We study the sunspot activity in relation to spotless days (SLDs) during the descending phase of solar cycles 11–24 to predict the amplitude of sunspot cycle 25. For this purpose, in addition to SLD, we also consider the geomagnetic activity (aa index) during the descending phase of a given cycle. A very strong correlation of the SLD (0.68) and aa index (0.86) during the descending phase of a given cycle with the maximum amplitude of next solar cycle has been estimated. The empirical relationship led us to deduce the amplitude of cycle 25 to be 99.13± 14.97 and 104.23± 17.35 using SLD and aa index, respectively as predictors. Both the predictors provide comparable amplitude for solar cycle 25 and reveal that solar cycle 25 will be weaker than cycle 24. Further, we predict that the maximum of cycle 25 is likely to occur between February and March 2024. While the aa index has been utilized extensively in the past, this work establishes SLDs as another potential candidate for predicting the characteristics of the next cycle.

We have studied the width and speed of coronal mass ejections (CMEs) and geomagnetic disturbance storm time (Dst) Index during ascending phase of solar cycles 23 and 24. We have classified total CMEs according to angular width and speed for the ascending period 1996-2002 and 2008-2014. We have found that the width of 62% CMEs is narrow, and 3% are Halo for the solar cycle 23 and 73% CMEs are narrow, and 2% CMEs are Halo for the solar cycle 24. The speed distribution of 65% CMEs has speed ≤ 500 km/sec and 4% CMEs has speed > 1000 km/sec for solar cycle 23 and 84% CMEs has speed ≤ 500 km/sec and 1% CMEs has speed > 1000 km/sec in cycle 24. The relationship between width and speed is more pronounced for fast ejecta (>1000 km/sec.), while slower ejecta shows more astronomically immense scatter. We have reported that the correlation between Dst and CMEs for ascending phase of solar cycle 24 is less than as compare to ascending phase of solar cycle 23.

This study analyzed the correlative study between the peak intensity of the geomagnetic storm, interplanetary magnetic field (IMF) and the peak value of various plasma parameters during the solar cycle 24. This study has been performed using hourly values of the geomagnetic storm time (Dst) <-50 nT for the period 2008 to 2016. 173 events of disturbance storm time with solar wind velocity ≥ 350 km/s were selected for the entire period 2008 to 2016. The peak value of Dst index is well correlated with IMF, southward component of the interplanetary magnetic field (B z), as well as the electric field. The southward component of the IMF is the fundamental cause of geomagnetic disturbance, and the effect of velocity is greater than the density effect. It is reported that there exists a linear relationship between Dst with IMF, B z and plasma parameters: Electric field (E y), proton density, solar wind velocity, and flow pressure.

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