Spotless days around solar cycle transition - Dec 2012

An interesting perspective of the transition from one solar cycle to another is given by exploring the days with no reported sunspots.

This article covers the unusually long cycle 24/25 transition which on that measure accrued 819 spotless days over 2800 days.

Recent predictions (Solar Cycle Prediction (Updated 2012/12/10)) are that cycle 24 is likely to peak in six to nine months with a SSN of just 72, so it might not be very long before we see spotless days again.

Fig 1:

Fig 1 shows the percentages of the days in each month with no reported sunspots. The data is derived from the Provisional International Sunspot Number published by the Solar Influences Data Analysis Center (SIDC) . The use of parametric summary statistics like averages on the sunspot number is questionable since it is not a continuous scalar quantity. Reporting activity, or the lack of it, by reporting the percentages of days in a given period with no activity avoids the parametric statistics issue. The above chart uses a calendar month as the summary period, but the calculation of percentage of days in the month reduces the noise from month to month variation in length.

Fig 2:

Fig 2 shows the cumulative number of spotless days during the transition. During Sep 2011, it grew to 819.

Fig 3:

Fig 3 shows the distribution of spotless days during each cycle transition since 1848. The total at end 2012 was 819 days. Only 21% (3/14) of transitions in that period exceeded 736 spotless days, so this is certainly a slow transition.

My attention has been drawn to similar analyses which present the spotless days in a month by month, and number of contiguous spotless days by date.

Note: the graphs are updated regularly, you may need for force your browser to reload the freshest graphs.

Links

• Solar Influences Data Analysis Center (SIDC)
• NOAA daily solar data
• W1AW Propagation Bulletins
• http://solarscience.msfc.nasa.gov/papers/wilsorm/WilsonHathaway2006d.pdf
• http://users.telenet.be/j.janssens/Spotless/Spotless.html

Changes

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