CME activities on spotless days during descending phase of solar cycles 23 and 24

TL;DR

This study analyzes the characteristics of coronal mass ejections during spotless days in the descending phases of solar cycles 23 and 24, revealing differences in CME properties and questioning the predictive power of sunspot numbers for solar eruptions.

Contribution

It provides a detailed statistical comparison of CME properties during spotless days across two solar cycles, highlighting limitations of sunspot numbers as predictors of CME activity.

Findings

CME on spotless days are slower, smaller, and less energetic.

Cycle 24 has wider and more massive CMEs during spotless days.

CME characteristics differ between cycles but are similar during spotless days.

Abstract

Spotless days (SLDs) as well as CMEs in the decay phase of the solar cycle are believed to be a good predictor of the forthcoming cycle. A sequential increase in SLDs is observed since cycle 21, and cycle 24 has the highest number of SLDs (since cycle 14), which offers a unique opportunity to probe the CME characteristics that occurred during SLDs (hereafter CME_SLD), in a statistical sense. Here, we investigate the CME_SLD during the descending phases of solar cycles 23 (2004-2008) and 24 (2015-2019). The fraction of CMEs that occurred on SLDs is found to be 14 and 11%, for cycles 23 and 24, respectively, compared to the total CMEs that occurred in the aforementioned durations. CME_SLD that occurred on the visible side of the solar disk are found to be slower, smaller in width, and carrying low Kinetic energy and mass compared to the entire population of CMEs. The distribution of annual evolution of speed, angular width and acceleration of the CMESLD with the CMEs that occurred on the non-SLD days (hereafter CME_Non-SLD) for the descending phases shows that the CME_SLD are different from the CME_non-SLD in terms of characteristics (such as speed, width and acceleration). A comparative analysis of CME_SLD kinematics of cycle 23 and 24 shows that the weakest cycle 24 has wider and more massive events. In contrast, other parameters of CME_SLD such as speed, acceleration and Kinetic energy do not have a disparate nature. CME_SLD in both SC23 and SC24 are statistically similar. Therefore, this investigation suggests that SLDs, and hence the sunspot number, may not be a sufficient candidate to predict the solar eruptive activities (e.g. CMEs). On the other hand, our analysis of the relation between the strength of the geomagnetic storm and probable candidate parameters revealed Dst index to be very well correlated with the product of V and Bz.