Slow wind belt in the quiet solar corona

TL;DR

This study uses Solar Orbiter data to analyze the slow solar wind belt in the quiet corona, revealing its structure, acceleration, and magnetic field configurations during solar minimum.

Contribution

It provides new insights into the magnetic and plasma structures of the slow solar wind belt, linking observations with 3D MHD models and the S-web reconnection regions.

Findings

The slow wind accelerates from 150 to 190 km/s between 3.8 and 6.8 solar radii.

The slow wind is separated by high velocity shear regions from faster streams.

The S-web regions coincide with the slow wind latitudinal zones and are associated with open magnetic field lines.

Abstract

The slow solar wind belt in the quiet corona, observed with the Metis coronagraph on board Solar Orbiter on May 15, 2020, during the activity minimum of the cycle 24, in a field of view extending from 3.8 $R_\odot$ to 7.0 $R_\odot$, is formed by a slow and dense wind stream running along the coronal current sheet, accelerating in the radial direction and reaching at 6.8 $R_\odot$ a speed within 150 km s$^{-1}$ and 190 km s$^{-1}$, depending on the assumptions on the velocity distribution of the neutral hydrogen atoms in the coronal plasma. The slow stream is separated by thin regions of high velocity shear from faster streams, almost symmetric relative to the current sheet, with peak velocity within 175 km s$^{-1}$ and 230 km s$^{-1}$ at the same coronal level. The density-velocity structure of the slow wind zone is discussed in terms of the expansion factor of the open magnetic field lines that is known to be related to the speed of the quasi-steady solar wind, and in relation to the presence of a web of quasi separatrix layers, S-web, the potential sites of reconnection that release coronal plasma into the wind. The parameters characterizing the coronal magnetic field lines are derived from 3D MHD model calculations. The S-web is found to coincide with the latitudinal region where the slow wind is observed in the outer corona and is surrounded by thin layers of open field lines expanding in a non-monotonic way.