borealis (northern lights), and aurora australis (southern lights) from this event.

When a CME hits the Earth's magnetic field, the field channels most of the particles around and away from the hitting the Earth. Some of the particles end up getting channeled toward the Earth's poles. This channeling of some of the particles toward the Earth's magnetic poles is why those auroras occur. Even something as strong as a Carrington-level event will have the greatest impact at high latitudes.

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    $\begingroup$ Currently, the planetary $\text K_{\text p}$ index is predicted to peak at 6 on May 26, 2021. This means people living as far south as the northern US might get a barely visible nighttime light show. This moderate level of activity happens about 600 times per solar cycle. (A solar cycle lasts approximately 11 years.) This does not qualify as "extraordinary". $\endgroup$ Commented May 24, 2021 at 11:08
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    $\begingroup$ The nighttime light show most likely will be nice from Alaska, as well as from northern Canada, northern Europe, and northern Russia. But this was not an extraordinary event. $\endgroup$ Commented May 24, 2021 at 11:21

Could somebody please guide me how this is read from the (above linked) NOAA forecast model graphs?

The yellow dot is the sun, the green dot is the position of the Earth. The CME is the blob of high speed / high density plasma that shoots out of the sun at the beginning of the video (the twisted bands that are present on the maps are coronal hole streams). The model shows the edge of the CME hitting us, but the densest part of it looks like it will pass far to the east of us, lessening the impact.

As others have said, this isn't a huge deal — flares and CMEs of this magnitude are an ordinary occurrence and not expected to cause any trouble on Earth. At M1.4, the intensity of the strongest flare from this region was a little under 1% that of the X15 flare associated with the 1989 geomagnetic storm. It's just that we have been in a long and quiet solar minimum, with practically no activity since September of 2017, so this is further proof that we're on the upswing of the solar cycle.

All that said, there was an isolated M4.4 flare in November of 2020, so this one is not the first M-class flare in years, nor the largest one in years — that one was!


According to NOAA's Space Weather Prediction Center there was a Solar radio burst at 245 MHz at ~21:30 UTC that was 3300 flux units above background (1 flux unit $= {\rm 10^{-22} Wm^{-2} Hz^{-1}}$) on 2021-05-22. I'm not sure what they mean by "solar flares unlike anything we've seen in years". There was a radio burst at 610 MHz on 2020-12-07 that was 9200 flux units above background and a burst on 2017-09-10 that was 21000 flux units above background. Historical burst data can be found at ftp://ftp.ngdc.noaa.gov/STP/swpc_products/daily_reports/solar_event_reports/

Maybe the solar activity was more exciting on other bands. Hopefully others will chime in to answer your other questions. I'd be interested in the answers as well.

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    $\begingroup$ I think a significant word in the quote may be "sequence". The individual flares weren't unusual by themselves, but a dozen together was. $\endgroup$
    – Barmar
    Commented May 24, 2021 at 13:50
  • $\begingroup$ @Barmar Very valuable hint, thanks! $\endgroup$
    – B--rian
    Commented May 24, 2021 at 14:32

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