For a period of at least a century, scientists say, solar activity has been odd, with the Sun producing only half as many sunspots as expected, and its magnetic poles strangely out of sync.
The Sun creates enormous magnetic fields during its rotation. Often larger than the diameter of the Earth, sunspots are fields of intense magnetic force that create tumultuous solar storms. These storms can cause satellites to short-circuit, disrupt cell phone signals, or damage electrical systems by suddenly piling the charged particles they carry on Earth millions of kilometers away.
Based on historical records, astronomers expected the Sun's 11-year average activity cycle to reach its eruptive peak, known as the solar maximum, this autumn. But Jonathan Cirtain, who works at NASA as a project scientist on the Japanese satellite Hinode, which maps solar magnetic fields, said this summit was just "empty talk."
"I would say activity on the Sun is at its weakest in 200 years," said David Hathaway, head of the solar physics group at NASA's Marshall Space Flight Center in Huntsville, Alabama.
Researchers are baffled. They cannot predict whether this complacency will be temporary or the beginning of a decline that will last for years. This can also mitigate global warming by lowering the Sun's brightness or the wavelength of its rays.
"There is not a single living scientist who has seen such a weak solar cycle," said Andrés Munoz-Jaramillo, who studies the solar magnetic cycle at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.
Complicating the riddle even more is that the Sun is also undergoing one of the strangest magnetic reversals in history.
Normally, the Sun's magnetic north and south change poles approximately every 11 years. During a magnetic field change, the Sun's polar magnetic field weakens to zero and then reappears with the opposite polarity. According to Douglas Biesecker of NASA's Center for Space Environmental Conditions, what scientists know is that it only marks the apex of the solar maximum that makes the magnetic shift noticeable.
But scientists say the Sun's magnetic poles are out of sync in the current cycle. The Sun's north magnetic pole reversed its polarity over a year ago, so it now has the same polarity as the south pole.
“The time it took for the two poles to change was unusually long this time,” says solar physicist Karel Schrijver of the Lockheed Martin Center for Advanced Technology in Palo Alto California.
Scientists say they were surprised by this delay. The Sun's south pole is expected to change its polarity next month, according to satellite measurements of its shifting magnetic poles.
Scientists, on the other hand, cannot explain why sunspots are so rare. Solar physicist Schrijver of the Lockheed Martin Center for Advanced Technology said that sunspots are not only less frequent, but also less active.
📩 13/11/2013 17:08