Seasonal and Solar-Cycle-Phase Distributions of Solar Flares, Solar Proton Events, Intense Geomagnetic Storms, and Ground-Level Enhancements, 1996–2024

Background: Solar eruptions and their near-Earth consequences vary across the solar cycle, but the apparent distribution of disparate event classes requires comparable event definitions and observation windows. Objective: To describe seasonal and solar-cycle-phase frequencies of C-, M-, and X-class solar flares, solar proton events, intense geomagnetic storms, and ground-level enhancements during 1996–2024. Methods: Publicly catalogued observations were tabulated by event onset year and calendar-month season. Phase comparisons were divided by the number of years assigned to each phase, whereas seasonal comparisons used event shares and calendar-day exposures. Results: The catalogued totals were 33,636 C–X flares (29,704 C, 3,683 M, and 249 X), 187 solar proton events, 127 intense geomagnetic storms, and 22 ground-level enhancements. Autumn accounted for 27.3%, 29.9%, 43.3%, and 36.4% of these four event classes, respectively. For all four classes, the largest events-per-year frequency was observed in the years designated as solar maximum. No ground-level enhancement was assigned to the minimum-phase years. Conclusions: The descriptive patterns are compatible with solar-cycle modulation and, for geomagnetic disturbances, a possible equinoctial contribution. The distributions alone do not establish terrestrial-season causation of solar eruptions, nor do they quantify catalog completeness or cross-event causal relationships.