An Estimate for the Size of Sunspot Cycle 24
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An Estimate for the Size of Sunspot Cycle 24 R.P. Kane
Received: 14 June 2012 / Accepted: 10 September 2012 / Published online: 23 October 2012 © Springer Science+Business Media Dordrecht 2012
Abstract For the sunspot cycles in the modern era (cycle 10 to the present), the ratio of RZ (max)/RZ (36th month) equals 1.26 ± 0.22, where RZ (max) is the maximum amplitude of the sunspot cycle using smoothed monthly mean sunspot number and RZ (36th month) is the smoothed monthly mean sunspot number 36 months after cycle minimum. For the current sunspot cycle 24, the 36th month following the cycle minimum occurred in November 2011, measuring 61.1. Hence, cycle 24 likely will have a maximum amplitude of about 77.0 ± 13.4 (the one-sigma prediction interval), a value well below the average RZ (max) for the modern era sunspot cycles (about 119.7 ± 39.5). Keywords Prediction · Sunspot cycle
1. Introduction Sunspots vary in number over an approximately 11-year cycle, where each cycle is determined on the basis of using 12-month moving averages of monthly mean sunspot number, the so-called smoothed monthly mean sunspot number. Conventionally, a sunspot cycle begins at the time of a minimum amplitude (RZ (min)) of the 12-month moving average value, rises to a maximum amplitude (RZ (max)) and ends at a subsequent minimum amplitude that marks the conventional start of the next sunspot cycle. Each sunspot cycle is numbered, with the present sunspot cycle being 24, and cycle 10 and onwards are here collectively called the modern era sunspot cycles. Prediction of the maximum amplitude and timing of a sunspot cycle is of vital importance, especially as related to the potential for damage to electronic components aboard earth-orbiting satellites (Dyer et al., 2003) and to the possible health hazards for astronauts (Lockwood and Hapgood, 2007). For the current sunspot cycle 24, a number of predictions previously have been made for its size, with the predictions spanning a large range of values from < 70 to > 170 (Kane, 2007a; Pesnell, 2008). Using aa(min) = 8.7 of geomagnetic aa index in conjunction with R.P. Kane () Instituto Nacional de Pesquisas Espacias, INPE C.P. 515, 12201-970 São Jose dos Campos, SP, Brazil e-mail: [email protected]
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R.P. Kane
the Ohl precursor method (Ohl, 1966, 1976), Kane (2010) previously predicted RZ (max) = 58.0 ± 25.0 for cycle 24, a value considerably below the mean for the modern era sunspot cycles (about 120). If this predicted value proves to be correct, then the predictions calling for cycle 24 to be a large maximum amplitude cycle (e.g., Dikpati, de Toma, and Gilman, 2006) will prove to be utterly erroneous. Other predictions of below average RZ (max) for cycle 24 include those of Clilverd et al. (2006) and Badalyan, Obridko, and Sykora (2001). In addition to the prediction by Kane (2010), Kane (2007b, 2007c, 2008a, 2008b) made several earlier predictions regarding RZ (max) for cycle 24. Kane (2007b) predicted cycle 24 to have RZ (max) = 130, based on solar activity at different solar latitudes;
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