SCIENTISTS around the world are keeping a close eye on the sun as it embarks upon the process of switching its magnetic poles. The sun’s magnetic field changes polarity once every 11 years as its inner “dynamo” reorganises itself.
Scientists started tracking these 11-year-cycles in 1976 and the initial processes of the fourth flip have already started. “The polar field in the north has reversed direction. The south has been less active, so the reversal is delayed,” says Todd Hoeksema, director of Stanford's Wilcox Solar Observatory, one of the few observatories around the world that monitor the sun’s polar magnetic fields. The south pole is likely to complete its reversal in the next few months. Hoeksema explains that it is hard to be precise because the south pole is tipped away from the earth by a few degrees and cannot be seen well.
The flipping of the sun’s magnetic fields is a result of complex processes. At extremely high temperatures within the sun, matter exists in the plasma state—as a mass of positively and negatively charged ions. The plasma exhibits a vigorous up and down motion due to convection within the sun. As the plasma is charged, the motion ends up producing large-scale magnetic fields and leads to the flip. The redistribution of magnetic fields within sunspots (magnetic regions on the sun which appear in groups of two with opposite polarities and last for several days) also plays a role in the flip.
The only way to know when the flip occurs is to observe the sun’s magnetic fields through instruments called magnetograms, says Dibyendu Nandi from the Indian Institute of Science Education and Research, Kolkata. Magnetograms are coupled to telescopes, allowing an accurate determination of the distribution of magnetic fields on the solar surface. Such magnetograms can be ground-based or space-based. For example, NASA and the European Space Agency have satellites with magnetograms. In India, Udaipur solar observatory has instruments that study the sun from an island in Udaipur lake, says Nandi.
During the flip, the likelihood of solar flares and solar storms is high and the space is most tumultuous. Solar storms impact the operations of satellites, sometimes knocking them off. They create geomagnetic disturbance and impact telecommunications and flights over polar routes. They also pose a threat to astronauts and space probes. Some researchers are of the view that they might also affect earth’s climate. “Reversal of the sun’s magnetic field will have consequences throughout the solar system since the domain of the sun's magnetic influence extends far beyond pluto,” says Hoeksema.
The flip gives us clues to the natural processes that go on within the sun’s surface hidden from our view. Based on the time of the flip, one can predict how far the sunspot cycle has progressed and based on the strength of the dipole field that is generated following the flip, one can also predict how strong the next sunspot cycle will be, says Nandi.
Though the flip of the polar field is an indicator that we are at solar maximum (the time when the likelihood of solar storms is the most), in the past some of the biggest storms have not occurred until after the solar maximum. So we must be on our guard, cautions Hoeksema.
