Each solar cycle, during the period of maximum activity, the magnetic field at the solar poles disappears and gets replaced by a magnetic field of opposite polarity. 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 phenomena.
The plot underneath was produced by the Mount Wilson Observatory (MWO) and shows the evolution of the magnetic field over the solar surface since 1975 (red is negative polarity, blue positive). Polar reversals during previous cycles have been indicated with green ellipses.
This switch of the polar magnetic fields does not take place overnight. Indeed, it may take even several months before they are permanently established.
The old polar field is replaced by opposite polarity field from the magnetic remnants of active regions, being transported towards the poles by the Sun's magnetic conveyor belt, as tree leaves floating on a rippling creek.
This is a slow process as can be seen in this figure from the Marshall Space Flight Center (MSFC), annotated by green arrows indicating the movement from the active region belt towards the solar poles (yellow is positive polarity, blue negative).
Also, observers here on Earth have an oblique view on the Sun's poles. As the Sun's axis is tilted, they have a better view on the Sun's south pole during the spring months, and on the north pole during autumn. This changing view complicates measurements and delays firm determination of the timing of the reversal, as can be seen in the undulating evolution of the polar field strength (see figure from the Wilcox Solar Observatory (WSO) below).
The figures above readily show that there can be several months to over a year in difference between the timings of the reversal at the respective poles. For example, during the previous solar cycle, the north pole switched about a year prior to the south pole. So, for a few months around 2001, there were actually 2 "south" poles on the Sun!
For the current solar cycle 24 (SC24), the reversal on the Sun's north pole has been going on now for about 4-5 years, with positive and negative polarities alternating each other.
However we are now seeing magnetic poles defined as positive North and negative south.
SC24 would be a low activity solar cycle, as the maximum polar field strength was the lowest since they started measuring nearly 40 years ago. Each time, the polar field has been weaker, and each time, the next cycle was a bit weaker too.
Most Scientists predicted maximum during 2013 purely based on a peak then a drop in activity directly afterwards, however I did not fall for the prediction as my research suggested this has happened before (Twin peaks).
One thing to remember going forward is every time we see weaker magnetic fields the following cycle is weak too, this is why I conclude SC25 will be near to or slightly weaker than the previous Cycle.
If indeed this plays out then we should expect SC26 to be near to SC5-6 During the period of Dalton minima.
Thanks for dropping in.
David.
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