Predicting amplitude of solar cycle 24 based on a new precursor method

Abstract

Abstract. It is shown that the monthly smoothed sunspot number (SSN) or its rate of decrease during the final years of a solar cycle is correlated with the amplitude of the succeeding cycle. Based on this relationship, the amplitude of solar cycle 24 is predicted to be 84.5±23.9, assuming that the monthly smoothed SSN reached its minimum in December 2008. It is further shown that the monthly SSN in the three-year period from 2006 through 2008 is well correlated with the monthly average of the intensity of the interplanetary magnetic field (IMF). This correlation indicates that the SSN in the final years of a solar cycle is a good proxy for the IMF, which is understood to reflect the magnetic field in the corona of the sun, and the IMF is expected to be smallest at the solar minimum. We believe that this finding illuminates a physical meaning underlying the well-known precursor method for forecasting the amplitude of the next solar cycle using the aa index at the solar minimum or its average value in the decaying phase of the solar cycle (e.g. Ohl, 1966), since it is known that the geomagnetic disturbance depends strongly on the intensity of the IMF. That is, the old empirical method is considered to be based on the fact that the intensity of the coronal magnetic field decreases in the late phase of a solar cycle in parallel with the SSN. It seems that the precursor method proposed by Schatten et al. (1978) and Svalgaard et al. (2005), which uses the intensity of the polar magnetic field of the sun several years before a solar minimum, is also based on the same physical phenomenon, but seen from a different angle.

Probability of occurrence of extreme magnetic storms

“…[15] Although the actual maximum sunspot number will be determined in a few years, we need to select the maximum sunspot number for solar cycle 24 from some predicted values to apply this statistical model. The maximum sunspot number of the solar cycle 24 was predicted to be as low as 75 by Svalgaard et al [2005], while based on a precursor method, it was predicted to be 84 [Yoshida and Yamagishi, 2010]. Although many other predictions are reviewed by Pesnell [2012], it is noteworthy that the prediction method by Yoshida and Yamagishi [2010] is one of the simplest, and it is consistent with many important observations of the weak polar field [Svalgaard et al, 2005] as well as the cycle length [Hathaway et al, 2002;Watari, 2008].…”

“…The maximum sunspot number of the solar cycle 24 was predicted to be as low as 75 by Svalgaard et al . [], while based on a precursor method, it was predicted to be 84 [ Yoshida and Yamagishi , ]. Although many other predictions are reviewed by Pesnell [], it is noteworthy that the prediction method by Yoshida and Yamagishi [] is one of the simplest, and it is consistent with many important observations of the weak polar field [ Svalgaard et al ., ] as well as the cycle length [ Hathaway et al ., ; Watari , ].…”

“…The maximum sunspot number of the solar cycle 24 was predicted to be as low as 75 by Svalgaard et al [2005], while based on a precursor method, it was predicted to be 84 [Yoshida and Yamagishi, 2010]. Although many other predictions are reviewed by Pesnell [2012], it is noteworthy that the prediction method by Yoshida and Yamagishi [2010] is one of the simplest, and it is consistent with many important observations of the weak polar field [Svalgaard et al, 2005] as well as the cycle length [Hathaway et al, 2002;Watari, 2008]. It is also consistent with the longer-term observation of cycle length as reconstructed from tree rings, i.e., a roughly 14 year cycle length was found in 14 C content of tree rings formed during the Maunder Minimum when the sunspots mostly disappeared, while a 9 year length was found during the Early Medieval Maximum Period (ninth to tenth century) when the solar activity was estimated to be persistently higher than average [Miyahara et al, 2004[Miyahara et al, , 2007[Miyahara et al, , 2008.…”

Difference between even- and odd-numbered cycles in the predictability of solar activity and prediction of the amplitude of cycle 25

“…In our previous paper (Yoshida and Yamagishi, 2010), we showed that the SSNs at points 1, 2, 3, 4, and 5 years before the minimum or the minimum SSN are correlated with the maximum SSN of the succeeding cycle, and that the SSN at a point 3 years before the minimum exhibits the strongest correlation. Yoshida and Sayre (2012), then, showed that a better correlation is obtained when the average SSN over a cycle is taken instead of the maximum SSN, and that the correlation coefficient becomes the largest when the average SSN is calculated by dividing cycles at a point 3 years before the minimum.…”

“…It was shown previously that the sunspot number (SSN) at a point 3 years before the minimum is well correlated with the maximum SSN of the succeeding cycle, and a better correlation is obtained when the maximum SSN is replaced by the average SSN over a cycle for which the average SSN is calculated by dividing cycles at a point 3 years before the minimum (Yoshida and Yamagishi, 2010;Yoshida and Sayre, 2012). Following these findings, we demonstrate in this paper that the correlation between the SSN 3 years before the minimum and the amplitude of the coming cycle differs significantly between even-numbered and oddnumbered cycles: the correlation is much better for evennumbered cycles.…”