Observable effects of Interplanetary Coronal Mass Ejections on ground level neutron monitor counting rates

TL;DR

This study analyzes how interplanetary coronal mass ejections, especially magnetic clouds, cause ground-level neutron monitor count decreases, revealing relationships with ICME speed, rigidity, and deceleration.

Contribution

It provides new insights into the effects of different ICME structures on neutron monitor decreases and highlights the role of ICME speed and deceleration in producing Forbush decreases.

Findings

Magnetic clouds cause deeper FDs than ejecta.

Faster and higher rigidity ICMEs produce larger FDs.

Deceleration of ICMEs correlates with FD depth.

Abstract

In this work, non-recurrent Forbush decreases (FDs) triggered by the passage of shock-driven interplanetary coronal mass ejections (ICMEs) have been analyzed. Fifty-nine ICMEs have been studied but only the 25% of them were associated to a FD. We find that shock-driving magnetic clouds (MCs) produce deeper FDs than shock-driving ejecta. This fact can be explained regarding to the observed growing trends between decreases in neutron monitor (NM) count rate and MC/ejecta speed and its associated rigidity. MCs are faster and have higher associated rigidities than ejecta. Also the deceleration of ICMEs seems to be a cause in producing FDs as can be inferred from the decreasing trend between NM count rate and deceleration. This probably implies that the interaction between the ICME traveling from the corona to the Earth and the solar wind can play an important role to produce deeper FDs. Finally, we conclude that ejecta without flux rope topology are the less effective in unchaining FDs.