The distribution function of the average iron charge state at 1 AU: from a bimodal wind to ICME identification

TL;DR

This study analyzes the distribution of average iron charge states at 1 AU over 20 years, revealing a bimodal pattern linked to the solar cycle and proposing a new method for identifying ICMEs using charge state data.

Contribution

It introduces the bi-Gaussian distribution as a model for the charge state distribution and demonstrates its effectiveness in ICME identification and boundary determination.

Findings

$ angle Q_{Fe} angle$ shows a bimodal distribution related to the solar cycle.

$ angle Q_{Fe} angle > 12$ is a reliable proxy for ICME detection.

The distribution parameters evolve with the solar cycle.

Abstract

We aim to investigate the distribution function of $\langle Q_{Fe}\rangle$ at 1AU to check if it corresponds to a bimodal wind. We use data from SWICS instrument on board the ACE spacecraft along 20 years. We propose the bi-Gaussian function as the probability distribution function that fits the $\langle Q_{Fe}\rangle$ distribution. We study the evolution of the parameters of the bimodal distribution with the solar cycle. We compare the outliers of the sample with the existing catalogues of ICMEs and identify new ICMEs. The $\langle Q_{Fe}\rangle$ at 1 AU shows a bimodal distribution related to the solar cycle. Our results confirm that $\langle Q_{Fe}\rangle> 12 $ is a trustworthy proxy for ICME identification and a reliable signature in the ICME boundary definition.