Abstract
We study the transient modulation of galactic cosmic rays (GCRs) due to coronal mass ejections (CMEs) and their associated structures detected during most part of solar cycle 24. The interplanetary counterpart of CMEs (ICMEs), while propagating in the interplanetary space, may be associated with the shock/sheath region. An ICME may (or may not) be the so-called magnetic cloud. Using the method of superposed-epoch analysis, we analyze cosmic-ray neutron monitor data together with various plasma and magnetic field data during the passage of interplanetary structures with distinct plasma and magnetic field properties. From a detailed analysis of plasma and magnetic field variations during the passage of the shock/sheath/magnetic cloud/non-magnetic cloud ejecta, together with the cosmic-ray neutron monitor data, we conclude that the high magnetic field regions are particularly effective in modulating the GCRs when the field inside them is high and turbulent also. Our results agree with the hypothesis that the transient decreases/Forbush decreases in GCRs are mainly caused by turbulent high field regions due to the scattering of the GCR particles.