Abstract
Recently Pop (Solar Phys. 276, 351, 2012) identified a Laplace (or double exponential) distribution in the number of days with a given absolute value in the change over a day, in sunspot number, for days on which the sunspot number does change. We show this phenomenological rule has a physical origin attributable to sunspot formation, evolution, and decay, rather than being due to the changes in sunspot number caused by groups rotating onto and off the visible disc. We also demonstrate a simple method to simulate daily sunspot numbers over a solar cycle using the Pop (Solar Phys. 276, 351, 2012) result, together with a model for the cycle variation in the mean sunspot number. The procedure is applied to three recent solar cycles. We check that the simulated sunspot numbers reproduce the observed distribution of daily changes over those cycles.
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Notes
Sunspot data are compiled by the US National Geophysical Data Center (NGDC), and are available at http://www.ngdc.noaa.gov/stp/solar/ssndata.html . The NGDC data are used throughout in this paper.
Data are available at http://ngdc.noaa.gov/stp/solar/sunspotregionsdata.html .
As noted in Section 2, the adherence of the overall sunspot number to an exponential distribution is only very approximate (by comparison with the observed distribution of changes in daily sunspot number, which follows the Laplace distribution quite strictly).
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Acknowledgements
P. N. gratefully acknowledges a University of Sydney Postgraduate Scholarship.
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Noble, P.L., Wheatland, M.S. Origin and Use of the Laplace Distribution in Daily Sunspot Numbers. Sol Phys 282, 565–578 (2013). https://doi.org/10.1007/s11207-012-0155-x
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DOI: https://doi.org/10.1007/s11207-012-0155-x