Identification of Hot Plasma Anomalies in Solar Wind Using Fe Ion Charge Distributions

Abstract

A presence of high Fe charge states in the ionic charge state distributions of the solar wind (SW) plasma, commonly characterized by the mean charge Q Fe , provides valuable information on heating processes in the SW sources. We study the relationship between the parameter Q Fe and the charge state distributions of Fe ions using the Solar TErrestrial RElations Observatory/PLAsma and SupraThermal Ion Composition data on the beginning of the 24th Cycle (2010 January–2011 July). We find that the Fe charge state distributions related to SW with Q Fe  ≈ 8–10 have an uni-modal shape peaked around Fe 8+ –Fe 9+ . When the Q Fe value increases, the distributions change: at first, the profile extends to higher charge states and then transforms into a bi-modal shape with a second maximum around Fe 16+ and a minimum around Fe 12+ . We discuss possible reasons for such bi-modality through the example of the interplanetary coronal mass ejection (ICME) event on 2011 February 24–26, where it was related to the heating of an eruptive prominence. For such an analysis, it is informative to have a special measure of the fraction of highly charged ions for the Fe ion charge distribution in SW. In addition to Q Fe , we introduce a parameter q 12 equal to a fraction of Fe ions with charges Q  ≥ 12 and show that this parameter can be applied for identifying both the large-scale hot plasma enhancements associated with ICMEs and small hot fragments of SW plasma, which may be associated with small-scale solar activity in various coronal structures.