SciAm: Sun's Recent Behavior Odd: Explanation Elusive

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SciAm: Sun's Recent Behavior Odd: Explanation Elusive

Post by bystander » Thu May 27, 2010 4:47 pm

Solar Scientists Agree That the Sun's Recent Behavior is Odd, but the Explanation Remains Elusive
Scientific American - 27 May 2010
The most recent solar minimum was both long and pronounced. But why?

In very rough terms, the sun's activity ebbs and flows in an 11-year cycle, with flares, coronal mass ejections and other energetic phenomena peaking at what is called solar maximum and bottoming out at solar minimum. Sunspots, markers of magnetic activity on the sun's surface, provide a visual proxy to mark the cycle's evolution, appearing in droves at maximum and all but disappearing at minimum. But the behavior of our host star is not as predictable as all that—the most recent solar minimum was surprisingly deep and long, finally bottoming out around late 2008 or so.

Solar physicists here at the semiannual meeting of the American Astronomical Society this week offered a number of mechanisms to shed light on what has been happening on the sun of late, but conceded that the final answer—or more likely answers—remains opaque. Beyond scientific understanding, motivations for better solar weather forecasts include hopes to use them to safeguard against electrical grid disruptions, damage to Earth-orbiting satellites and threats to the health of space travelers posed by solar radiation flare-ups.

One researcher has looked for clues to solar weather in the meridional flow, which moves from the solar equator toward the poles, and which seems to change speed during the shifting solar cycle. Another looked at the solar "jet stream," a slow current that originates at solar midlatitudes and pushes in a bifurcated stream toward both the equator and the poles. Another scientist examined the inner workings of the sun through the oscillation of sound waves propagating through the solar interior; yet another looked at magnetic maps to chart the shifting flux across the sun.

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Re: SciAm: Sun's Recent Behavior Odd: Explanation Elusive

Post by bystander » Tue Jun 15, 2010 5:26 am

Sun's Strange Behavior Baffles Astronomers
Space.com - 14 June 2010
The sun's temper ebbs and flows on what scientists had thought was a pretty predictable cycle, but lately our closest star has been acting up.

Typically, a few stormy years would knock out a satellite or two and maybe trip a power grid on Earth. Then a few years of quiet, and then back to the bad behavior. But an extremely long stretch of low activity in recent years has scientists baffled and scrambling for better forecasting models.

An expected minimum of solar activity, between 2008 and 2009, was unusually deep. And while the sun would normally ramp up activity by now, heading into its next cycle, the sun may be on the verge of a weak solar cycle instead, astronomers said at the 216th meeting of the American Astronomical Society in Miami last month.

What's wrong with the sun?
New Scientist - 14 June 2010
Sun spots come and go, but recently they have mostly gone. For centuries, astronomers have recorded when these dark blemishes on the solar surface emerge, only for them to fade away again after a few days, weeks or months. Thanks to their efforts, we know that sunspot numbers ebb and flow in cycles lasting about 11 years.

But for the past two years, the sunspots have mostly been missing. Their absence, the most prolonged for nearly a hundred years, has taken even seasoned sun watchers by surprise. "This is solar behaviour we haven't seen in living memory," says David Hathaway, a physicist at NASA's Marshall Space Flight Center in Huntsville, Alabama.

The sun is under scrutiny as never before thanks to an armada of space telescopes. The results they beam back are portraying our nearest star, and its influence on Earth, in a new light. Sunspots and other clues indicate that the sun's magnetic activity is diminishing, and that the sun may even be shrinking. Together the results hint that something profound is happening inside the sun. The big question is what?

The stakes have never been higher. Groups of sunspots forewarn of gigantic solar storms that can unleash a billion times more energy than an atomic bomb. Fears that these giant solar eruptions could create havoc on Earth, and disputes over the sun's role in climate change, are adding urgency to these studies. When NASA and the European Space Agency launched the Solar and Heliospheric Observatory (SOHO) almost 15 years ago, "understanding the solar cycle was not one of its scientific objectives", says Bernhard Fleck, the mission's project scientist. "Now it is one of the key questions."