"The Great Switch" --Sun's Magnetic Field Does a Complete Reverse Every 11 Years
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April 21, 2012

"The Great Switch" --Sun's Magnetic Field Does a Complete Reverse Every 11 Years

 

           Sdo1a


About every 11 years the magnetic field on the sun reverses completely – the north magnetic pole switches to south, and vice versa. This flip coincides with the greatest solar activity seen on the sun in any given cycle, known as "solar maximum."

While the cycle unfolds with seeming regularity every 11 years, in two upcoming papers scientists highlight just how asymmetrical this process actually is. Currently the polarity at the north of the sun appears to have decreased close to zero – that is, it seems to be well into its polar flip from magnetic north to south -- but the polarity at the south is only just beginning to decrease.

"Right now, there's an imbalance between the north and the south poles," says Jonathan Cirtain, a space scientist at NASA's Marshall Space Flight Center in Huntsville, Ala., who is also NASA's project scientist for a Japanese solar mission called Hinode. "The north is already in transition, well ahead of the south pole, and we don't understand why."

One of the two papers relies on Hinode data that shows direct observations of this polar switch. The other paper makes use of a new technique observing microwave radiation from the sun's polar atmosphere to infer the magnetic activity on the surface. 

The asymmetry described in the papers belies models of the sun that assume that the sun's north and south polarities switch at the same time. In addition, both papers agree that the switch is imminent at the north pole, well in advance of general predictions that solar maximum for this cycle will occur in 2013. Lastly, the direct Hinode results also suggest a need to re-examine certain other solar models as well.

Measuring the magnetic activity near the poles isn't easy because all of our solar telescopes view the sun approximately at its equator, offering only an oblique view of the poles, when they require a top-down view for accurate magnetic measurements. Hinode can observe this activity annually with its high resolution Solar Optical Telescope that can map magnetic fields when observing them from near the equator. 

The microwave radiation technique described in the second paper makes use of the discovery in 2003 that as the sun moves toward solar maximum, giant eruptions on the sun, called prominence eruptions – which during solar minimum, are concentrated at lower solar latitudes -- begin to travel toward higher latitudes near the poles. In addition, the polar brightness in the microwave wavelengths declines to very low values.

"These prominence eruptions are associated with increased solar activity such as coronal mass ejections or CMEs, so CMEs originating from higher latitudes also point to an oncoming solar maximum," says Nat Gopalswamy. Gopalswamy is a solar scientist at NASA's Goddard Space Flight Center, who is the first author on the microwave observations paper, which was accepted by The Astrophysical Journal on April 11, 2012. "When we start to see prominence eruptions above 60 degrees latitude on the sun, then we know that we are reaching solar maximum."

To look at the prominence eruptions toward the poles, Gopalswamy and his team used observations from Japan's Nobeyama Solar Radio Observatory telescopes and the joint ESA/NASA mission the Solar Heliospheric Observatory (SOHO). They watched the sun in the microwave wavelengths – which are used to observe the area of the sun's atmosphere just above the surface, known as the chromosphere. 

Gopalswamy created precise techniques to use such microwave radiation to measure the intensity of magnetic activity on the sun's surface at the poles. By mapping the brightness of the microwave radiation throughout the chromosphere, the scientists showed that the intensity at the north pole has already dropped to the threshold that was reached in the last solar maximum cycle, suggesting the onset of solar max there. This is backed by the fact that prominence eruptions are also occurring at high latitudes in the north. Eruption activity in the south half of the sun, however, is only just beginning to increase – the first CME occurred there in early March 2012.

The Hinode data also shows this discrepancy between the north and the south. The Hinode results are reported by a Japanese team, led by Daikou Shiota a solar scientist at RIKEN Institute of Physics and Chemical Research, and were recently submitted to The Astrophysical Journal for publication. Shiota and his team used Hinode to observe the magnetic map of the poles every month since September of 2008. 

Early maps showed large, strong concentrations of magnetic fields that are almost all magnetically negative in polarity. Recent maps, however, show a different picture. Not only are the patches of magnetism smaller and weaker, but now there is a great deal of positive polarity visible as well. What once pointed to a strongly negative north pole, is now a weakly magnetized, mixed pole that will become neutral – which occurs at solar maximum -- within the month according to the team's predictions.

"This is the first direct observation of this field reversal," says Cirtain. "And it is extremely important to understanding how the sun's magnetism generates the solar cycle."

Ted Tarbell is the principal investigator for Hinode's Solar Optical Telescope at Lockheed Martin in Palo Alto, Calif., and he points out that the direct measurements showed the progress of the pole reversal, and highlights the earlier portion of the cycle in 2008.

Typical models of the magnetic flip, suggest that as active regions rotate around the equator, their higher, trailing edge – which is almost always the opposite polarity from the pole in their hemisphere – drift upward, eventually dominating the status quo and turning positive to negative or negative to positive. The Hinode data show that this transition at the north began before such drifting had a chance to occur.

"This is one of the most interesting things in this Hinode paper to me," says Tarbell. "How did the polar reversal start so early, even though the onset of the solar cycle, that is, increased activity at lower latitudes, hadn't begun yet?"

