  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.
Different 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 different properties influence the HSS peak speeds
observed at Earth and draw from this to improve solar wind modeling. The
characteristics of the CHs of our sample were extracted based on the Collection
of Analysis Tools for Coronal Holes (CATCH) which employs an intensity
threshold technique applied to extreme-ultraviolet (EUV) filtergrams. We first
examined all the correlations between the geometric characteristics of the CHs
and the HSS peak speed and duration at Earth, for the entire sample. The CHs
were then categorized in different groups based on morphological criteria, such
as the aspect ratio, the orientation angle and the geometric complexity, a
parameter which is often neglected when the formation of the fast solar wind at
Earth is studied. Our results, confirmed also by the bootstrapping technique,
show that all three aforementioned morphological criteria play a major role in
determining the HSS peak speed at 1 AU. 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.
