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An interesting perspective of the transition from one solar cycle to another is given by exploring the days with no reported sunspots.
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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.
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Fig 2 shows the cumulative number of spotless days during the transition. At end 2009, the number is 773 and still climbing five years after the first spotless day.
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Fig 3 shows the distribution of spotless days during each cycle transition since 1848. The current total is 773 days at end of 2009. 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.
| Version | Date | Description |
| 1.01 | 5/09/2008 | Initial. |
| 1.02 | ||
| 1.03 |
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