Quantitative Analysis of the Influence of Solar CycleVariations on Timing, Number and Magnitude ofForbush Events at Moscow and Oulu Stations

Although investigations of short-term time-intensity changes, such asForbush decreases (FDs) and cosmic ray (CR) diurnal anisotropies, and long-term CR flux variations began decades ago, the influence of the 11-year solarcycle variations on FDs is rarely examined in detail. This study presents, forthe first time, the quantitative implications of the 11-year CR cycle on FDs.The rigorous analyses performed show that the 11-year Solar Cycle variationssignificantly influence the timing, number, and magnitude of FD event charac-teristics. Long-term variations can induce a significant number of spurious FDsin raw CR data. These false FDs can lead to serious false alarms in space weatherpredictions and FD-based research. Since these spurious FDs are ubiquitous, asevidenced by the results, manual or semi-automated case event analysis of FDsis inefficient. Thus, many existing catalogs of FDs created without accountingfor the 11-year Solar Cycle variation may be flawed. The efficiency and speedof the computer subroutines implemented in this work to account for both thelong- and short-term CR variations may be useful in predicting space weatherhazards.