3 Predictions for the size of solar cycle 23

Figure 4: Predictions of the maximum sunspot number of solar cycle 23 in Group A

Figure 5: Predictions of the maximum sunspot number of solar cycle 23 in Group B

The starting time of solar cycle 23 is generally regarded as May 1996 although Harvey & White (1999) claim that the minimum between cycle 22 and cycle 23 occurred in September 1996. Since then, solar cycle 23 has progressed for more than 4 years. The Sun is now in a period of rather high activity, but at present we do not know whether the maximum solar activity has occurred or not. A number of predictions of the maximum solar activity have been suggested for the cycle 23. Here we have collected 48 predictions, among which 17 were obtained by using the precursor methods and the other 31 were classified into Group A.

Predictions of Group A can also be divided into two parts by taking the observed value of the solar cycle 22 as a critical dividing criterion. As a result, 16 cases with lower values were put into one part and the remaining 15 cases with larger values into the other. All predictions of the two parts are presented in Fig. 4, while those of Group B are given in Fig. 5. In Fig. 4, we may note an unexpectedly large gap between the two parts of Group A. The average $\overline{R_{\rm M}}$ of the first part is 107.9 with a large variance $\sigma$ of 27.9. The average $\overline{R_{\rm M}}$ of the second part is 202.1 with a rather small variance $\sigma$ of 14.9. Three lines representing average $\overline{R_{\rm m}}$ and the upper and lower bounds of $\overline{R_{\rm m}}\pm\sigma$ are presented in Fig. 4 where the horizontal solid lines refer to the first part with lower values and the horizontal dashed lines to the second part, respectively. As seen from Fig. 5, predictions of Group B surprisingly concentrate in a rather narrow interval with an average $\overline{R_{\rm M}}$ of 162.3 and a variance $\sigma$ of 11.2. Three lines representing average $\overline{R_{\rm m}}$ and the upper and lower bounds of $\overline{R_{\rm m}}\pm\sigma$ are also included in the figure.