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Solar cycle minimum passed in December 2019

In January 2020, the 13-month smoothed sunspot number  rose for the first time since the maximum of cycle 24 (April 2014). Most probably, this indicates that the minimum between cycles 24 and 25 was passed in December 2019.

However, for now, this latest smoothed value in January 2020 is the very first point indicating a rise of the activity. So, the date of the minimum still needs a full confirmation over the coming months. For now, preliminary smoothed values, limited to less than 13 months, hint at increasing values over coming months. If the rising trend indeed continues, this date will become fully definitive.

Another indication of the transition between the two cycles can be drawn from counts of individual sunspot groups belonging to the old and new solar cycles. While most sunspot groups belonged to the last solar cycle until September 2019, the dominance switched to groups of the new cycle in November 2019.

So, this transition in terms of number of active regions falls in October 2019. This is close to December 2019. The slight time difference comes from three reasons:

  • The sunspot number also takes into account the total number of spots, and thus the size of the emerging active regions.
  • The time of the minimum depends on the respective trends of the declining phase of the past cycle and of the rising phase of the new cycles, over the 12 months surrounding the minimum.
  • The date of the minimum has a significant uncertainty range, as near the minimum, the activity hardly varies and is thus almost as low as the minimum level during a few months. The date of the minimum is thus always less sharply defined than the date of the maximum of the cycles, which are more sharply peaked.

Finally, since December 2019, solar cycle 25 produced a steady stream of small active regions, but the activity stagnated at a constant low level. However, since July and even more in the course of August 2020, the activity seems to truly take off, with at least one sunspot group visible on almost all days. Such a level of activity had not been reached since early 2019.

This late-breaking upward trend is now expected to accelerate over the coming months. So, be prepared for a more eruptive and interesting Sun!