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

Abstract

Context. 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. Aims. In this case study, we focus 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, we illustrate that the Fe charge states in coronal-hole solar wind are frequently as high as in slow solar wind. Methods. 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. Results. 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.

Cold prominence materials detected within magnetic clouds during 1998–2007

“…In steady state solar atmosphere conditions, charge states of Fe and O freeze-in within four solar radii (Hundhausen et al 1968a(Hundhausen et al , 1968bBame et al 1974;Buergi & Geiss1986). For these reasons, the ion charge states in ICMEs can still reflect their temperature history (Richardson & Cane 2004;Heidrich-Meisner et al 2016;Wang & Feng 2016). Therefore, the low ionic charge states may be a reliable signature to identify prominence materials in the interplanetary medium.…”

Evolution of an equatorial coronal hole structure and the released coronal hole wind stream: Carrington rotations 2039 to 2050

“…The analysis procedure applied to the raw ACE/SWICS data is described in detail in Berger (2008) and has been applied in, for example, Berger et al (2011) andHeidrich-Meisner et al (2016).…”

“…The same approach has been applied in Heidrich-Meisner et al (2016) and Peleikis et al (2016), Peleikis et al (2017). Firstly, a solar wind package is mapped back ballistically to the source surface at 2.5 R under the assumption that the solar wind speed is constant between the source surface and the observer.…”

Small interplanetary magnetic flux rope

“…Ion compositionsare freezing-in near the sun if ionization and recombination timescales are larger than solar wind ion expansion time[59][60]. Inthe equilibrium statefor solar atmospheric conditions, ion compositions are freezing-in within four solar radii[61][62].…”