Interplanetary Coronal Mass Ejection Associated Forbush Decreases in Neutron Monitors

Abstract Interplanetary coronal mass ejections (ICMEs) are eruptions of plasma that propagate outward through the heliosphere. ICMEs, and the shocks they drive, cause a sudden decrease in the cosmic-ray flux in their local area of the heliosphere, called a Forbush decrease (FD). A method of defining FDs is established, and an automated process for identifying FDs in neutron monitor (NM) data is created. The correlation between ICME properties and FD magnitude in 12 different NMs is examined for 91 ICME-associated FD events occurring from 2001 through 2019 August. A number of ICME properties show positive correlation with FD magnitude, with decreasing correlation strength as NM cutoff rigidity increases.