By Frank Bosse and Fritz Vahrenholt
(Translated/edited by P Gosselin)
In November our sun was once again below normal in activity. The 84th month since the current solar cycle started in December 2008 saw a solar sunspot number (SSN) of 63.2, which was 72% of what is the mean for month 84 into a cycle since observations began in 1755.
Figure 1: Our current solar cycle (SC) 24 (red) compared to the mean cycle (blue) of the previous 23 cycles. The current cycle over the past year or so as been very similar to solar cycle number 5 (black) which occurred from 1798 to 1810.
What follows is a comparison of all cycles:
Figure 2: The accumulated monthly deviations anomaly from the mean value (blue curve in Figure 1) for each cycle.
The current solar cycle 24 is weak compared to the previous cycles beginning with solar cycle 18 (1945). The books are practically closed for the current cycle as it is not expected to become more active and activity is expected to trail off. We are experiencing the weakest solar cycle since the Dalton Minimum 1790-1830, which involved solar cycles 5, 6 and 7.
For estimating the solar sunspot activity of the next upcoming cycle, observing the polar fields during times of activity minima provides strong indications. We reported on this here. So what can we expect some three years before the awaited minimum?
Figure 3: The polar fields of the sun since 1976. (Source: stanford.edu)
Early indications of a modestly active solar cycle 25
Especially the south polar field (show in red in Figure 3) is beginning to show signs of strengthening a little, yet is still behind the values of the very active cycles that occurred during the second half of the 20th century. This could be an indication that solar cycle number 25 may not be much weaker than the current cycle, but also not stronger. We will know more in about 3 years.