Sunday, July 3

The Sun Is Waking Up — Right On Schedule – Sky & Telescope

solar flare
NASA / GSFC / SDO

The Sun is waking up.

In recent weeks, NASA has announced X-class solar flares, observers have seen large sunspot groups with the unaided eye, and online services have issued multiple aurora alerts even for mid-latitudes.  

After years of quiescence — the Sun was more often spotless than not in 2018, 2019, and 2020 — the change of pace is exciting solar observers. The Sun goes through 11-year cycles of magnetically instigated activity, which include sunspots, flares, and massive eruptions. While such activity last peaked around 2012 through 2014, that maximum was meager at best. In fact, it marked one of the quietest cycles in 100 years.

Now, the uptick in activity seems to mark a change in the Sun’s behavior. Lisa Upton (Space Systems Research Corporation), co-chair of the Solar Cycle 25 Prediction Panel, says that for the first time in 50 years, this solar cycle seems to be stronger than the one before it. She and colleague David Hathaway are predicting that this cycle will be up to 30% more active.

Solar Cycle 25 new predictions
Using the first two years of solar cycle 25 to improve predictions of the rest of the current cycle, Lisa Upton and David Hathaway predict a 20–30% higher sunspot number than in solar cycle 24 — a number still consistent with the forecast of the Solar Cycle 25 Prediction Panel.
L. Upton & D. Hathaway / Yohkoh SXT

“This may mean that we have reached the inflection point in the current Gleissberg cycle and might start to see bigger cycles,” Upton speculates. “It’s a bit too early to say for sure, though.”

However, she emphasizes that we shouldn’t expect too much from the Sun’s current activity. “The cycle is following very nicely along the strongest/earliest of [the panel’s] predictions and is certainly on track to be another weak cycle,” she adds.

“We still consider this cycle to be below average,” confirms panel co-chair Doug Biesecker (National Oceanic and Atmospheric Administration). “Even with the recent activity, the sunspot number is still within the error bars of the solar cycle prediction from the panel.”

Prediction vs. Reality

In 2019, that panel of experts reviewed the available models and predictions for the next solar cycle. In doing so, they recognized that physics-based scenarios were more successful than other prediction methods, such as those based on empirical data of the Sun’s behavior. In particular, the most successful models incorporated the behavior of the Sun’s magnetic fields, especially those at the poles, as well as an understanding energy flow within the turbulent solar interior.  

As a result of these investigations, the panel came to a consensus: That the new solar cycle had started sometime between July 2019 and July 2020, and that activity would peak in 2025 with a maximum sunspot number between 105 and 125. The wiggle room in the prediction reflects that even the physics-based models are not in 100% agreement with one another.

Solar Cycle 25 Prediction Panel forecast
The consensus model from Solar Cycle 25 Prediction Panel (red line) slightly underpredicts the Sun’s current activity (sunspot numbers shown in black). But there’s wiggle room in that prediction: give or take six months for the cycle’s start and give or take 10 sunspots for the daily sunspot number. With an slightly earlier start and higher activity, the panel’s forecast is still spot on.
Space Weather Prediction Center

Now, with two years of the cycle under our collective belt, the predictions are holding up well, albeit with numbers veering toward the earlier and higher end of the forecast. Understanding this slight shift will likely take a year or two more data, but Upton and Hathaway have a report coming out soon with preliminary findings (though you can read a summary of their findings here).   

“I would say that the panel’s forecast for solar cycle 25 is holding up very well,” Upton adds. “I believe this will likely be the best forecast to come out of one of the NOAA/NASA Cycle prediction panels.”

While scientists have a growing confidence in their ability to predict what the Sun will do next, that doesn’t mean there isn’t room for disagreement. Scott McIntosh (National Center for Atmospheric Research), for one, has gone against the consensus in predicting that this cycle will be one of the strongest on record.

By 2023 if not before, it should become clear which prediction is correct.

The Solar Cycle and the 2024 Eclipse

The cycle’s earlier and more active start has some practical consequences. While the original prediction was that the cycle would peak in July 2025, if it started six months early then a six months’ earlier maximum is likely, too. And that would put the maximum closer to the total solar eclipse set to sweep over Central and North America on April 8, 2024.

As the Moon blocks the Sun’s light, it will reveal the corona, the wispy, white solar atmosphere that streams into space — and the corona takes on drastically different shapes depending on solar activity.

“We should have a very interesting Sun to see during the 2024 Great American Eclipse,” Upton says, “certainly very different from the 2017 Great American Eclipse.”


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source: skyandtelescope.org