Tarbell thinks these observations mean that this model, too, may need to be re-examined.Such adjustments to models are of course expected whenever new and better data is collected. Indeed, David Hathaway, who is a solar scientist at NASA's Marshall, and who is a co-author on the microwave observations paper with Gopalswamy, points out that the idea that asymmetries exist in the sun is not completely new. 

Other work has recently emphasized symptoms of this asymmetry, measuring, for example, more sunspots in the northern hemisphere than in the south at the moment. "But most of the well-developed models don't incorporate the asymmetry in them," Hathaway says. "More complicated models that incorporate asymmetries do exist, but they have other ways in which they fail to match observations."

Continued study on these differences, using the best observatories as well as new techniques for analysis will help expand and improve our understanding of the sun, its 11-year cycle, and the great eruptions that occur on its surface.

Scientists will also keep their eye on the current cycle – numbered Solar Cycle 24 – because a polar switch at the north that is sooner than was expected also implies this may be a fairly small cycle in terms of the number of sunspots and amount of solar activity.

Image below: In 2008 in the northern hemisphere of the sun (left) Hinode observed large patches of negative polarity, shown in orange. In 2011, the same area showed much smaller patches and a more even distribution of negative and positive (blue) regions. 

 

                           Hinodeandsoh

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Image Credit: JAXA/Hinode

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Comments

This is an interesting story about a phenomenon that I was unaware of. Since the earth's magnetic field protects us from radiation arriving from solar wind, do astronomers see an increase in cosmic rays originating from stellar sources when the sun's magnetic field is at a minimum? I never thought about this problem before.

The assumption seems to be that the "Sun" completes a reversal as a single entity at its own instigation.

What perhaps would be of a more universal significance would be results from a focus on electromagnetic energy sources or 'waves' and 'troughs' of flux influencing stars as they (and we and the greater heliosphere) travel through space. Such a body as our solar system travelling 220+km/s WITHIN the Galaxy and the whole Galaxy travelling 630+/- km/s across space produces powerful vortices. Crossing the 'con trails' of other stellar bodies will have effects which may not yet be fully understood. The vortex action of ripping back and rolling over of the sun's and the heliosphere's polarity may be shown to have greater significance to our planet and existence than is noted here.

Nevertheless always interesting reports here.
With Thanks. David.

Hey guys, I admit that I'm far from an expert in solar science, more of a layman in that department (I'm an enviro scientist specialising in contaminated lands) but I've been wondering, won't this huge imbalance in the sun's poles eventually cause it to do the big switcharoo, maybe quite suddenly? How long does the sun's magnetic polarity reversal take to happen anyway? If they happen every 11 years or so, they can't take that long.

The earth's magnetic poles have been somewhat eratic lately too. What if a reversal of the sun's magnetic poles coincided with a reversal of the earth's poles? These apparently happen every 300,000 years or so, but the last one was 780,000 years ago, when men were practically still apes. We're long overdue. Most research indicates that a reversal takes thousands of years, but there are a couple of studies out there that indicate that sometime it may happen faster.

Do you think a reversal of the earth's magnetic field could coincide with a reversal of the sun's magnetic field, in our lifetime? Any comments or (constructive please) criticism appreciated.

Harry reports latest from sydneyobservatorydotcom says north pole of sun primarily south. No change from south pole. He says the delay of 2 years from last year may be happening again. One pole change follows the other by a lag of 2 years. So we are going to have a sun with south orientation for 2 years---what was the weather like 2001? And wasn't 1989 a weather bear? Recall Jan 2012 north hemisphere of the sun collapsed with rapid diminishment of the n pole on E.
If Miles Mathis is correct and antimatter enters primarily the south pole then won't we be increasing our heavily imbalanced toward matter system?

Our magnetic polar switch is still waiting altho I am assured it will occur. Curiously, as far back as 4 cycles ago this delay in synch was noticed. Is it getting longer? Is there any connection to our sun and a low field magnetic star? Could a strong magnetic field inside our Sol be responsible for the reversals of the outside lighter magnetic field? These questions occur to me as I see that science has not definitely determined why the poles magnetically reverse and a controlling dense inner magnetic field is not beyond the realm of possibility.

we don't fully understand. The laws of physics dictate that the core and magma must move and react exactly the way it does. I personally think it's impossible. The core, magma,and all things associated,would have slow down.Now think about that. Then all these things must reverse reactions and movements.This is effusive. Also,the laws of physics dictate the influence of the sun and moon upon the earth.correct me if I'm wrong, it is totally totally impossible. The recent findings can be explained by a tenth grader as cyclical events.I'm going to end here because I could go on for hours. SORRY I CI feel it is impossible for the earth's poles to switch. here's why;if the core moves,and the magma moves causing an electromagnetic reaction manifested as poles and lines of magnetic flux and all things associated with electromagnetism,which AN'T HELP IT Y2K Y2K Thank you. Have a happy yew near,GOD bless

Everyone is focusing in on all the negative fact....say the suns Northern magnetic field is ahead of the southern well be that as it may be i have been reading numerous articles on this up comeing event and most of the articles state that ITS NOT A HUGE PROBLEM most scientists have actually forgotin about the problem so would everyone please calm down with this all your doing is scaring everyone to death

The comet ISON will also be approaches it's perigee at the same moment as the Sun switches it's magnetic field. I wonder if this will effect the comets orbit?
The earth also switches it's magnetic field though this event takes much longer.


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