Presence of Turbulent and Ordered Local Structure within ICME shock-sheath and its Contribution in Forbush decrease

TL;DR

This study investigates how turbulent and ordered magnetic structures within ICME shock-sheath regions influence cosmic ray flux decreases, revealing complex multi-step Forbush decreases linked to local magnetic substructures.

Contribution

It introduces a 3D-hodogram method to distinguish turbulent and ordered magnetic regions within ICME substructures, explaining multi-step Forbush decreases.

Findings

Turbulent and ordered IMF regions within shock-sheath affect cosmic ray variations.

Multi-step FD profiles are linked to local magnetic substructures.

3D-hodogram effectively differentiates magnetic field regions within ICME.

Abstract

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.