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

Abstract

Context. The Sun is a highly dynamic environment that exhibits dynamic behavior on many different timescales. Variability is observed both in closed and in open field line regions in the solar corona. In particular, coronal holes exhibit temporal and spatial variability. Signatures of these coronal dynamics are inherited by the coronal hole wind streams that originate in these regions and can effect the Earth's magnetosphere. Both the cause of the observed variabilities and how these translate to fluctuations in the in situ observed solar wind is not yet fully understood. Aims. During solar activity minimum the structure of the magnetic field typically remains stable over several Carrington rotations (CRs). But how stable is the solar magnetic field? Here, we address this question by analyzing the evolution of a coronal hole structure and the corresponding coronal hole wind stream emitted from this source region over 12 consecutive CRs in 2006. Methods. To this end, we link in situ observations of Solar Wind Ion Composition Spectrometer (SWICS) onboard the Advanced Composition Explorer (ACE) with synoptic maps of Michelson Doppler imager (MDI) on the Solar and Heliospheric Observatory (SOHO) at the photospheric level through a combination of ballistic back-mapping and a potential field source surface (PFSS) approach. Together, these track the evolution of the open field line region that is identified as the source region of a recurring coronal hole wind stream. Under the assumptions of the freeze-in scenario for charge states in the solar wind, we derive freeze-in temperatures and determine the order in which the different charge state ratios of ion pairs appear to freeze-in. We call the combination of freeze-in temperatures derived from in situ observed ion density ratios and freeze-in order a minimal electron temperature profile and investigate its variability. Results. The in situ properties and the PFSS model together probe the lateral magnetic field configuration, the minimal temperature profiles allow to constrain the radial structure. We find that the shape of the open field line region and to some extent also the solar wind properties are influenced by surrounding more dynamic closed loop regions. We show that the freeze-in order can change within a coronal hole wind stream on small timescales and illustrate a mechanism that can cause changes in the freeze-in order. The inferred minimal temperature profile is variable even within coronal hole wind and is in particular most variable in the outer corona.

Properties and Geoeffectiveness of Solar Wind High‐Speed Streams and Stream Interaction Regions During Solar Cycles 23 and 24

“…It is noteworthy that structures from which high‐speed solar wind flows may remain present at the same phase of the Bartels rotation for up to several years (see, e.g., the high‐velocity signatures near the longitude corresponding to day 10, recurring from early 2005 until late 2006, or those near the longitude corresponding to day 2, recurring from mid‐2006 until late 2008). This is consistent with findings by Heidrich‐Meisner et al () who studied the same coronal hole structure for 12 solar rotations in 2006. The resulting HSS reached the Earth 11 times, yet exhibiting variability in its signature observed by ACE at L1 as the spacecraft mapping drifted to different regions within the coronal hole.…”

Influence of solar wind parameters on unsupervised solar wind classification with k-means

“…We found in our analysis that the charge states of O and Fe do not contain the same information. With this knowledge we cannot directly infer predictions about other charge states, but our analysis and Heidrich-Meisner et al (2017) indicate strongly that the inclusion of further charge states might be useful.…”

“…The charge state composition remains unchanged after the solar wind leaves the hot corona (Geiss et al, 1995;Aellig et al, 1997) and are not affected by any (known) transport effect since the ion charge states are 'frozen in' in the plasma. Thus, the O charge state ratio (n O 7+ /n O 6+ ) and the mean Fe charge state (q Fe ) can be considered as direct tracers of the coronal history of a solar wind stream (Zurbuchen et al, 2002;Zhao et al, 2009;Heidrich-Meisner et al, 2017). Since both charge state data products are determined in different parts of the corona they contain different information about the solar wind.…”