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

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 highest number of SLDs (since cycle 14), regarding it as one of the weakest cycles, which offer a unique opportunity to probe the CME characteristics that occurred during SLDs (hereafter CME_SLD), in a statistical sense. Here, we investigate the CME_SLDs 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. An increase in the number of CME_SLDs is revealed after 2004. Further, CME_SLDs that occurred on the visible side of the solar disk are found to be slower, smaller in width, and carrying low K.E. and mass compared to the all population of CME. The distribution of  annual evolution of  speed, angular width and acceleration of the CME_SLD 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) which also exhibits solar cycle dependence. 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  K.E. do not have a disparate nature.   CME_SLD  in both the cycles 23 and 24 are similar in nature in a statistical sense. 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).