• DOI:10.1051/0004-6361/202142793
• Corpus ID: 247830452

Influence of coronal hole morphology on the solar wind speed at Earth

@article{Samara2022InfluenceOC,
  title={Influence of coronal hole morphology on the solar wind speed at Earth},
  author={Evangelia Samara and Jasmina Magdaleni{\'c} and L. Rodriguez and Stephan G. Heinemann and Manolis K. Georgoulis and Stefan J. Hofmeister and S. Poedts},
  journal={Astronomy \& Astrophysics},
  year={2022}
}

• E. Samara, J. Magdalenić, +4 authors S. Poedts
• Published 28 March 2022
• Physics
• Astronomy & Astrophysics

Context. It has long been known that the high-speed stream (HSS) peak velocity at Earth directly depends on the area of the coronal hole (CH) on the Sun. Di ff erent degrees of association between the two parameters have been shown by many authors. In this study, we revisit this association in greater detail for a sample of 45 nonpolar CHs during the minimum phase of solar cycle 24. The aim is to understand how CHs of di ff erent properties influence the HSS peak speeds observed at Earth and draw from this to improve solar wind modeling. Aims. The CHs were extracted based on the Collection of Analysis Tools for Coronal Holes which employs an intensity threshold technique applied to extreme-ultraviolet filtergrams. We first examined all the correlations between the geometric characteristics of the CHs and the HSS peak speed at Earth for the entire sample. The CHs were then categorized in two di ff erent groups based on morphological criteria, such as the aspect ratio and the orientation angle. We also defined the geometric complexity of the CHs, a parameter which is often neglected when the formation of the fast solar wind at Earth is studied. The quantification of complexity was done in two ways. First, we considered the ratio of the maximum inscribed rectangle over the convex hull area of the CH. The maximum inscribed rectangle provides an estimate of the area from which the maximum speed of the stream originates. The convex hull area is an estimate of how irregular the CH boundary is. The second way of quantifying the CH complexity was carried out by calculating the CH’s fractal dimension which characterizes the raggedness of the CH boundary and internal structure. Therefore, they need to be taken into consideration for empirical models that aim to forecast the fast solar wind at Earth based on the observed CH solar sources.