Observations of high and low Fe charge states in individual solar wind streams with coronal-hole origin

TL;DR

This study analyzes individual coronal-hole solar wind streams, revealing that Fe charge states are highly variable and can resemble slow solar wind, with transitions mapped back to coronal structures, challenging previous assumptions about coronal-hole wind uniformity.

Contribution

It provides new insights into the variability of Fe charge states in coronal-hole solar wind and links these variations to specific coronal structures using combined modeling techniques.

Findings

Fe charge states in coronal-hole wind are often as high as in slow wind.

Transitions between high and low Fe charge states are mapped to specific coronal holes.

Variability in Fe charge states challenges the notion of uniformity in coronal-hole solar wind.

Abstract

The solar wind originating from coronal holes is comparatively well-understood and is characterized by lower densities and average charge states compared to the so-called slow solar wind. Except for wave perturbations, the average properties of the coronal-hole solar wind are passably constant. In this case study, we {ocus on observations of the Solar Wind Ion Composition Spectrometer (SWICS) on the Advanced Composition Explorer (ACE) of individual streams of coronal-hole solar wind that illustrate that although the O and C charge states are low in coronal-hole wind, the Fe charge distribution is more variable. In particular, \markmeold{we illustrate that the Fe charge states in coronal-hole solar wind are frequently as high as in slow solar wind. We selected individual coronal-hole solar wind} streams based on their collisional age as well as their respective O and C charge states and analyzed their Fe charge-state distributions. Additionally, with a combination of simple ballistic back-mapping and the potential field source surface model, transitions between streams with high and low Fe charge states were mapped back to the photosphere. The relative frequency of high and low Fe charge-state streams is compared for the years 2004 and 2006. We found several otherwise typical coronal-hole streams that include Fe charge states either as high as or lower than in slow solar wind. Eight such transitions in 2006 were mapped back to equatorial coronal holes that were either isolated or connected to the northern coronal-hole. Attempts to identify coronal structures associated with the transitions were so far inconclusive.