Solar cycle minimum

SILSO (Sunspot Index and Long-term Solar Observations) is the World Data Center for the production, preservation and dissemination of the international sunspot number. The latter is an important parameter to gauge solar activity, and it is being used in hundreds of science papers every year.

Just last week, it published on its website a newsitem announcing that solar cycle minimum, i.e. the minimum between cycles 24 and 25, most likely has taken place in December 2019. As this concerns a smoothed value, and it is only the very first point indicating a rise of the activity, the date of the minimum still needs a full confirmation over the coming months.

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. This can be seen in the graph underneath.

Further information on the solar cycle transition can be found at their website




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