V. Oleneva

Abstract: The methods of nonparametric and multivariate statistics were used to study features of recurrent Forbush decreases (FDs) and to compare them with sporadic ones. The FEID database created and maintained in IZMIRAN allowed us to distinguish isolated FDs caused by high-speed streams from coronal holes (350 events) and by interplanetary disturbances from coronal mass ejections (207 events). Distributions of all parameters turned out to be more compact and to have smaller medians for recurrent events than for sporadic ones. Comparison of distributions of FD magnitude for different groups of events suggested that most FDs were related to coronal holes during the minimum between solar cycles 23 and 24. Multiple correlation coefficients between FD parameters and a set of solar wind parameters revealed that recurrent FDs depends less strongly on the characteristics of interplanetary disturbances than sporadic ones.