Fairies circle the solar north pole
posted: Aug 31, 2012

Early August, several multi-legged small filament pillars could be seen dancing around the solar north pole. SDO-imagery shows that the dark and dynamic strands started to develop on August 3 in the northeast, and about half a dozen could be seen for a few days (image 1; August 4). Then around August 7, they start interacting with each other and with magnetic elements inside and outside the area they encircle. Normally, the solar rotation would guide them across the solar limb and out of sight, but being so close to the solar pole, the filaments and their frantic interactions were large enough to be seen from behind the north limb. Finally, on August 11 the filaments erupted in a spectacular way (image 2), as if being tossed up by a blanket held by firemen. The magnificent dance was nicely captured in this movie from SDO/AIA171 and AIA304 imagery.



Solar scientists are very interested in the solar poles, not so much to learn about the latest in fairy dances, but to see if these poles have already switched their magnetic polarities. Indeed, as long as observations of the solar magnetic field have been available, it has been known that the sun flip-flops its polar magnetic field around the time of the solar cycle maximum. These reversals are a key feature of the solar dynamo: the physical process that generates the sun's magnetic field necessary for the creation of sunspots and other magnetic appearances. The changing of the polar magnetic fields does not take place overnight. Indeed, it may take even several months before they are permanently established. There can also be several months to over a year in difference between the timings of the reversal at the respective poles.
All this can be deduced from super-synoptic plots of the solar magnetic field like this one from the Mount Wilson Observatory, showing the migration of the magnetic fields over the solar surface (red is negative polarity, blue positive). Reversals of past solar cycles are indicated with green ellipses.


The filamentary strands visible early August seem to indicate there is still magnetic flux of opposite polarity very near to the north pole, implicating the reversal is not complete. However, the magnetic maps clearly indicate that the solar north pole is on the verge of permanently switching its magnetic polarity. The southern pole is lagging, perhaps by as much as a year. These reversals are yet another sign that solar cycle 24 is approaching its maximum.