Heres to a weak sunspot cycle

Physicists at the Indian Institute of Science believe solar activity is at a 100-year low

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Every few years,there comes along a heartening piece of research that will have us believe global warming is not our cross to bear. One such happy theory that did the rounds a few years ago attributed rising temperatures on Earth to sunspotscool,dark regions of high magnetic energy that occur periodically on the Sun and are accompanied by intense solar activityand came with the more suspect corollary that soon,a dip in solar activity will cause a mini ice age. As it turns out,even as parts of India prepare for higher temperatures,solar activity is at a 100-year low and,according to experts,it is very unlikely to induce a cold wave.

Since the mid-19th century,astronomers have known that sunspots,which often have a magnetic field 10,000 times that of the Earth,follow an 11-year cycle. As it waxes to its peak,a cycle may be marked by as many as a hundred sunspots,violent explosions known as solar flares,and mass ejections of plasma from the Suns atmosphere. As recently as in February,two years into the new solar cycle known as cycle 24 kicked off,a giant solar flarethe largest in four yearsand a mass ejection triggered fears of a solar storm that could cause damage to the tune of $2 trillion. A large solar flare can release energy a thousand billion times that of an atom bomb and such a major discharge,which also hurls accelerated particles into space,can disrupt the Earths ionosphere and its magnetic field,interfering with radio and satellite communications and causing power grids to trip. Each sunspot cycle varies in intensitya stronger cycle will have more such events, says Arnab Rai Choudhuri,a professor at the Department of Physics,Indian Institute of Science,and an authority on sunspots,who has developed a theoretical model that predicts the intensity of a sunspot cycle. And the present cycle,he says,will be the weakest in a long time.

In the last 50-60 years,sunspot cycles have been particularly strong,with the exception of the last cycle. While there is no consistent explanation for this yet,we have been able to predict the strength of a cycle with our theoretical model,and we believe the present one will be weaker by 35 per cent than the last one, says Choudhuri,who published the theoretical model in a paper in the journal Physical Review Letters in 2007. Predictions by the US National Aeronautics and Space Administration have reached similar conclusions. The predicted size would make this the smallest sunspot cycle in nearly 200 years, says a report on the NASA website.

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After Galileo discovered sunspots in the early 17th century,these dark patches mysteriously disappeared for about 85 years,a period known as the Maunder Minimum that was marked by cooler temperatures across Europe. Through the period,the Baltic Sea and the Thames froze regularly. Scientists do not know why there hasnt been another such break in solar activity since. The fact is,the Sun is still shrouded in mystery. For instance,we do not fully understand why the temperature of the corona is about one lakh degrees Celsius while that of the surface is 6,000 degrees. The temperature of a sunspot is 4,500 degrees,which is why it appears darker. However,it has been shown that when there are sunspots,the overall radiation from the Sun is slightly higher than without sunspots, Choudhuri says.

Part of the reason solar processes are not well-understood is that the Suns magnetic field is much more complicated than the Earths. The Earths magnetic field is constant like that of a bar magnet,and it only flips poles once in hundreds of thousands of years. But while the Earth has only one North Pole and one South Pole,the Sun is criss-crossed by several shifting magnetic fields and thus has several polarities. Most of these magnetic fields reverse polarity every 11 years,giving rise to sunspot cycles. (In fact,sunspots of opposite polarity are known to occur in pairs in a line parallel to the Suns equator.) This strong magnetic field,combined with the Suns differential rotationthe Sun takes 27 days to complete one rotation on its axis,and its different parts rotate at different angles,causing regions to shift relative to each otherand a highly conductive hot mix of plasma create what is called a dynamo effect,which is responsible for sunspots and much of the other solar features. Exactly how this happens,we dont know yet.