The Solar and Heliospheric Observatory (SOHO) spacecraft may have glimpsed the first sunspot of the next 11-year solar cycle. It has come a tad early, and it may mean that the next sunspot cycle will be a particularly active one.
“It’s kind of like the first swallow of spring,” says David Hathaway, a solar physicist at NASA’s Marshall Space Flight Center in Huntsville, Alabama, US. “It’s the first indication that the next cycle is starting.”
Sunspots are formed when magnetic fields that have been made deep inside the Sun become buoyant, rise up through the Sun and erupt through the surface, causing a dark, relatively cool, spot.
The number of sunspots varies on a period of about 11 years, the same timescale that the Sun’s magnetic poles reverse direction. The next 11-year cycle was predicted to begin by March 2007.
But an unusual sunspot on 30 July may signal an early start of that cycle. For the past several years, sunspots in the Sun’s southern hemisphere have been oriented north-south. This one, however, was magnetically backwards and had a south-north bent.
But the sunspot was short-lived. SOHO, a joint project of the European Space Agency and NASA, first spotted it at 2200 GMT on 30 July, then saw it again at midnight.
By 1000 GMT on 31 July, the spot had disappeared. Of a handful of US Air Force observatories, two must see a sunspot for it to get an official number designation. But the spot lasted long enough for just one of them to glimpse it.
And the sunspot had another unusual feature – it cropped up at a latitude of about 13º. The first sunspots of a new cycle usually show up at latitudes higher than 20º, then slowly migrate towards the equator.
“The fact this one was at that low a latitude was a little bit of a surprise, but it is not out of the ordinary,” Hathaway told New Scientist.
And the “backwards” sunspot is not the only indication that the Sun’s magnetic poles are reversing. SOHO has previously observed looped magnetic fields on the Sun that had started to reverse their polarity, but the fields were not strong enough to create sunspots.
And the sunspot may signal that the next sunspot cycle will be quite active. That is because it occurred relatively early in the predicted window, says Hathaway.
That assessment is in line with predictions by researchers at the National Center for Atmospheric Research in Colorado, who suggest that this upcoming sunspot cycle might produce more sunspots than any other cycle since the 1950s (see Bumper sunspot crop forecast for next solar cycle.)
The Colorado group developed a computer model that predicted past sunspot cycles with 98% accuracy. Based on that model, the team predicts that this cycle should be 30% to 50% stronger than the current solar cycle and rivalled only by the solar maximum of 1958.
And two other indicators – Earth’s geomagnetic activity and the flow of sunspots – also indicate the upcoming cycle has the potential for a lot of solar activity, Hathaway says.
Before the sunspot minimum, there is often a flurry of geomagnetic activity, as measured by high-tech compasses that show small vibrations in the Earth’s magnetic field.
The cause of these vibrations is not clear, but the level of activity detected is a predictor of how active the next sunspot cycle is going to be. Observations before the most recent sunspot minimum suggest the next cycle will be quite dynamic, he says.
The other indicator looks at how fast bands of sunspots move on a “conveyor belt” from low latitudes towards the poles. When that flow is relatively fast, strong magnetic fields are thought to build up at the poles.
From there, the sunspots are thought to sink down into the Sun, emerging about 20 years later back at lower latitudes. “It takes that long for that conveyor belt to carry things from the poles back underneath surface of the Sun back towards the equator,” Hathaway says.
About 20 years ago, the sunspots appeared to be moving quickly towards the poles, suggesting their strong magnetic fields will emerge even stronger after being stretched on their way through the Sun.
But another group, led by Leif Svalgaard of ETK, a consulting firm in Houston, Texas, US, contends that the upcoming solar cycle will not be very strong because the magnetic fields at the poles are currently weak. That group is calling for the weakest solar cycle in 100 years. Kelly Young, New Scientist