Solar wind originating from the small coronal holes

Observations of the solar wind at the close to the Sun distances by the Parker Solar Probe (PSP) show most of the time very strongly variable solar wind plasma characteristics. Inspecting the PSP observations during first ten perihelion, together with this large variability, we have also found a significant number of intervals of enhanced solar wind velocity appearing simultaneously with the decrease of the solar wind density, which indicates that this solar wind is originating from the coronal holes. However, out of thirty such intervals only few of them show velocity above 500 km/s. Majority of the identified wind flows have velocity of only about 400 km/s indicating that this solar wind will not be clearly distinguished as a flow when observed at 1 au distances. Employing the magnetic connectivity tool (developed by ESA’s MADAWG group) to associate the solar wind observed by the PSP with their source regions on the Sun, we identified the sources of that enhanced solar wind observed by the PSP to be the small coronal holes.

In this study we present the characteristics of a solar wind flows originating from such small coronal holes at close to the Sun distances and compare them with the characteristics of the fast solar wind originating from the large coronal holes. We also discuss on the possible reasons why we do not find more intervals of the fast solar wind in the PSP observations and compare the characteristics of solar wind observed at close to the Sun distances and at 1 au.