标题： 太阳活动周期23和24下降期间无黑子日的CME活动 显示英文标题

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

摘要： 无云日（SLDs）以及太阳活动周期衰减阶段的日冕物质抛射（CMEs）被认为是对即将到来的周期的良好预测指标。自第21个周期以来，SLDs出现连续增加，第24个周期的SLDs数量最高（自第14个周期以来），这为从统计学角度研究在SLDs期间发生的CME特征（以下简称CME_SLD）提供了独特的机会。在这里，我们研究了太阳活动周期23（2004-2008）和24（2015-2019）下降阶段的CME_SLD。发现发生在SLDs上的CME比例分别为14%和11%，相对于上述时间段内发生的总CME数量。与整个CME群体相比，发生在太阳盘可见面的CME_SLD速度较慢，宽度较小，并且携带的动能和质量较低。对于下降阶段的CMESLD与发生在非SLD日的CME（以下简称CME_Non-SLD）的速度、角宽度和加速度的年度演变分布显示，CME_SLD在特性（如速度、宽度和加速度）方面与CME_non-SLD不同。对第23和第24周期CME_SLD运动学的比较分析表明，最弱的第24周期具有更宽和更重的事件。相反，CME_SLD的其他参数，如速度、加速度和动能则没有显著差异。SC23和SC24中的CME_SLD在统计上是相似的。因此，这项研究建议，SLDs，因此黑子数，可能不是预测太阳爆发活动（例如CMEs）的充分候选指标。另一方面，我们对地磁风暴强度与可能的候选参数之间关系的分析显示，Dst指数与V和Bz的乘积高度相关。 显示英文摘要

摘要： 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.