B for BOMB: Big sunspot is crackling with B-class solar flares although we are in a long and deep SOLAR MINIMUM

Although an international panel of researchers has predicted that the current solar minimum is going to deepen, potentially reaching a century-class low in the next year or so, big sunspot AR2738 is crackling with B-class solar flares:

astrophotographer Philippe Tosi caught the sunspot in mid-flare, inserting an image of Earth for scale. By P. Tosi via SpaceWeather.com

On the Richter Scale of Solar Flares, B-class events are considered weak. In solar physics, however, such terms are relative. A typical B-class solar flare releases as much energy as 100 million WWII atomic bombs. Only on the sun, which is itself a 1027 ton self-contained nuclear explosion, would such a blast be considered “weak.”

Despite the objective potency of B-flares, they have little effect on Earth. Their UV output causes short-lived waves of ionization to ripple through our planet’s upper atmosphere, subtly affecting the propagation of shortwave radio waves. That’s it.

An M-class or X-class flare would have more impact, but the relatively simple magnetic field of sunspot AR2738 does not appear to harbor sufficient energy for those more powerful explosions.

Weak solar cycle 25

The panel predicts a “fairly weak” Solar Cycle 25. What does that mean? Saying that a solar cycle is “weak” is a bit like saying hurricane season will be “weak.” In other words, there may be fewer storms, but when a storm comes, you’d better batten down the hatches. “Weak” Solar Cycle 24 produced a number of intense X-class solar flares, strong geomagnetic storms, and even a Ground Level Event (GLE) when solar energetic particles reached Earth’s surface. An equally “weak” Solar Cycle 25 could do the same 3 or 4 years hence.


Solar Minimum

Meanwhile, we have solar minimum. This is a widely misunderstood phase of the solar cycle. Many people think it brings a period of dull quiet. In fact, space weather changes in interesting ways. For instance, as the sun’s magnetic field weakens, holes open in the sun’s atmosphere. Emerging streams of solar wind buffet Earth’s magnetic field, sustaining auroras even without solar flares and sunspots. Some observers believe that Solar Minimum auroras have a distinctive palette, pinker than during other phases of the solar cycle.

The sun’s weakening magnetic field also allows cosmic rays to enter the solar system. Energetic particles from deep space penetrate Earth’s atmosphere with a myriad of possible effects ranging from changes in upper atmospheric electricity to extra doses of radiation for people on airplanes.

Finally, the sun dims, especially at extreme ultraviolet wavelengths. This, in turn, causes the upper atmosphere to cool and contract. Aerodynamic drag that would normally cause satellites to decay is reduced; space junk accumulates. This effect makes solar minimum a terrible time to blow up satellites–although people do it anyway.

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[Spaceweather, Spaceweatherarchive]

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