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

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.

7 pages, 6 figures

References in corpus (4)

• Small-scale magnetic islands in the solar wind and their role in particle acceleration. Part 1: Dynamics of magnetic islands near the heliospheric current sheet
• Forbush decreases and turbulence levels at CME fronts
• Understanding Forbush decrease drivers based on shock-only and CME-only models using global signature of February 14, 1978 event
• Relative contribution of the magnetic field barrier and solar wind speed in ICME-associated Forbush decreases

Cited by in corpus (3)

• Does Local Structure Within Shock-sheath and Magnetic Cloud Affect Cosmic Ray Decrease?
• Magnetic Cloud and Sheath in the Ground-Level Enhancement Event of 2000 July 14. II. Effects on the Forbush Decrease
• Pinching of ICME Flux Rope: Unprecedented Multipoint Observations of Internal Magnetic Reconnection during Gannon's Superstorm