Improvement of solar-cycle prediction: Plateau of solar axial dipole moment

Abstract

Aims. We report the small temporal variation of the axial dipole moment near the solar minimum and its application to the solar-cycle prediction by the surface flux transport (SFT) model. Methods. We measure the axial dipole moment using the photospheric synoptic magnetogram observed by the Wilcox Solar Observatory (WSO), the ESA/NASA Solar and Heliospheric Observatory Michelson Doppler Imager (MDI), and the NASA Solar Dynamics Observatory Helioseismic and Magnetic Imager (HMI). We also use the SFT model for the interpretation and prediction of the observed axial dipole moment. Results. We find that the observed axial dipole moment becomes approximately constant during the period of several years before each cycle minimum, which we call the axial dipole moment plateau. The cross-equatorial magnetic flux transport is found to be small during the period, although a significant number of sunspots are still emerging. The results indicate that the newly emerged magnetic flux does not contribute to the build up of the axial dipole moment near the end of each cycle. This is confirmed by showing that the time variation of the observed axial dipole moment agrees well with that predicted by the SFT model without introducing new emergence of magnetic flux. These results allow us to predict the axial dipole moment at the Cycle 24/25 minimum using the SFT model without introducing new flux emergence. The predicted axial dipole moment at the Cycle 24/25 minimum is 60-80 percent of Cycle 23/24 minimum, which suggests the amplitude of Cycle 25 is even weaker than the current Cycle 24. Conclusions. The plateau of the solar axial dipole moment is an important feature for the longer-term prediction of the solar cycle based on the SFT model.

Long-term solar activity studies using microwave imaging observations and prediction for cycle 25

“…This is true for both northern and southern hemispheres. The HL Tb is not sharply peaked at the sunspot minimum, somewhat similar to the flat axial dipole moment reported by Iijima et al (2017). In order to show the correlation between the HL and LL Tb, we performed a cross correlation analysis using the available LL and HL Tb data.…”

“…The analysis based on the polar microwave Tb thus predicts that the cycle 25 strength is not too different from that of cycle 24. We note that the prediction by Iijima et al (2017) for the 13-month smoothed total SSN is slightly below 80. This is similar to our smoothed cases if we average over the two hemispheres (77.6).…”

“…In the correlation plots reported by Schatten et al (1978) only two or three data points were used. Recently, Iijima et al (2017) used only 3 data points in the correlation of the axial dipole moment at the end of a solar cycle to the peak sunspot number in the next solar cycle. Figure 8.…”

Predictability of the Solar Cycle Over One Cycle

“…and Jiang & Cao (2018) applied the above scheme in a Monte-Carlo approach to predict the range of the polar field around the end of cycle 24 about 3-4 years before the minimum, including error bars. Similar approaches are also presented in Hathaway & Upton (2016) and Iijima et al (2017). In this paper, we generalize and update the previous method to investigate the predictability of the solar cycle over one cycle at different phases.…”

Effect of Magnetic Field Strength on Solar Differential Rotation and Meridional Circulation

“…Many researchers currently believe that the polar magnetic field at solar minimum is one of the best predictors of the next solar cycle (e.g., Svalgaard et al 2005). To estimate the polar magnetic field, the surface flux transport (SFT) model has often been used, and several studies have succeeded in estimating the polar magnetic fields (see Jiang et al 2014;Iijima et al 2017, and references therein). The SFT model requires several parameters such as the meridional circulation, the differential rotation, and the turbulent diffusion.…”