By Frank Bosse and Prof. Fritz Vahrenholt
(Translated by P Gosselin)
Our sun was also very much less active in November than normal, comparing all solar cycles 1-23 up to month no. 120 since since the beginning of the systematic survey in 1755, the first year of solar cycle 1.The latest observed SSN (sunspot number) was a meager 5.9 for the monthly average.
On 16 days the sun was completely “spotless”. The maximum number over the days of November was 15, which does not mean that there were 15 spots – no, the number indicates that 5 spots were observed in a maximum of 1 spot group. So there was very low spot activity, only 20% of the average value.
Fig. 1: The current solar cycle 24 (red) compared to a mean cycle calculated as the average of cycles 1-23 (blue) and cycle 5 (black), which for years was quite similar and observed around 1800.
Fig.1 clearly shows that we had probably already arrived at the solar minimum at the beginning of 2018 (month 110 in the diagram). Will there be another “flare up” like in SC 5? The probability is rather low.
A comparison of all the observed solar cycles so far, 120 months into the cycle:
Fig. 2: The summed up monthly deviations between the observed SSN numbers and the respective mean value (blue in Fig.1) for all cycles up to the current cycle month 120 of SC 24.
The measurements of Cycle 24 are well recorded. It is very likely that we will stay in the minimum for another year with very little activity. This can also be seen in the solar polar fields, which stagnate at their maximum value. To illustrate this, we have graphically processed them as mean values from the solar northern and southern hemispheres. We always looked at the same time period, between the zero point (it is the respective spot maximum) and 2110 days afterwards, that is the last measuring point of the SC24 on November 27, 2018:
Fig. 3: The temporal development of the polar solar fields of the sun since 1980. The strength in the spot minimum, at the end of the respective graph when the fields become stationary and hardly change, is a good indicator for the activity of the subsequent cycle.
Figure 3 shows very clearly how hesitantly the increase in the current cycle occurred. The three predecessor cycles showed a much faster development after the zero crossing. Later, SC 24 then settled on a slightly higher value than SC 23. This could mean that SC 25 could become slightly stronger from 2020. But one should not expect too much accuracy from the method. It is clear that SC 25 will by far not become as strong as SC23 and 22, i.e. sub-normally active, see Fig. 2.
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