Predicting the Shape of Solar Cycle 25 Using a Similar-Cycle Method
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Predicting the Shape of Solar Cycle 25 Using a Similar-Cycle Method Zhanle Du1
Received: 13 March 2020 / Accepted: 4 September 2020 / Published online: 6 October 2020 © Springer Nature B.V. 2020
Abstract A similar-cycle method is applied in predicting the shape of Solar Cycle 25, through a more scientific definition to select similar cycles. Using the current solar minimum Rmin (25) as a reference, the six most similar cycles to Solar Cycle 25 are found to be Cycles 24, 15, 12, 14, 17, and 10 (in that order). The monthly values of sunspot-number series for the whole of Cycle 25 are predicted by weighted averaging the corresponding ones in the six similar cycles. As a result, Solar Cycle 25 is predicted to peak around October 2024 with an amplitude of about Rm = 137.8 ± 31.3 and to end around September 2030. As a by-product, there might be a secondary peak eight months earlier. The similar-cycle method considers only the solar cycles with similar parameters rather than all ones as for regression methods. It has an advantage that it does not depend so much on the accuracy of the observation. Keywords Solar activity, sunspots, solar cycle · Prediction
1. Introduction Solar-cycle prediction is becoming an increasingly important topic in both solar and spaceweather physics (Du, Li, and Wang, 2009; Du, 2020a). Spacecraft operators want to understand the strength and peak time of an ensuing solar cycle before or around its onset for planning future space missions. So far, numerous methods have been used to predict the maximum amplitude [Rm ] of a sunspot cycle (Du, 2011a), of which some can be used before and some others can be used after the solar minimum [Rmin ]. At the time about two years after the solar minimum, one can use simple functions to describe the shape of the solar cycle (Stewart and Panofsky, 1938; Nordemann and Trivedi, 1992; Hathaway, Wilson, and Reichmann, 1994; Volobuev, 2009; Du, 2011b; Hathaway, 2015). At the early rising phase of the solar cycle, one can employ the growth rate to predict
B Z. Du
[email protected]
1
Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China
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Z. Du
the following Rm (Thompson, 1988; Cameron and Schüssler, 2008; Du and Wang, 2012; Yoshida, 2014). At the time around the solar minimum, the geomagnetic (Brown and Williams, 1969; Ohl and Ohl, 1979; Thompson, 1993; Kane, 2007; Du, Li, and Wang, 2009; Du, 2011a) and solar-precursor methods (Schatten et al., 1978; Schatten, 2005; Svalgaard, Cliver, and Kamide, 2005; Pesnell, 2008; Pesnell and Schatten, 2018) are two important ones to predict Rm . Dynamo-based models (Babcock, 1961; Leighton, 1969) have been used to predict Rm only recently (Dikpati, de Toma, and Gilman, 2006; Choudhuri, Chatterjee, and Jiang, 2007; Labonville, Charbonneau, and Lemerle, 2019). Yoshida and Yamagishi (2010) pointed out that the decrease rate of the smoothed monthly mean sunspot number during the final three years of a solar cycle can be used as a precursor fo
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