Statistical Analysis of the Link between the Decrease in the Global Solar Magnetic Field in Cycle 24 and the Coronal Mass Ejection Parameters

摘要

During cycle 24, it is observed that both the polar and nonpolar magnetic fields of the Sun are becoming weaker relative to those in cycle 23; consequently, the interplanetary magnetic field (IMF) is decreasing. The mean values of the density, speed, and pressure of the solar-wind stream are also decreasing. A statistical study of the link of the IMF and the solar wind with the parameters of coronal mass ejections (CMEs) has shown that in cycle 24 the decrease in both the IMF and the solar-wind parameters are consistent with a decrease in the speed, angular width, mass, and energy of CMEs averaged over the Carrington rotation. The dependences of the CME parameters on the IMF magnitude are shifted toward lower magnitudes of the magnetic field and differ in cycles 23 and 24. The number of CMEs at the minimum of cycle 24 is significantly higher than that at the minimum of cycle 23, which may be a consequence of a decrease in the polar magnetic field at the minimum of cycle 24. A decrease in the average values of the parameters of CMEs with increasing their number suggests that in cycle 24 the number of weak CMEs is increasing. It is possible that a decrease in the average speed of CMEs and an increase in the number of CMEs with speeds below 700 km/s influenced a decrease in the average solar-wind speed in cycle 24.