  The transient interplanetary disturbances evoke short time cosmic ray flux
decrease which is known as Forbush decrease. The traditional model and
understanding of Forbush decrease suggest that the substructure of
interplanetary counterpart of coronal mass ejection (ICME) independently
contributes in cosmic ray flux decrease. These substructures, shock-sheath and
magnetic cloud (MC) manifest as classical two-step Forbush decrease. The recent
work by Raghav et. al. (2016a) has shown multi-step decreases and recoveries
within shock-sheath. However, this can not be explained by ideal shock-sheath
barrier model. Further, they suggested that the local structures within the
ICME's sub-structure (MC and shock sheath) could explain this deviation of FD
profile from the classical FD. Therefore, present study attempts to investigate
the cause of multi-step cosmic ray flux decrease and their respective recovery
within shock-sheath in detail. 3D-hodogram method has been utilized to get more
details of the local structures within the shock-sheath. A 3D-hodogram method
unambiguously suggests the formation of small scale local structures within the
ICME (shock-sheath and even in MC). Moreover, the method could differentiate
the turbulent and ordered Interplanetary Magnetic Field (IMF) regions within
the substructures of ICME. The study explicitly suggests that the turbulent and
ordered IMF regions within shock-sheath do influence cosmic-ray variations
uniquely.

Space Physics