By Frank Bosse and Fritz Vahrenholt
(Translated/edited by P Gosselin)
Our sun in May was normally active for the cycle. The mean sunspot number (SSN) was 52.1, which was 2/3 of the mean value for month number 90 into the cycle. The mean is calculated from the previously observed 23 solar cycles occurring since March 1755.
The sun quieted down immensely in June with a mean SSN of only 20.9. This means solar activity in June was only 27% of the mean solar activity observed for month no. 91 in all previous cycles. For the month it was a record, as never has month no. 91 of all the previous cycles been so low in activity. The old record low for month 91 was much more (SSN=39), occurring in Cycle No. 14, from 1902 to 1914.
In June 2016 a total of 9 days saw a single sunspot. This resulted in an impressive plunge in the chart:
Figure 1: Solar activity in the current Cycle No. 24 (red) compared to the mean of the previous 23 solar cycles (blue) and the similarly behaving Cycle 5 (black).
The following chart shows the deviation from the mean for the accumulated number of sunspots for each solar cycle, 91 months into each respective cycle:
Figure 2: Deviation from the mean value (shown by blue curve in Figure 1), for the accumulated number of sunspots up to month 91 for each cycle. Cycle 19 was the most active while Cycle 6 was the least active – 91 months into the cycle.
The current Cycle 24 is less active than Cycle 5 and 6 of the Dalton Minimum, which occurred from 1790 to 1830.
Figure 3: The smoothed mean value of the solar polar field (orange) and the difference amount between the poles (black) in Centi Gauss (cG).
Here we see that the mean value of the polar field is as high as the minimum of Cycle 23. Using the current reliable level of knowledge, this may be pointing that the coming Cycle 25 will be as strong as Cycle 24 in terms of sunspot activity.
However the difference in the polar field at 64 cG is at the highest level since recording began in May, 1976.
Looking closely at the black curve compared to the orange one in Figure 3, we note the following characteristic: Since the start of observation, never has the difference between polar solar field been above the mean for so long. Using a very precise time resolution (in the original data with 10-day intervals) we are able to see that the duration of this phenomenon in Cycle 24 so far is more than 3 times higher than anything registered in Cycles 21 – 23.
Could such a magnitude and long ongoing difference in the polar field have an impact on the future of solar activity? Could it be a sign showing that the “solar dynamo”, which is responsible for sunspot activity, has gone out of step? Time will tell.