Quasi-biennial Statistical Coupling of Solar Flares and Coronal Mass Ejections: Evidence for a Common Driving Process during Solar Maximum

Understanding whether solar flares and coronal mass ejections (CMEs) share a common physical driver or represent distinct eruptive phenomena remains a central challenge in solar physics. This study investigates the statistical coupling between the temporal occurrences of class ≥C1.0 flares and CMEs during the maximum phase of Solar Cycle 23 (1998−2003). To eliminate biases arising from their vastly different macroscopic occurrence rates, the analysis evaluates the local clustering dynamics of the events using the normalized interarrival stochastic variable h. A two-sample Kolmogorov–Smirnov test is subsequently applied to assess the statistical indistinguishability of the underlying temporal processes. While a static, global evaluation indicates completely decoupled statistics over the 6 yr period, a time-resolved analysis utilizing a sliding window uncovers a highly structured, quasi-biennial oscillation (∼2 yr) in the flare-CME similarity strength. Crucially, kinematic filtering reveals an energy-dependent phase inversion: epochs demonstrating robust statistical similarity between flares and the general CME population become strictly decoupled when only fast CMEs (≳900 km s−1) are considered, and vice versa. These findings indicate that the “common cause” hypothesis is not a permanent condition but a highly dynamic, conditional state. The quasi-biennial modulation of the statistical similarity is interpreted within the context of the double dynamo theory and the Gnevyshev Gap, suggesting that the deep-seated oscillatory modes of the solar magnetic cycle fundamentally dictate the varying topological complexity required to synchronize radiative outbursts and energetic plasma ejections.