The Distribution Function of the Average Iron Charge State at 1 AU: From a Bimodal Wind to ICME Identification

Abstract

We aim to investigate the distribution function of the iron charge state, at 1 AU to check if it corresponds to a bimodal wind. We use data from the Solar Wind Ion Composition Spectrometer (SWICS) instrument on board the Advanced Composition Explorer (ACE) along 20 years. We propose the bi-Gaussian function as the probability distribution function that fits the average iron charge state, «Q_Fe», 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 catalogs of interplanetary coronal mass ejections (ICMEs) and identify new ICMEs. The «Q_Fe» at 1 AU shows a bimodal distribution related to the solar cycle. Our results confirm that «Q_Fe»>12 is a trustworthy proxy for ICME identification and a reliable signature in the ICME boundary definition.