By Frank Bosse and Fritz Vahrenholt
(Translated/edited by P Gosselin)
The sun was also very sub-normally active in February. Although we are in the middle of the minimum, the sunspot number of 0.8 for the 123rd month into the cycle is very low. On 26 days of the month no spots were visible, only on 2 days was there a little, symmetrically distributed over both solar hemispheres.The only exciting question currently: When will the minimum be finished and will solar cycle 25 begin? Although 6 spots of the new cycle were already visible in February with a significantly higher resolution, estimates are difficult.March again was dominated by some spots of the “old” SC24. The rule: “weaker cycles often last longer than stronger cycles” could hold.
The monthly resolved spot activity of the Sun over the solar cycle (SC) 24 at the beginning of December 2008 (red) compared to a mean cycle, calculated from the arithmetic mean of all previously systematically observed cycles 1-23 (blue) and the not dissimilar cycle 5 at the beginning of May 1798.
The long solar minimum since October 2017 (cycle month 107) can be seen very well, the mean SSN in this period was only 7.1. The comparison of the cycles among each other follows:
The strength of the sunspot activity of each cycle in comparison. The numbers in the diagram are obtained by adding up the monthly deviations between the observed values and the mean value (blue in Fig.1) up to the current 123rd cycle month.
Figure 2 shows that five cycles (No. 8, 15, 16, 18, 22) did not have a month 123 at all. Instead the following cycle started. In this respect, the picture is now somewhat distorted towards the end of the cycle.
A look at the solar polar fields shows that the minimum may have passed the peak, both smoothed hemispheric values decrease. The maximum strength of the smoothed average is currently 64, in the last minimum we saw 55, in the minimum before SC 23 the value was 104.
There is a lot that points to a SC25 that will be slightly stronger than SC24, but will remain below the zero line (standing in Fig.2 for an average cycle). Thus the sun therefore likely to remain on low flame for another 12 years. The operators of satellites and the ISS will be pleased, the upper atmosphere expands less with less solar activity and this saves orbital manoeuvres to maintain the height of the objects.